Modulation of PSII photodamage in the green alga Dunaliella salina.

MELIS, ANASTASIOS; BAROLI, IRENE

Photosynthesis: Mechanisms and Effects.

Kluwer Academic Publishers

Lugar: Dordrecht, The Netherlands; Año: 1998; p. 2257 - 2260

The process of oxygenic photosynthesis entails damage to a functional component in the D1 reaction center protein of photosystem II (PS II). This photo-oxidative damage irreversibly alters the photochemical reaction center chloorophyll (Chl), inhibits the PSII charge separation reaction and stops photosynthesis. Chloroplasts recover from such irreversible photodamage through a multistep enzymatic repair process which involves a selective degradation of the inactive D1 protein, and de novo biosynthesis and integration of a nascent D1 in the PSII holocomplex. Photodamage occurs at all light intensities and the repair mechanism operates continuously under ambient plant growth conditions, thus constituting an in vivo PSII damage and repair cycle. When the chloroplast repair process cannot keep up with the rate of photodamage, inactive PSII accumulate in the thylakoid membrane. In consequence, the light-saturated rate and the quantum yield of photosynthesis are diminished. This condition is known as photoinhibition of photosynthesis. This paper summarizes some of the biological and physical parameters that modulate the rate of photodamage under in vivo conditions.