MICHAEL BREYMANN
Creative Coder // Technical Artist
JURASSIC WORLDIndustrial Light & Magic // 2015
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NO PLATE. This jungle set design is a full 3D build using instanced objects. The ground was sculpted in 3ds Max, then populated with grass, foliage, and trees. Assets inside the aviary at the end of the shot were conformed to fit the composition of the dome breach.
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PHOTOGRAMMETRY CLIFFS. The foreground grass and foliage in this shot are procedurally generated and defer-loaded at rendertime for memory efficiency. The cliff is a photogrammetry reconstruction of photographs from an aerial shoot in Hawaii, with additional geometry sculpting and retopology in Z-Brush and Maya.
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CAMOUFLAGE.
For this jungle sequence, I developed a new pipeline tool to exchange instanced foliage assets between departments. All foliage set design and layout was approved with proxy renders from the Generalist team, then the plant transforms and species tags were exported for simulation and rendering by the Creature Dev team.
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THE ISLAND.
A straightforward, old-school mattepainting of Isla Nublar, using only Photoshop and Nuke.
TRANSFORMERS: AGE OF EXTINCTION Industrial Light & Magic // 2014
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KNIGHTSHIP LANDING BAY. I built the 3D model of the Knightship landing bay based on a concept art. To balance the warm and cool tones of the exterior and interior lighting, I separated light contributions to multiple render channels. Little attention was given to adjusting the intensities and color before rendering, which allowed for quick iterations and reworking of the composition in Nuke, as well as greater control over the interactive lighting.
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PREHISTORIC INVASION. The miningships that invade Earth in the opening shot of Transformers: Age of Extinction were highly detailed hero models that didn't fit into 3ds Max scene memory, so I wrote a tool that automatically created cached versions for delayed load whenever new animation takes were published from the Layout Department. Multiple sun positions were cheated in 3D to achieve the desired backlighting on each ship. The cloud layers catching sunlight over Earth were projected as displcement maps.
PACIFIC RIM Industrial Light & Magic // 2013
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LEATHERBACK TAKES A HIT. The Kaiju monster in this shot crashes into a dock crane and tears it from its base to be used as a weapon against Gipsy Danger. I was responsible for all the FX in this shot: water spray upon impact, rain, dust plume, crane sparks.
ILM's fluid solver, Plume, supplied the grid-based advection, and Renderman was used for rendering.
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GIPSY TUMBLE. This shot required all the typical destruction effects: particle simulations for sparks and rain, voxel grids for the dust impact, instanced geometry for debris, fluid simulations for the streaming water.
WORK IN PROGRESS. These are a few example OpenGL renders that show the simluation data for water splashes and dust plumes on Gipsy Danger.
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DOCK FIGHT. The Houdini FLIP solver was used for the streaming water effects as well as the structured splashes in these two shots.
The motion of the creatures, debris, and wind provided the dynamic forces acting on the water.
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UNSTOPPABLE. Sidewinder missiles only bruise monsters the size of skyscrapers.
The explosions and smoke clouds were created with ILM's Plume fluid solver.
The missile trails and tracers are particle simulations.
THE LONE RANGERIndustrial Light & Magic // 2013
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PUFF PUFF. The train smoke on this action sequence was accomplished with Houdini's fluid solver and velocity grids. Careful balancing of pumping heat into the grid from the smokestack while allowing for dissipation once the smoke hit the cooler air outside creates the curling eddies.
THE AVENGERSIndustrial Light & Magic // 2012
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MAYDAY. Loki takes out the Quinjet. After an initial explosive engine blow-out, I wanted the resulting smoke cloud to churn with the draft of the working engine on the opposite wing.
Loki's scepter energy beam was created procedurally using Python noise functions and the engine explosion was simulated with ILM's Plume fluid solver.
Deep compositing with the Quinjet geometry allowed for an accurate holdout within the 3D volume.
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HULK HURTING. The Chitauri charoit tracer fire seen throughout The Avengers was a tool I developed and packaged for show-wide distribution using rule-based Python scripts. An RGB mapping of temperature distribution from the hot tip through the cooler tail allowed compositors to control the glow and energy flares.
For these two shots specifically, I simulated and rendered all FX: tracer fire, explosions, dust, smoke.
COWBOYS AND ALIENSIndustrial Light & Magic // 2011
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HE'S NOT DEAD YET. The surprise lake breach of this alien required splashing water, streaming water, spraying water, and a dash of guts and gore. Smooth particle hydrodynamics (SPH) was used for the water structure, and meshed ballistic particles were used for the spray and goo.
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MORE GORE. Being slashed in the face with a lazer scalpal makes even aliens cry. This sequence of shots required gooey, sticky green blood to ooze from the gaping head wound. Getting the viscosity and adhesion values just right, combined with arterial pressure that looked realistic was the real challenge here.
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NO PARACHUTE. Quick camera cuts like the ones seen in this sequence are especially difficult for FX artists.
A simulation that might look great from one angle might look terrible from another, so multiple simulations need to be run with similar, yet subtly different characteristics. That was the case with these four action shots in particular, where the camera framing caught every conceivable angle of the speeder plunging from the sky.
THE CURIOUS CASE OF BENJAMIN BUTTONMatteworld Digital // 2008
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PARIS, 1950s. I designed and built this full-CG shot of Paris, starting from mid-century aerial reference. The hero buildings in the foreground were modeled based on photographs, but the background buildings and trees were procedurally generated to follow splines extracted from street maps. The texturing was accomplished using photo-based camera projections from multiple perspectives, with occlusions auto-filled at render time based on viewing angle. The tools I developed from the multiple techniques used in this shot were eventually released as a consumer software product,
ZODIACMatteworld Digital // 2007
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TRANSAMERICA PYRAMID, 1969. I designed and built this full-CG shot of San Francisco's North Beach neighborhood based on historical reference photography. The building reconstruction and period details are an accurate representation of what the neighborhood looked like just after the iconic Transamerica Pyrimid erected the first girder beams.
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SACRAMENTO CAPITOL. Notice the perfectly linear translation of the camera in this shot. It's a subtle yet intentional giveaway that this is a CG shot, not a live action plate. Craig Baron and I flew over Sacramento at dusk with still cameras to capture multiple angles of the capitol building, then reconstructed their positions in 3D space with photogrammetry software. The buildings were then built using image-based modeling and textured with camera projections of the photos.
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FOLLOW THE TAXI. This shot used every technique in the book. I led the team that worked on the photogrammetry build of the environment, and animated, lit, and rendered all CG elements. The shot was designed to feel natural at the beginning, as though it was captured from a helicopter, but then break believability as the taxi turns the corner and the camera tracks perfectly on its rotation axis. We even experimented with stop-motion car models, which are traveling opposite the taxi at the end of the shot.
MAD GODKaleidoscope // 2016
STEREO 360 RENDERS. The Mad God virtual reality experience was the first project my company, , produced with
and . I approached Tippett with the idea to create a VR experience based on Phil's stop-motion
universe, using binaural audio cues to lead the viewer's gaze.All creative direction, animation, photography, and compositing was done by Tippett Studio, and the final animated sequence was delivered to Kaleidoscope for delivery in VR. I chose Unity as the rendering engine, targeting the Oculus Rift and Samsung GearVR as delivery platforms. Custom shaders were written in C# and GLSL to re-project and composite multiple equirectangular layers on the GPU. You can find Mad God on Wevr's
JURASSIC WORLD: APATOSAURUS Industrial Light & Magic // 2015
MIXING LIVE ACTION AND CG. Felix and Paul Studios produced this short experience with ILM providing the CG elements. I was responsible for the FX that ties the dinosaur with the photography: the tree limb and leaves that become a snack for the Apatosaurus, as well as the foot impressions left on the ground.
THE LAST MOUNTAINKaleidoscope // 2014
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LOW POLY WORLDS. Starting with a team of 2 and ramping up to 17 during peak production, I led a team of animators, modelers, and texture artists that kicked off The Last Mountain as part of San Francisco's first
The project took 5 months to complete with artists and developers working remotely. This decentralized production model we developed established the foundation of
and guides its mission to empower independent artists.
STAR WARS 1313Industrial Light & Magic // 2013
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REALTIME FLUID SIMULATION. Though not technically a virtual reality project, Star Wars 1313 got me really excited about the future potential of realtime graphics, and was the genesis of my decision to move into the burgeoning virtual reality industry. I worked as an FX artist with Kim Libreri and the talented team of artists and developers at LucasArts on this cinematic piece, which was rendered in 22ms/frame&#8212the bleeding edge of rendering in 2013.
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REALTIME LIGHTING. I was the lighting technical director on this sequence, which demonstrates the realism the LucasArts developers achieved with advanced shader using Unreal Engine 3.
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MICHAEL BREYMANN was one of those kids who dismantled all of his toys in an attempt to better understand how they worked. Still doing that to this day with grown-up toys, Michael is passionate about creative technology and its relationship to storytelling as an artistic medium.For the last decade, he has worked as a technical director and graphics programmer in the visual effects industry. His production experience has resulted in the development of new software and tools designed to enhance the immediacy of interaction between artists and computers.In 2007, he formed
to commercialize a photogrammetry toolset, the Mattepainting Toolkit for Maya, which is now in use by freelancers and studios around the world. The features and design implementation were informed by Michael's work at
from .In 2009, Michael joined
as an FX technical director working on particle and fluid simulations. After a brief stint as a pipeline consultant to
in Rio de Janeiro in 2010, Michael returned to ILM where he continued his work as an FX TD and 3D Environment Artist until he left to form , a virtual reality content company, in 2015.As CTO of Kaleidoscope, Michael developed realtime graphics technologies and global distributed workflows for artists and developers. In January 2017, he left Kaleidoscope to pursue independent VR development full time.
SANDBOXA place for unfinished things.Light E f f e c t s on t h e G r o w t h a n d M o r p h o g e n e s i s o f P o t a t o
Amer J of Potato Res (-367353Light E f f e c t s on t h e G r o w t h a n d M o r p h o g e n e s i s o f P o t a t o (Solanum tuberosum) In Vitro: A R e v i e wJ a n e t E. A. S e a b r o o k Potato Research Centre, Agriculture and Agri-FoodCanada, P.O. Box 20280, Fredericton, New Brunswick, E3B 4Z7 CANADA Tel: (506) 452-4831;Email: seabrookj@em.agr.caABSTRACTGrowth, m o r p h o g e n e s i s , a n d t u b e r i z a t i o n o f p o t a t o t i s s u e s in vitro are affected by light. M e a s u r e m e n t s o f the v a r i o u s a s p e c t s o f light t h a t c o n t r o l d e v e l o p m e n t a n d growth o f p o t a t o are o u t l i n e d . Physical p a r a m e t e r s like light sources, delivery o f t h e light source, a n d t h e d e g r a d a t i o n of c u l t u r e m e d i a by light are discussed. I r r a d i a n c e , p h o t o a u t o t r o p h i c growth in vitro, s p e c t r a l wavelength, a n d p h o t o p e r i o d modify t h e r e s p o n s e s o f p o t a t o t i s s u e s i n culture. A c c l i m a t i z a t i o n o f t i s s u e cult u r e p l a n t l e t s , v e g e t a t i v e growth, a n d t h e p r o d u c t i o n , quality, a n d d o r n m a c y o f m i c r o t u b e r s a r e modified b y light. New light s o u r c e s such as l i g h t - e m i t t i n g diode ( L E D ) l a m p s a r e b e c o m i n g a v a i l a b l e for in vitro r e s e a r c h a n d for m i c r o p r o p a g a t i o n o f p o t a t o . P u l s e d o r c h o p p e r light has t h e p o t e n t i a l t o save e n e r g y costs. Light effects o n p o t a t o p r o t o p l a s t s , a n t h e r c u l t u r e , v i r u s e r a d i c a t i o n , a n d in vitro c o n s e r v a t i o n are discussed. P o t e n t i a l n e w r e s e a r c h a r e a s are the effect of t h e spect r a l q u a l i t y of light o n r e g e n e r a t i o n o f s h o o t s a n d somatic e m b r y o s in vitro, end-of-day red a n d far-red light t r e a t m e n t s , axillary s h o o t f o r m a t i o n i n c u l t u r e d p l a n t l e t s , a n d t h e u s e o f LEDs. T h e i n f l u e n c e o f m o n o c h r o m a t i c s p e c t r a l f i l t e r s o n growth a n d developm e n t o f p o t a t o e s i n t i s s u e c u l t u r e could p o t e n t i a l l y lead t o i m p r o v e m e n t s i n p r o d u c t i v i t y . The r e l a t i o n s h i p b e t w e e n daily q u a n t u m light i n t e g r a l a n d p h o t o p e r i o d a n d t h e i r effects o n growth a n d m o r p h o g e n e s i s o f the p o t a t o will provide some useful a r e a s o f research.RESUMENLos p r o c e s o s de c r e c i m i e n t o , morfog~nesis y t u b e r izaci6n de los t e j i d o s de p a p a in vitro s o n afectados p o r la luz. Mediciones de los varios a s p e c t o s de la luz que c o n t r o l a n el c r e c i m i e n t o y d e s a r r o l l o de la p a p a s o n delineadas. Parfimetros f[sicos t a l e s como la f u e n t e de luz, difusi6n y su efecto en la d e g r a d a c i 6 n del medio de cultivo s o n discutidos. La i r r a d i a c i 6 n , el c r e c i m i e n t o f o t o - a u t o t r 6 f i c o in vitro, la l o n g i t u d de o n d a e s p e c t r a l y el foto p e r i o d o modifican las r e s p u e s t a s de los t e j i d o s de la p a p a e n cultivo. La a c l i m a t a c i 6 n de las plAntulas de cultivo de tejidos, c r e c i m i e n t o v e g e t a t i v o y p r o d u c c i 6 n , calidad y d o r m a n c i a de los m i c r o t u b ~ r c u l o s s o n modificadas p o r la luz. Nuevas f u e n t e s de luz como a q u e l l a e m i t i d a por las 1Amparas de diodo (LED) estAn s i e n d o d i s p o n i b l e s p a r a la i n v e s t i g a c i 6 n in vitro y la microp r o p a g a c i 6 n de la papa. La luz i n t e r m i t e n t e t i e n e el p o t e n c i a l de a h o r r a r los costos de energ/a. Los efectos de la luz sobre los p r o t o p l a s t o s de papa, cultivo de a n t e r a s , e r r a d i c a c i 6 n de v i r u s y c o n s e r v a c i 6 n in vitro s o n discutidos. Nuevas ~reas p o t e n c i a l e s de investigaci6n son, el efecto de la calidad e s p e c t r a l de la luz sobre la r e g e n e r a c i 6 n de los b r o t e s y los e m b r i o n e s somfiticos in vitro, t r a t a m i e n t o s con luz r o j a del final del dia y del lado l e j a n o del e s p e c t r o i n f r a r r o j o , f o r m a c i 6 n a x i l a r de b r o t e s e n plAntulas c u l t i v a d a s in vitro y el uso de LEDs. La i n f l u e n c i a de los f i l t r o s e s p e c t r a l e s monocromfiticos s o b r e el c r e c i m i e n t o y d e s a r r o l l o de plfintulas de p a p a e n cultivo de t e j i d o s p o d r i a p o t e n c i a l -Accepted for publication 11 January 2005. ADDITIONAL KEY WORDS: irradiance, filters, morphogenesis, photoautotrophic, photoperiod, spectral quality,tuberABBREVIATIONS:CO2, B, DOE diff DLI,DQLI,daily quFR, LAA, LEDs, light- PAR,photosynthetica PPF, photos PPFD, photosynthetic R, UV, ultraviolet354AMERICAN JOURNAL O F POTATO RESEARCHVol. 82m e n t e conducir a u n m e j o r a m i e n t o e n la productividad. La r e l a c i 6 n e n t r e la c a n t i d a d diaria de luz i n t e g r a l y f o t o p e r i o d o y s u s e f e c t o s sobre el c r e c i m i e n t o y m o r f o g ~ n e sis de la p a p a proporcionarKu a l g u n a s ~weas d t i l e s de investigaci6n.1997), and only a portion of this light is visible to the human eye. Light requirements for photomorphogenesis are in the near-nltra violet (300-380 nm), blue (430-490 nm), red (640-700 urn), and far-red (700-760 nm) regions of the light spectrum, and for photosynthesis between 400 and 700 nm (Hart 1988). Many fluorescent lamps used to illuminate plant tissue cul-INTRODUCTIONPotato ( S o l a n u m tuberosum L.) is a crop that grows best in cool temperate climates with full sunlight, moderate daytime temperatures, and cool nights. Short days generally induce tubers in potatoes, although many modern cnltivars can initiate tuberization in the long days of north temperate regions (Hawkes 1992; Tam et al. 1992). Greenhouse-grown potatoes require artificial light to extend the day during the fall, winter, and spring seasons. In northern climates greenhouse-grown plants may need supplemental light throughout the day to produce a crop of minitubers. The common perception that i n vitro cultures are less sensitive to light than plants i n vivo is not the case (Aksenova et al. ; Seabrook 1987; Seabrook et al. 1993). Photoperiod, irradiance, and light spectral quality can be used to control the growth and morphogenesis of potato tissues and organs in vitro, thereby in some instances, avoiding the use of growth regulators, which could possibly cause off-types (Aksenova et al. ; Seabrook 1987; Seabrook et al. 1993; Seabrook and Douglass 1998; Wilson et al. 1993). Potato plantlets i n vitro can produce microtubers in response to inductive short photoperiods (Garner and Blake 1989; Pelacho and Mingo-Castel 1991; Seabrook et al. 1993). Irradiance levels influence the etiolation of potato plantlets i n vitro (Fujiwara and Kozai 1995) and light quality can alter the morphology of plantlets (Seabrook 1987; Seabrook and Douglass 1998; Wilson et al. 1993). Potato tissues in vitro are generally not autonomous for photosynthesis and frequently depend on a source of organic carbon such as sucrose (George 1986). Experimental regimes for autotrophic growth of potato i n vitro using high levels of irradiance and supplemental CO2 have been reported (Kozai et al. 1988; Pruski et al. 2002). However, facilities using high irradiance levels are costly to build and require considerable inputs of electrical energy to operate at optimal temperatures (18 to 20 C) for potato tissue cultures. Light is the electromagnetic radiation that causes photochemical reactions in plants (Fujiwara and Kozai 1995; Tantautures emit light deficient in the far-red wavelengths, thus care must be taken to provide the spectral balance suitable for growth of cultures (Seabrook 1987; v~rflson et al. 1993). Morphogenesis of potato tissue cultures can be manipulated by light regimes, and to improve efficiency of propagation (Kozai et al. 1988; Niu et al. 1997; Prnski et al. 2002; Seabrook 1987; Seabrook and Douglass 1998; Seabrook et al. 1993; Wilson et al. 1993). The terms &daylength& or &photoperiod& are often used to describe the alternating light and dark cycles within a 24-h period, but it is the length of the dark period that determines the photoperiodic response (Vince-Prue 1994). This review will outline the importance of precisely defining the light regimes for potato tissue cultures used in research and commercial production, outline alternative methods of controlling growth and morphogenesis of potato tissues i nvitro, and offer insights into possible productive areas offuture investigation.Light MeasurementsIrradiance, irradiant energy flux density (Wm-2), or incident light flux density (pmol'm-2s-1) (Fujiwara and Kozai 1995) are commonly called light intensity. Irradiance is measured in different ways: photometrically, radiometrically, and in quantum terms, each of these components relates to a different property of radiant energy (Hart 1988). Light meters usually have three different sensors that perceive these different properties of radiant energy. Photometric measurements (lumens = lux or foot candles), which measure brightness and not energy or photons, are used by lighting engineers and in the light meters in cameras (Hart 1988). Photosynthetically active radiation or solar radiation on a plane surface is the action spectrum used by plants for photosynthesis (ca. 350 to 730 um) (McCree 1972). Photosynthetic research uses photosynthetic photon flux densities (PPFD) or photosynthetic photon flux (PPF) to measure solar radiation in watts m -2 (Sager and McFarlane 1997). Current horticultural usage measures PPFD by using the pyranometer probe of a light meter. Radiometric or pyranometric measurements of light detect all forms of radiant energy including infra-red radi-2005SEABROOK: LIGHT AND POTATO I N VITRO355ation and are not suitable for morphogenetic research on plants where comparisons of the energy associated with different wavelengths of light are important (Hart 1988). The daily quantum light integral (DLQI) is the PPF incoming per unit ground area, expressed as the sum of the total light for a day (mol m -z&d 1 = MJm-2d-1) and has been useful in horticultural research and pot plant production (White and Warrington 1984). Young plants appear to be particularly sensitive to DLQI (White and Warrington 1984). The greenhouse industry has been able to avoid the use of growth regulators (Carvalho and HeuveIink 2001) by focussing on DLQI. Research on plant morphogenesis requires the use of quantum sensors that measure light in ~mol& m -2 s -1. Whimijan and Heins (1983) provided empirical conversions for photometric, radiometric, and quantum units as a guide for various commonly used light sources in the scientific literature. Lightunit conversions require information on lamp type (e.g., coolwhite, warm white, Gro-LtLx, etc.) used and the wavelength interval emitted from the light source (Both 1994; Thimijan and Heins 1983). Consequently, conversion from one unit of light measurement to another is fraught with difficulty and can only be estimated if the lamp type, age, and output are carefully defined. As this information is not available in the references cited herein, no attempt has been made to convert units for this review. Spectroradiometers measure radiation at specific wavelengths of light and in plant science are usually calibrated to measure at 10-nm intervals providing a graphical presentation with quantity on the vertical axis and nanometers on the horizontal axis.close to the light source, increased space efficiency with the use of stacked vessels, and increased plantlet leaf area (Kozai et al.1992). No reports using high-pressure sodium or metal halide lamps for potato in vitro have been located by the author of this review.New Lighting TechnologiesLighting systems that allow for reduced power demand through the use of hybrid solar and artificial lighting (HYSAL), and the use of specialized electric lighting systems are in development (Cuello 2002). Two experimental HYSAL syst one uses xenon-metal halide lamps and the second uses LEDs. In both experimental systems, light mirrors and fibre optics are used as the solar conection systems. Potato is one of the crops being considered for life support in space (Cuello 2002), and efficiencies in light delivery for in v/tro systems for potato will undoubtedly result from this research (Wheeler 2002; Wilson et al. 1993). Light-emitting diodes (LEDs) are small lamps that convert electrical energy into light as a form of luminescence. They can now be used as a radiation source for plants (Bula et al. 1991; Jao and Fang 2004a) and as light sources for growth chambers (Okamoto et al. 1996). Using LEDs increased invitro shoot length in response to increasing FR/PPFD ratiowhen the R/PPFD ratio was 0.1-0.5 (Miyashita et al., 1997). Early LEDs had the disadvantage of low emission efficiency (Green et al. 2001). Pulsed or intermittent light has been considered for illuminating plants (Jao and Fang 2004b; Sager and Giger 1980). A German company, Oellerich GmbH Berlin, recently developed an intermittent light technology called Chopper-Light-Technology, which provides considerable s a ~ g s in energy costs with no reduction in the productivity of shoot cultures of several woody species (Pinker 2002). Light cycles other than photoperiodic cycles have been tested on potato plantlets in vitro (Hayashi et al. 1994). The authors tested 16 h light/8 h dark, 4 h light/1 h dark, 1 h light/0.5 h dark and 0.25 h light/0.25 dark such that the ratio of light to dark period was 2:1 in all treatments. The amount of electricity consumed for illumination per 24-h period was the same for all treatments. Dry weight increase of the plantlets was greater in the shorter light cycle treatments. Light-emitting diodes at 180 Hz (5.5 ms) and 59% duty ratio and 16-h light period were recommended for optimal growth of potato plantlets (Jao and Fang 2004a). Natural light used to illuminate potato tissue cultures in India andLight SourcesControlled environment facilities for plant tissue culture use fluorescent lamps occasionally supplemented with incandescent lamps to provide additional red (R) portions of the spectrum. The growth and morphogenesis of potato plantletsin vitro can be radically altered by using different types oflamps with varying spectral qualities (Charles et al. 1992; Sarkar et al. 1996; Seabrook 1987; Wilson et al. 1993). Light spectral distribution of fluorescent lamps can vary considerably depending on age (Dooley 1991). Sidewards lighting using fluorescent lamps or diffusive optical fibres (DOF) for illuminating cultures produced similar potato plantlets of cv Benimaru (Kozai et al. 1992). Using DOF reduced cooling costs, increased PPFD when culture vessels were placed356AMERICAN JOURNAL OF POTATO RESEARCHVol. 82Cuba produced acceptable cultures and considerable savings of energy (Alix et al. 2001; Perez-Ponce et al. 2000). Norton et al. (1988) applied a light pipe in conjunction with metal halide or high pressure sodium lamps to illuminate several ornamental species in vit)~o and reported that shoot length was affected. Kozai et al. (1992) used a prototype diffusive DOF light sources in which only photosynthetically active radiation (PAR) is emitted to illuminate in vitro Benimaru potato plantlets. Plantlets had shorter stems and increased dry weight, leaf area, and net photosynthetic rate, all improved characteristics for micropropagated plants. New high-intensity lamps powered by microwaves have improved spectral composition for plant growth, but reportedly have yet to be used in controlled environment chambers (Krizek et al. 1993).MODIFYING GROWTH A N D D E V E L O P M E N T OF POTATO I N V I T R O WITH LIGHTSurprisingly few experiments have reported testing the effect of irradiance levels and spectral quality of light on morphogenesis of potato in v/tro (Bajaj and McAllan 1969; Sarkar et al. 1996; Seabrook 1987; Seabrook and Douglass 1998; Wilson et al. 1993). Many authors simply state the environmental conditions employed with no mention of the testing of any other levels. In view of the reported photomorphogenetic control of shoot regeneration in vitro in tomato (Lercari et al. 1999), and grape (Ch~e and Pool 1989), and control of axillary shoot growth of tomato in vivo (Tucker 1975), it is surprising that litfie work on the effects of light on shoot growth and regeneration in potato has been reported. Light strongly promotes geneDelivery o f the Light SourceReflective surfaces of light ~ e s as well as incident light on the culture shelf can be factors influencing growth of cultures. Most laboratories illuminate plant tissue cultures in a horizontal plane from above the cultures. However, significant differences in the fresh and dry weight, leaf area, and shoot length of potato cv Benimaru were reported when stacked ctflture vessels were illuminated using fluorescent lamps with a sideward lighting system (Hayashi et al. 1992; Kitaya et al. 1995; Kozai et al. 1991).transfer from Agrobacterium to plant cells of Arabidopsisthaliana and Phaseolus acutifolius in vitro (Zambre et al.2003). The formation of callus from stem internode explants of potato and cell suspensions required a reduction in irrradiance from 600-1,500 lux to 500-600 lux (Cassells and Long 1982). A higher irradiance reduced callus colony formation by 80%.IrradianceIrradiance, or photon flux density available to plant tissue cultures, is controlled by the light source, the distance of the cultures from the source, and the shape and type of material used to fabricate the culture vessel (Fujiwara and Kozai 1995). Shading of the cultures by closures can be a significant variable (Fujiwara and Kozal 1995), and the type of closure used should be carefully monitored. Shading of cultures in test tubes can be partly alleviated by the use of slanted test tube racks. Fluorescent lamps provide a reasonably even horizontal illumination if they are placed some distance (15-20 cm) from the cultures. A light meter should be used to test for uneven photon flux density across the shelf and the position of the lamps adjusted accordingly. Novgtk and Zadina (1987) used 10,000 lux to produce plants with &compact shoot growth and an expansion of the leaf blade area.& Struik and Wiersema (1999) cultured plantlets under 800 to 500 lux. Thus, it appears that increasing leaf area, perhaps through the use of high irradiance levels or various spectral qualities, should be investigated as a means of manipulating growth and mo~]ohogenesis. End-of-day light treat-Light a n d Media ConstituentsPhotochemical changes caused by light degraded (unchelated) iron (Fe) and caused the oxidation of EDTA in culture media (Albano and Miller 2001; Hangarter and Stasinopoulos 1991; Stasinopoulos and Hangarter 1990). Light degradation of growth regulator components of plant tissue culture media has been reported for indole acetic acid (Dunlap and Robacker 1988; Nissen and Sutter 1990; Posthnmus 1971; Yamakawa et al. 1979) and abscisic acid (Smith 1992). A combination of light and Murashige and Skoog (1962) salts at pH of 5 was partially alleviated by raising the pH of the media to 7.0 (Dunlap and Robacker 1988). Light can react with the antibiotic chloramphenicol to produce breakdown products deleterious to plant tissues in culture (Barg et al. 1983a, 1983b). Care should therefore be taken when storing plant tissue culture media, and when anomalous results are observed deterioration of media coltstituents should be considered.2005SEABROOK: LIGHT AND POTATO I N VITRO357ments with red and far-red light reduced transplant height and total leaf length of tomato plants grown in controlled environments (Decotean and Friend 1991). However, no similar work on potatoes has been located, and it would be interesting to determine ff red and far-red light applied to i n vitro plantlet cultures had a similar effect. High light intensity (120 pmol- m -2 /s -1) with a 12-b photoperiod was the most efficacious treatment for the rooting of in vitro-grown cuttings of potato (Wang and Hu 1985). Generally, in a medium lacking growth regulator, roots form readily on potato plantlets in vitro, and no other measures are necessary. The capacity of photosynthetic tissues of potato to tolerate high light irradiances (375 ~mol' m-2s-l) can be mediated by lowering the temperature at which in vivo plants are grown (Steffen and Palta 1989). Perhaps acclimatization of tissue cultured plantlets to conditions of high irradiance can be improved by lowering the temperature in vitro for similar time periods.tal CO2 to cultures grown in a medium with little or no sucrose to supply organic carbon (Pruski et al. 2002; Zobayed et al. 1999). Potato cultures in photoautotrophic conditions exhibited an increase in the number of nodes, dry weight, twice as many stomata, increased epicuticular wax, and thicker leaves compared to cultures grown with a lower PPE 20 g/L sucrose in the medium, and no supplemental CO2 (Zobayed et al. 1999). An inverse relationship between sucrose concentration and photosynthetic rate has been reported (Wolf et al. 1998). High net carbon assimilation rates cannot be sustained in potato plants grown with a nutrient film technique (Stutte et al. 1996). The nutrient film protocols used by Stutte et al. (1996) employed high CO2 levels, long (12 h) photoperiods, and high light irradiance. Stressed in vitro-grown potato plantlets exposed to high light and high C Q levels exhibited increased DNA methylation (Joyce and Cassells 2002). It is possible that increased DNA methylation is linked to the stress of high net carbon assimilation rates exhibited by in vitro-grown plantlets. The saturation irradiance for field-grown potatoes is 1,200 ~tE/m2/s (sic), which is ca. 60% of full sunlight (Dwelle 1985), and researchers culturing potatoes in vitro in photoautotrophic growth conditions could use this figure as a guide to the maximum irradiance necessary for potato under these conditions.Light Period and Vegetative GrowthA 16-h photoperiod is necessary to maintain vegetative growth of potato plantlets i n vitro (Dodds et al. 1992), although this is possibly an effect of a high DLI rather than photoperiod. Potato plantlet cultures are usually maintained in a 16-h photoperiod and an irradiance of 6,000 lux (Heszky and Nagy 1987). A 16-h photoperiod and an irradiance of ca. 1,000 lux (or 90 ~E m -z s -l) (sic)(lAndsay 1987); 2,000-3,000 lux (sic) (Tao et al. 1987) are generally recommended for the growth and morphogenesis of meristem tips (Lindsay 1987; Nov~ik and Zadina 1987; Wang and Hu 1985). Initiating material from etiolated tuber sprouts for plantlet cultures is common, and generally a 14~h photoperiod with an irradiance of 150 ~tE s-lm-2 (sic) is used (Chen and Li 1987; Lindsay 1987). Hussey and Stacey (1981) reported increased node formation in multiplication cultures with continuous light. However, as a potato extract was used in the medium, this might have influenced the results. Tissue-cultured potato plantlets grown in controlled environment chambers under 24-h illumination exhibit chlorosis and necrotic spotting (Cao and Tibbitts 1991; Cushman and Tibbitts 1996). In the author=s laboratory potato plantlets grown in vitro under continuous light do not thrive.Spectral QualitySpectral quality of light is the relative intensity and quantity of the different wavelengths emitted by a light source and perceived by photoreceptors within the plant. Cool-white or Grohix fluorescent lamps are commonly used for potato tissue culture (Lindsay 1987; Schilde-Rentschler and Schmiediche 1984; Tao et al. 1987). Lamps vary in spectral quality (Figure 1) (Anderson 1986; Pennazio and Redolfi 1973; Seabrook 1987; Wilson et al. 1993), and morphogenesis and growth can be affected (Seabrook 1987; Wilson et al. 1993). Increasing the red portion of the spectrum enlarged leaf area of tissue-cultured potato plantlets (Charles et al. 1992; Garner and Blake 1989; Seabrook 1987). Significant differences in number of leaves, leaf area, stem length, and (lit weight of potato cvs Shepody and Caribe grown under cool-white/Grolux lamp combinations were recorded by Seabrook (1987), Kadkade and Wetherbee (1983) and Marks and Simpson (1999). Axillary branching in potato plantlets in vitro in response to different light sources, e.g., Grolux fluorescent and cool-white + Grohix fluorescent (Seabrook 1987) is probably a response to R and FRPhotoautotrophic Growth In VitroPhotoautotrophic growth i n vitro is the application of very high (=150-375 p_mol-2s-1) light irradiance and supplemen-358AMERICAN JOURNAL OF POTATO RESEARCHVol. 82light (Heins and v~rflkins 1997; Tucker 1976). Fluorescent lamps with balanced spectral wavelengths accounting for the need for photosynthetic photon flux efficacy and R/FR photon flux ratio are needed for plant tissue culture (Murakami et al. 1992). Short pulses of red light applied to potato sprouts shortly after excision from the tuber promoted tuberization invitro, and treatment with far-red light delayed tuberization1998). Orchid plantlets cultured in a vessel made of 25-Fro Neoflon PFA film were larger and more vigorous than plantlets grown in test tubes (Tanaka et al. 1992). Seabrook and Douglass (1998) used yellow plexiglass filters, which removed blue light (380 to 525 nm) (Figure 2), to modify the growth of potato plantlets in tissue culture. Eliminating blue light portions of the spectrum increased plantlet height (Figure 3) and reduced the incidence of oedemas (intumescences), small pale yellow protuberances on leaves and stems which can affect large areas of the cultured plantlet (Seabrook and Douglass 1998). Specific wavelengths of light have therefore been implicated in the disruption of water relations within the plant tissues, leading to the formation of intumescences in vivo (Rangarajan and Tibbitts 1994) and in vitro (Seabrook and Douglass 1998).(Blanc et al. 1986), possibly indicating that the active form of phytochrome was present in the tubers. Management of plant growth in greenhouse crops using spectral filters has been reported (Decoteau et al. 1993; Mortensen and Stromme 1987), and only recently have spectral filters been used in vitro. Photo-selective films have been used to control the light spectrum and modify plant growth in greenhouses and controlled environments (Kuboda et al. 2000; Tsekleev et al. 1992; Tanaka et al. 1992; Van Haeringen et al.Plant Growth Regulators a n d LightIn VitroInteresting synergistic effects between IAA and R light onin vitro single-node cuttings of potato cv Miranda wereI0 2-~( ~1AGRO...... GROULXreported by Aksenova et al. (1994). In the presence of R light, IAA influenced stem length reduction and the induction of tuberization. Further, Aksenova et al. (1994) noted that kinetin in the presence of blue (B) light strongly promoted tuber for-l;f t01-~ I00.2-i~~ i /t &-~......CWF * AGRO CWF . GROULXSpectral Comparison Between Two Filters60.0o0.6E 0.2 .....50.0INCAN TL-84Filters40.0 E?c~==.... - ;&2,~o.1._m0E30.00.2-it,'f, iIi,*i,,,?,,,i,? \/%?:: :J&-,,&CWF * INCAN- .....cw~10.0Is°WAVELENGTH - - nm%;.....';;O4oo_AI I I = IflOOnm8001oooFIGURE 1. Spectral output ( n m ) of five common lamps used to illuminate potato cultures. AGRO = Agrolite fluorescent, GROLUX = Glolux fluorescent, CWF = cool-white fluorescent, INCAN = 60w incandescent lamp, TL-84 = Philips TL 40w/84RS fluorescent lamp. Differences in growth o f plantlets illuminated by various lamps were recorded (Seabrook 1987).WavelengthFIGURE 2. Comparison o f spectral wavelength o f light from cool-white fluorescent lamps filtered through clear and yellow plexiglass illters (Seabrook and Douglass 1998).2005SEABROOK: LIGHT AND POTATO I N VITRO359mation and increased total fresh weight as well as increasing the root + stolon: haulm ratio, apparently through the conjugation of IAA with glucose (Aksenova et al. 1990). Auxins and cytokinins apparently mediated the morphogenetic effects of light on potato in vitro (Sergeeva et al. t994). Red light has been implicated in the synth however, Sarkar et al. (1996) discerned differences in the chlorophyll content of two cvs (Kufri Jyoti and Kufri Chandramukhi) illuminated with fluorescent and incandescent lamps fitted with filters to provide white light enriched with R and B light. Sarkar et al. (1996) added gibbereUin to the culture medium, and this may have influenced the results. Red light is known to prevent leaf abscission in plants, but sub-optimal levels of R light have been implicated in dark-induced leaf abscission in mung bean (Decoteau and Craker 1984). Possibly, the use of R light could enhance the retention of leaves in tissue-cultured potato plantlets. Short pulses (5 rain) of R light have been implicated in shortening the time to tuberization forin vitro grown potato sprouts (Blanc et al. 1986), and R lightweight accumulation of potato plantlets in culture (Jao and Fang 2004b). Far-red light stimulated the conversion of 1-aminocyclopropane-l-carboxylic acid to ethylene in Begonia X hiemalis leaf and flower discs in vivo (Rudnicld et al. 1993). It would be interesting to test potato tissues for ethylene production when illuminated by various monochromatic light spectra, especially in view of the sensitivity of potato in vitro to restricted gaseous exchange (Jackson et al. 1991) and the formation of oedemas under certain light regimes (Rangarajan and Tibbitts 1994; Seabrook and Douglass 1998). The motivation for the Seabrook and Douglass (1998) study was the unacceptably short, rosette-type growth habits of certain potato cutivars such as AC Brador and Shepody so that multiplication rates were adversely affected. The use of a yellow plexiglass or cellophane filter increased stem length by 200°/5while maintaining the number of leaves and increasing leaf area. An additional benefit of removing blue light was the reduction in the incidence of oedemas (Seabrook and Douglass 1998). Aksenova et al. (1994) noted that B light in the presence of kinetin strongly stimulated potato tuber formation, increased fresh weight, and increased root + stolon to shoot ratio. Challakhyan et al. (1992), working with S. andigenum (sic) i n vivo, compared growth and morphogenesis under both B and R light andactivated the elongation of potato stems (Konstantinova et al. 1987). Concurrent blue and red light provided at the beginning of the photoperiod by LEDs resulted in an increase in fresh/dryYellow Filter Effects on Potato Plants~ntrOI w filterreported that ilhunination with blue light increased leaf area, &total mass (g),& and photosynthesis. Irradiation with UV light induced the biosynthesis of the stilbene phytoalexin trans-resveratrol in the leaves of both i nvitro and greenhouse-grown potato plants (Lippmann et al.10Ef.-2000). Trans-resveratrol (3,5,4'- trihydroxy stilbene) is reported to have anti-fimgal qualifies, and could be of use against fimgal pathogens of potato (Lippmann et al. 2000). It would be useful to know if trans-resveratrol could be used to partially protect potato from tissue culture plantlets from pathogens during acclimatization to the field. Blue light increased the number of axillary buds, and its influence depended on the fluence rate whereas R light influences were independent of fluence rate and reduced correlative inhibition (apical dominance) (Muleo et al. 2001). Light spectral quality could be used to manipulate both leafy shoot and plantlet production in potato rapid multiplication regimes.Brador Russet Burbank Shepodycm5Altering the spectral wavelength of lamps could change correlative inhibition (apical dominance) of the plantlet to produce more than one microtuber per whole plantlet.FIGURE 3. Effect of yellow filter on plantlet length o f three potato cultiv a r s g r o w n i n v i t r o . Leaf area from both treatments remained the same (Seabrook and Douglass 1998).360AMERICAN JOURNAL OF POTATO RESEARCH Microtubers exposed to light during induction and earlyVol. 82development tend to have well-developed periderm, are frequently green, and have improved disease and dessication resistance (Naik and Sarkar 1997). When microtubers were produced in light, more eyes were formed, survival was improved, and growth in the field of the subsequent plantlets was more vigorous (Gopal et al. 1998). Martlnez-Garcia at al. (2002) used S o l a n u m t u b e r o s u m ssp. a n d i g e n a , an obligate SD plant, to determine the interacting role of photoperiod and gibberellins in tuberization. They propose that tuberization in potato is similar to the flowering process in A r a b i d o p s i s : t w o separate pathways control tuber formation--a photoperiodicdependent and a gibberellin-dependent pathway. The induction of microtuberization i n v i t r o can be used to assess the maturity group (i.e., cultivar reaction to photoperiod) of potato germplasm (Lentini and Earle 1991; Pelacho et al. 1994; Veramendi et al. 2000). The spectral quality of light transmitted through various culture vessels can vary (Dooley 1991). Polycarbonate did not transmit light wavelengths less than 390 rim, glass &290 nm,and polystyrene &300 nm (Dooley 1991). Researchers shouldPhotoperiod Tuberization of potato can be promoted by environmental(photoperiod) and by developmental (growth regulators) factors (Martlnez-Garcia et al. 2002). This may explain the apparently contradictory information in the literature regarding the effect of photoperiod on tuberization i n v i t r o noted by Ewingand Struik (1992). Early studies on tuberization in v i t r o usedetiolated sprout sections from field-grown tubers in a culture medium containing high sucrose levels (Barker 1953; Lawrence and Barker 1963). Later reports studying photoperiodic effects on microtuberization also used etiolated sprout sections (Pelacho and Mingo-Castel 1991). Microtuberization of etiolated sprout sections is independent of light (Lawrenceand Barker 1963; Pelacho and Mingo-Castel 1991). The use ofsingle-node cuttings excised from tissue-cultured plantlets is more common and avoids the influence of the tuber tissue from which sprout sections originate (Hussey and Stacey 1981; Leclerc et at. 1994; Levy et aL 1993; Seabrook et al. 1993). Differences in the physiological state of stock material may account for some of the varying results reported. The photoperiodic reaction of the potato plant is wellknown (Chailakhyan et al. 1982; (Chailakhyan et al. 1992; Driver and Hawkes 1943; Ewing 1990; Mendoza and Haynes 1977). Photoperiod is a major morphogenetic control of tuberization in potato in tissue culture (Coleman and Coleman 2000; Seabrook et al. 1993). Potato plantlets i n v i t r o can be induced to produce microtubers by inductive short daylengths (Garnerand Blake 1989; Lentini and Earle 1991; Pelacho and Mingo-therefore be aware that some morphogenetically active wavelengths of light could be excluded from the illumination provided to cultures. The gaseous content in culture vessels containing potato plantlets was not affected by changing the light conditions (Buddendorf-Joosten and Woltering 1996).Castel 1991; Seabrook et al. 1993). Tuberization i n v i t r o can be induced in the absence of high sucrose levels, with no growth regulators and using inductive daylengths (Garner and Blake 1989). Ewing and Wareing (1978) reported that the amount andFIGURE 4. Examples of microtubers formed on in vitro single-node cuttings in r e s p o n s e to various photoperiodic treatments: ( a ) desirable microtub ( b ) microtuber ( c ) secondary
(d) secondary axillary microtubers. Leave were removed from the cuttings so that drawings could be prepared ( S e a b r o o k et al. 1993).type of tuberization on cuttings i n vivo was determined by the amount and type of tuberization stimulus, and Seabrook et al. (1993) demonstrated that the morphology (Figure 4) of tuber formation i n v i t r o was influenced by photoperiod. Time to tuberize (Veramendi et al. 2000), number of microtubers (Lentini and Earle 1991; Pelacho et al. 1994) and Adegree of tuberization@ (Veramendi et al. 2000) were used to categorize potato cultivars into maturity groups. Photoperiodic control of tuberization in potato tissues cultured i n vitro has been established (Dobrfinski 2000; Garnerand Blake 1989; Hussey and Stacey 1984; Lentini and Earleab2I1?mI1991; Martlnez-Garcfa et al. 2002; Seabrook et al. 1993). The use of media supplemented with gibberellins in the report by2005SEABROOK: LIGHT AND POTATO I N VITRO361Martinez-Garcia et al. (2002) may confound the results of experiments with regard to light requirements. Struik and Wiersema (1999) recommend incubation in the dark or at low light intensities (100-50 hix) with a light period of 8 h to induce microtubers. Lindsay (1987) reported incubating cultures to produce microtubers at a 16-h photoperiod and diffuse light (10 ~E m-2s-1). However, low irradiance levels can delay invitro tuberization (Jackson 1999). As a general nile, microtumWberization can be initiated by incubating cultures in darkness or by exposure to a 10. to 12-h photoperiod. The involvement of phytochrome in tuberization in vivo has been established (Batutis and Ewing 1982; Yanofsky et al. 2000). When environmental signals such as photoperiod are used to promote microtuberization (Blanc et al.1986; Jackson 1999) phytochrome may be involved. Blue light ( nm) promoted more tuberization than red light (600-700 nm) when applied for 16 h photoperiods (Aksenova et al. 1989).Microtuberization m0 100 8O0Exposure of potato plantlets from single-node cuttings to 8 h (SD) and 16 h (LD), and then subsequent single-node cuttings to SD and LD indicated that the production of microtubers was strongly influenced by genotype and photoperiod. Incomplete photoperiodic induction of microtubers resulted in secondary tubers, the production of stolons, and the formation of additional tubers in the axils of the leaf of single-node cuttings (Figure 4) (Seabrook et al. 1993). Potato cultivars (Jemseg, Kathadin, Russet Burbank, and Superior) varied in reaction to photoperiodic treatments with short days (8 h light) generally being the optimum treatment (Figure 5) (Seabrook et al. 1993). The effects of light on the greening of field-grown potato tubers are well known (Baerug 1962). However, Nalk and Sarkar (1997) reported that light-induced greening of microtubers can be used to improve the storage of microtubers, which otherwise tend to loose weight and shrink. A 16-h photoperiod at an h-radiance level of 30 ~tmol m-2s-1 for 10 days improved biomass loss during storage, and subsequent sprout emergence (Naik and Sarkar 1997). Light irradiance affects the duration of dormancy of potato microtubers (Tgtbori et al. 2000); the lower the irradiance, the longer the dormancy of cvs Desir6e and Gtilbaba. Microtubers induced and developed in an 8-h photoperiod compared with darkness exhibited shorter dormancy (Coleman and Coleman 2000; Gopal et al. 1998). Microtubers stored8O4o 200 100 80?)i ==-)+2O 1 2 3 4 LD-LD LD-$D SD-LD $D-$D Photoperiodic treatment miorotuber typem. mo +° DoF I G U R E 5. P e r c e n t a g e o f various t y p e s o f m i c r o t u b e r s ( s e e Figure 4) produced by p o t a t o single-node cuttings in vitro e x p o s e d to photoperiodic treatments. Plantlets e x p o s e d to LD = 16 SD = 8 h light. Single-node cuttings from p l a n t l e t s e x p o s e d to LD a n d SD and g r o w n in tuberization medium. Microtuber types: a = norr0~l; b = microtuber s u b t c -- s e c o
d = secondary axilhry m i c r o t u b e r ( S e a b r o o k e t al. 1993).362AMERICAN JOURNAL O F POTATO RESEARCHVol. 82under diffuse light had longer dormancy than microtubers maintained in the dark (Gopal et al. 2004).Pre-treatment o f P o t a t o Tissues In VitroAlthough light treatments can be used to improve the efficiency of in vitro propagation regimes (Economou and Read 1987), there are few reports on pre-treatment of potato tissue with light. Seabrook et al. (1993) reported that long day exposure of plantlets prior to tuber induction conditions and short days during tuberization increased yield and quality of microtubers in cvs Katahdin and Russet Burbank, but had little effect on cvs Jemseg and Superior. Pre-treatment of tissue culture plantlets in vitro with short photoperiods (8 or 12 h light) prior to planting them in greenhouses for the production of minitubers increased yield (Seabrook et al. 1993; Seabrook et al. 1995).Virus E r a d i c a t i o n f r o m Shoot TipsSubsequent to excision of the meristem including several leaf primordia, dark incubation is not advised (Huth and Bode 1970). Shoot explants excised from potato sprouts on tubers maintained in light (5.0 W m -2) grew better than those grown in darkness (Casseis and Long 1982). A photoperiod of 16 h rather than 8 h is recommended (Cassells and Long 1982; Mellor and Stace-Smith 1987; Nov~k and Zandina 1987). Although low light intensity (irradiance) (100 lux) is necessary to prevent browning of the tissues when incubating newly excised shoot tips, after 4 wk of incubation, light intensity can be increased considerably to 2 to 4 kilolux (Mellor and StaceSmith 1987; Wang and Hu 1985). Very high light intensities (30 kilolux) have been reported to be useful for incubating shoot tips (Klein and Livingston 1983). All recommendations of irradiance levels have to be noted with the caveat that both the light source (lamp) and the method of measurement have to be carefully noted to elicit any meaningful comparisons (Hart 1988). Pemmzio and Redolfi (1973) reported the effect of different light spectra on the growth and development of shoot tips of potato.A c c l i m a t i z a t i o n o f In Vitro Plantlets to E x Vitro ConditionsHigh light conditions (1,000 to 3,000 lux) have been recommended for preparing tissue culture plantlet for acclimation to soil (Murashige 1977). Kozai et al. (1988) tested three different irradiance (PPF) levels and determined that potato plantlets at the highest level (400 l~mol m-2s-1) were most vigorons and developed sufficient roots for acclimatization. Muraldshi and Harris (1987) also used high irradiance (4,000 lux) levels prior to planting out in the greenhouse. Although enriching the gaseous atmosphere of cultures may improve water-use efficiency and increase net carbon uptake, the possibility of poor root development due to the effects of elevated CO2 on photosynthesis over a long period of time must be considered (Chaves 1994). Thus, high irradiance levels and elevated CO2 may have the undesirable side effect of producing a plant unsuited to the stress of acclimatization. Steffen and Palm (1989) reported that one way to overcome this high irradiance stress exhibited by potato plants in vivo was to grow them at 12 C for 4 wk. The efficacy of low temperatures prior to acclimatization for alleviating high irradiance stress of invitro potato plantlets should be tested.In Vitro ConservationPotato germplasm is maintained at 1000 lux at a 16-h photoperiod at 6 C at the International Potato Centre (C.I.P.) in Lima, Peru (Dodds et al. 1991). However, Westcott et al. (1977) recommended a 16-h photoperiod, a light intensity of 4,000 lux at 22 C with monthly transfers to fresh medium for storage of potato germplasm, or the same conditions with storage at 6 C and less frequent transfers of tissues. Heszky and Nagy (1987) maintained single-node cuttings in vitro at 6,000 lux under a 16-h photoperiod. Light affected the viability of potato cultures maintained at low temperatures (Pruski et al. 2000). At the Canadian Potato Gene Repository at the Potato Research Centre, Fredericton, New Brunswick, plantlet cultures are maintained under a 16-h photoperiod with an irradiance of 80 ~unol'm-2s-~ combined with lower temperatures (12 C) for selected cultivars. It is surprising that light irradiance levels and spectral quality do not seem to have been investigated as a means of control of growth and development in germplasm conservation regimes.CONCLUSIONSNew technologies are required to provide high light irradiances for autonomous growth of potato cultures without the expense of cooling. Lighting systems such as hybrid solar and artificial lighting (HYSAL), light-emitting diodes (LEDs), pulsed light (Chopper light), and the use of natural light have the potential to conserve electrical power. Further research on2005SEABROOK: LIGHT AND POTATO I N V I T R O363t h e effects o f t h e interaction o f p h o t o p e r i o d with e x o g e n o u s a n d e n d o g e n o u s g r o w t h regulators o n microtuberization are n e e d e d to fully u n d e r s t a n d the tuberization p r o c e s s in potato. Studies o n the effects o f light o n d o r m a n c y o f m i c r o t u b e r s w o u l d b e useful for t h e s h i p m e n t a n d storage o f p o t a t o germplasm. Testing the daily light integral (DQLI) a n d phot o p e r i o d could d e t e r m i n e t h e physiological p a r a m e t e r s underlying the r e a c t i o n o f p o t a t o t i s s u e s to light i n vitro. The w e l l - k n o w n effect o f s e e d s o u r c e environment, climate, and soil c o n d i t i o n s o n the s u b s e q u e n t yield a n d g r o w t h o f the p o t a t o crop, leads to the c o n c l u s i o n t h a t the effect o f pre-treatm e n t with light (photoperiod, s p e c t r a l quality, a n d irradiance) o n various a s p e c t s o f p o t a t o tissue culture s h o u l d b e considered. Very little r e s e a r c h h a s b e e n r e p o r t e d o n the effects o f specific w a v e l e n g t h s and c o m b i n a t i o n s o f w a v e l e n g t h s o f light o n productivity o f rapid multiplication cultures, m i c r o t u b e r ization and r e g e n e r a t i o n (specifically s o m a t i c e m b r y o g e n e s i s ) o f p o t a t o in vitro. The relationship b e t w e e n t h e putative effects o f p h o t o p e riod a n d DQLI o n p o t a t o t i s s u e s i n vitro s h o u l d b e investigated particularly in view o f the r e p o r t e d effects o f light p e r i o d on vegetative growth.Bajaj YPS, and JW McAllen. 1969. Effect of varions light treatments on chlorophyll formation in excised potato roots. Physiol Plant 22:25-28. Burg R, N Umiel, and Y Nitzan. 1983a. Sensitivity of tobacco (Nicotiana tabacum) tissue culture to chloramphenicol and its photodegradation products. Plant Cell Envir 6:77-82. Barg R, N Umiel, and Y Nitzan. 1983b. Fate of chloramphenicol in tobacco (Nicotiana tabacum) tissue culture under various light regimes. Plant Cell Envir 6:83-88. Barker WG. 1953. A method for the in v/tro culturing of potato tubers. Science 118:384-385. Batutis EJ, and EE Ewing. 1982. Far-red reversal of red light effect during long night induction of potato (Solanum tuberosum L.). Plant Physio169:672-674. 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