ABSTRACT Photomorphogenic mutants of tomato were used to probe the possible involvement of phytochrome A in photosynthetic acclimation to shade. Plants of wild‐type Lycopersicon esculentum, the near isogenic mutants aurea (au, deficient in phytochrome A, and also possibly other phytochromes) and high pigment (hp, exhibiting exaggerated photomorphogenic responses), and the au/hp double mutant were grown in a greenhouse under either unfiltered daylight, or daylight attenuated by neutral density filters or green filters that simulated the spectral effects of vegetation shade. Growth and photosynthetic parameters were measured over a growing period of 15 d. Typical effects of simulated vegetation shade on extension growth were observed only in the wild‐type and hp strains; the presence of the au lesion resulted in reduced capacity to respond to vegetation shade by increased extension. Photosynthetic light saturation curves obtained using infrared gas analysis at 15 d indicated that neither the au nor the hp mutations caused serious reductions in maximum net photosynthetic rate in plants acclimated to full daylight, although the au/hp double mutant showed a significantly reduced maximum rate. In the wild‐type and hp strains grown under both neutral and simulated vegetation shade, the photosynthetic light saturation curves were similar. Plants with the au lesion showed a significantly lower capacity to acclimate to vegetation shade, as seen by their reduced maximum rate of net photosynthesis. However, in situ measurements of photosynthetic rate in the greenhouse were indistinguishable between the four strains. Thylakoid stoichiometry measurements revealed a very large increase in PSII/PSI ratio under simulated vegetation shade as compared with either unfiltered daylight or neutral density shade. These increases were not diminished in the phytochrome‐deficient au strains, and were even larger in the hp strains. The results indicate that the au lesion has little effect on the capacity of tomato to exhibit photoadaptation to simulated vegetational shade when measured at the thylakoid level. On the other hand, net leaf photosynthesis under vegetation shade can be significantly affected by the phytochrome deficiency caused by the au mutation, implying a possible role for one or more of the phytochromes in photoadaptation at the leaf level.
Plant Cell & Environment – Wiley
Published: Nov 1, 1993
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