Oxidative stress in Nostoc flagelliforme subjected to desiccation and effects of exogenous oxidants on its photsynthetic recovery

The metabolism of reactive oxygen species in Nostoc flagelliforme and effects of exogenous oxidants on its photosynthetic recovery were investigated to obtain insight into oxidative stress in desiccation and its possible damaging impact on photosynthetic apparatus. No ascorbate was detected with ascorbate oxidase in N. flagelliforme. Superoxide dismutase (SOD) remained active even after three years drying storage and its activity was 78% of that in fully recovered samples. The SOD activity decreased during desiccation or in drying storage. Intracellular active oxygen production was studied by incubating samples in BG(11) medium for 2 h and measuring the oxidation of 2',7'-dichlorohydrofluorescein diacetate. The production rate was 38.11 nmol DCF g (d.wt)-1 h-1 in dried field samples and was significantly higher than in fully recovered or air-dried samples. The balance between intracellular active oxygen production and the defense systems might break down in air-dried and dried field samples. Treatment with exogenous oxidants slowed the photosynthetic recovery especially with singlet oxygen. Oxidative stress might play an important role in desiccationinduced damages to the photosynthetic apparatus.