Photoinhibition and protection of photosystem I.

Over thirty years ago, when we first reported the selective photoinhibition of photosystem I (PSI) in chilling-sensitive plants at chilling temperatures, the inhibition tended to be regarded as a specific phenomenon observed only under peculiar conditions. We have since learned that PSI can be photoinhibited under many different conditions. The inhibition was observed with isolated thylakoid membranes under low light, or with some mutant plants under fluctuating light, or with plants illuminated by a series of saturating light pulses. Apparently, the sensitivity of PSI to photoinhibition is an intrinsic property of this photosystem. To understand the mechanism of PSI photoinhibition that are now shown to be universally observed in nature, a comparison of different types of PSI photoinhibition should certainly be useful. In this review, similarities and differences in the mechanisms of photoinhibition between different types of PSI photoinhibition, as well as the protection mechanisms from the inhibition, are discussed.