As sunlight is not always optimized for every terrestrial plant in terms of light quality, quantity and duration,
some plants suffer detrimental effects of sunlight exposure under certain conditions.
Photoinhibition of photosynthesis is a typical phenomenon representing harmful light effects, commonly observed in many photosynthetic organisms.
It is generally accepted that functional, structural loss of photosystem II complex(PS II) is the primary event of photoinhibition.
Accumulating data also suggest that singlet oxygen (1O2) is the main toxic species directly involved in it.
There are two different views on the specific site and mechanism of 1O2 production in the photosynthetic membrane.
One of them favors the PS II reaction center, where the primary charge pairs recombination occurs as a prerequisite for the generation of 1O2, and the other inclines to photosensitized 1O2 formation by a substance located outside PS II.
This article describes how we, as the advocators of the latter concept, have arrived at the conclusion that 1O2 immediately involved in PS II photodamage is largely generated from the Rieske center of the cytochrome b6/f complex and diffuses into PSII, attacking the reaction center subunits