Photosystem II damage and repair in Dunaliella salina. Acclimation to growth irradiances.

BAROLI, IRENE; MELIS, ANASTASIOS

Photosynthesis: from Light to Biosphere.

Kluwer Academic Publishers

Lugar: Dordrecht, The Netherlands; Año: 1995; p. 303 - 306

Illumination of plants with excess light leads to inactivation of photosystem II (PS II) in chloroplasts. The target of this photodamage is the reaction center protein D1. Chloroplasts recover from photodamage through selective degradation of damaged D1, followed by integration of a de novo synthesized D1 in the PS II complex. Under optimal growth conditions, this turnover also occurs, but the rate of photodamage does not exceed the rate of repair, and no adverse effect of irradiance on photosynthesis is observed. On the other hand, under either transient or steady state excess irradiance, the rate of photodamage might exceed the plant capacity for recovery, resulting in photoinhibition and the accumulation of damaged PS II centers in the chloroplast. We show that the rate of photodamage to PSII is a linear function of light intensity in the acclimated cells. At high irradiances, 160 kD protein complexes, which were suggested to represent inactivated PSII reaction centers, accumulate in the thylakoid membranes, implying that under conditions that accelerate damage to PS II, chloroplasts are not able to rapidly degrade and replace photoinactivated D1.