PARENT SESSION
Posters P1B Photo-oxidative stress, photoinhibition. Abstracts (394-443)

Photoprotection, photosynthesis and growth in Arabidopsis genotypes with differing levels of PsbS expression. Barry Logan^*,1, Samuel Terry¹, Krishna Niyogi², ¹ Biology Department, Brunswick, Maine, USA²

ABSTRACT- Energy dissipation protects the photosynthetic apparatus against the potentially damaging consequences of light absorption by safely converting excess light to heat. This process requires the presence of de-epoxidized carotenoids of the xanthophyll cycle (zeaxanthin or antheraxanthin), a low pH in the thylakoid lumen, and the minor light harvesting complex protein PsbS. We examined photoprotection, photosynthesis and growth in Arabidopsis genotypes whose capacities for energy dissipation have been altered via manipulation of PsbS expression (deletion or several-fold transgenic overexpression, which both lead to concomitant effects on energy dissipation). Plants raised in low (150 mol photons m^-2 s^-1) or high (1700 mol photons m^-2 s^-1) continuous light growth chambers exhibited expected acclimation of leaf pigment composition, photosynthetic capacity and major antioxidants to the light environment. However, no effects of altered PsbS expression were observed in either light environment. This contrasted with observations of greenhouse-grown plants, wherein midday Fv/Fm and growth (leaf number and rosette diameter) correlated with the level of PsbS expression. The greenhouse was managed such that plants experienced shady conditions for most of the photoperiod (<400 mol photons m^-2 s^-1), with the exception of approximately one hour during mid-morning when light intensities were highly variable and exceeded 1200 mol photons m^-2 s^-1 at times. Taken together, these data suggest that energy dissipation has its strongest protective effect in variable light environments.

KEY WORDS: Excess light, Xanthophyll cycle, Energy dissipation, PsbS