Arabidopsis Genotypes with Differing Levels of psbS Expression Differ in Photosystem II Quantum Yield, Xanthophyll Cycle Pool Size, and Aboveground Growth

Abstract

Thermal energy dissipation protects the photosynthetic apparatus against excess light and requires de‐epoxidized xanthophyll cycle carotenoids, a low thylakoid lumen pH, and PsbS, an integral membrane subunit of photosystem II. Here, we examine photoprotection, photosynthesis, and growth in Arabidopsis thaliana genotypes whose capacities for energy dissipation have been altered via deletion or transgenic overexpression of psbS. Plants were grown in a greenhouse, where they experienced low levels of incident radiation throughout most of the day, with an ∼40‐min midmorning period of exposure to high incident radiation each day. Midday ratio of variable to maximal fluorescence and photosystem II quantum yield increased slightly with increasing levels of psbS expression, while xanthophyll cycle pool size and conversion state were negatively associated with psbS expression. Notably, transgenic overexpression of psbS led to a 12% increase in rosette diameter, while mutants with no psbS expression exhibited 16% smaller rosette diameters and 18% fewer leaves than the wild type. Thus, the protective role of thermal energy dissipation manifested in plants grown in a light environment that included a period of high incident radiation, during which the various genotypes sustained differing levels of photosystem II photoinactivation, and periods of low incident radiation, when electron transport presumably limited the rate of photosynthesis and photosystem II photoinactivation influenced the overall rate of photosynthesis and hence growth.