High-Irradiance Stress in Higher Plants and Interaction with other Stress Factors

Abstract

Exposure of leaves to light levels in excess of what can be utilized in photosynthesis often results in a decline in photosynthetic activity (1). This high-light effect is especially evident after return of the leaf to a low light level as a reduction in the photon yield of photosynthetic O₂ evolution or CO₂ uptake. In common usage the term photoinhibition includes any sustained reduction in photosynthetic activity induced by excessive light, irrespective of mechanistic considerations, but does not include transient reductions that are rapidly reversible and likely to reflect short-term regulation. In my talk today I will attempt to distinguish between two kinds of high-light-induced reduction in the efficiency of photochemistry of PSII: 1) an increase in the rate constant for dissipation of excitation energy in the antenna and 2) a decrease in the rate constant for the photochemistry of PSII which is likely to be caused by damage to the PSII reaction centers.