Superoxide and hydroxyl radical generation, and superoxide dismutase in PSII membrane fragments from wheat.

Illumination of photosystem II (PSII) membrane fragments of wheat (Triticum durum Desf. cv. Adamello) gave rise to both O2*- and *OH radicals adducts of the novel spin trap 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO). With time, OH became predominant displaying the conversion of O2- into OH. An intrinsic activity of superoxide dismutase (SOD) was found in PSII. Photoreduction of nitroblue tetrazolium (NBT) by PSII membrane fragments was induced by the addition of sodium azide and hydrogen peroxide. Western blotting of PSII proteins showed that a 29 kDa protein was recognised by an antibody against chloroplastic Fe-SOD from water lily. An increased formation rate of O2- was observed in damaged PSII where the SOD activity decreased following a treatment with a free radical-generating system. Damage in PSII consisted also in a decrease in chlorophyll and in carotenoids as well as in a change in the lipid : chlorophyll : protein ratio. Upon treatment a decrease in the unsaturation of PSII membrane fragments was also monitored together with a degradation towards more saturated molecular species of monogalactosyldiacylglycerol.