DIFFERENTIAL LOCALIZATION OF ANTIOXIDANTS IN MAIZE LEAVES

The aim of this work was to determine the compartmentation of antioxid ants between the bundle-sheath and mesophyll cells of maize (Zea mays L.) leaves. Rapid fractionation of the mesophyll compartment was used to minimize modifications in the antioxidant status and composition du e to extraction procedures. The purity of the mesophyll isolates was a ssessed via the distribution of enzyme and metabolite markers. Ribulos e-1,5 bisphosphate and ribulose-1,5-bisphosphate carboxylase/oxygenase were used as bundle-sheath markers and phosphoenolpyruvate carboxylas e was used as the mesophyll marker enzyme. Glutathione reductase and d ehydroascorbate reductase were almost exclusively localized in the mes ophyll tissue, whereas ascorbate, ascorbate peroxidase, and superoxide dismutase were largely absent from the mesophyll fraction. Catalase, reduced glutathione, and monodehydroascorbate reductase were found to be approximately equally distributed between the two cell types. It is interesting that, whereas H2O2 levels were relatively high in maize l eaves, this oxidant was largely restricted to the mesophyll compartmen t. We conclude that the antioxidants in maize leaves are partitioned b etween the two cell types according to the availability of reducing po wer and NADPH and that oxidized glutathione and dehydroascorbate produ ced in the bundle-sheath tissues have to be transported to the mesophy ll for re-reduction to their reduced forms.