Effect of singlet oxygen generating substances on the ascorbic acid and glutathione content in pea leaves.

Ascorbate and glutathione levels were investigated in pea leaf discs exposed to various singlet oxygen generating compounds: eosin, rose bengal, monuron, acifluorfen and 5-amino-levulinic acid (ALA). The cellular level of the major antioxidant ascorbate was markedly decreased by the herbicides monuron, acifluorfen and ALA (in light-dependent reactions), as well as by the xanthene dyes eosin and rose bengal (independently of light). No significant accumulation of dehydroascorbate could be observed in any treatments. In contrast to ascorbate, the foliar glutathione levels were considerably increased by subtoxic or slightly toxic concentrations of eosin, rose bengal, acifluorfen and ALA in a light-dependent manner. Monuron treatments led to unchanged or decreasing glutathione contents. The activities of three antioxidative enzymes (ascorbate peroxidase, glutathione reductase and glutathione S-transferase) were also induced by eosin in light-dependent reactions.