CHANGES IN THE GLUTATHIONE LEVEL INDUCED BY TRANSPLASMA MEMBRANE ELECTRON-TRANSPORT IN MAIZE (ZEA-MAYS L)

We investigated changes of thiols (GSH, GSSG, and cysteine) induced by transplasma membrane electron transport after addition of artificial electron accepters and the influence of the thiol level on redox activity. GSH, GSSG, and cysteine content of maize (Zea mays L, cv. Golden Bantam) roots and coleoptile segments was determined by high performance liquid chromatography with a fluorescence detector. GSSG increased after treatment with 0.8 mM diamide, an SH-group oxidizer. GSH level of roots increased after treatment with diamide, while GSH levels of coleoptiles decreased. Incubation of roots with the GSH biosynthesis inhibitor buthionine-D,L-sulfoximine for 6 days lowered the glutathione level up to 80%. However, the GSH/GSSG ratio of maize roots remained constant after treatment with both effecters. The GSH/GSSG ratio and the glutathione level were changed by addition of artificial electron accepters like hexacyanoferrate (III) or hexabromoiridate (IV), which do not permeate the plasma membrane. Hexacyanoferrate (III) reduction was inhibited up to 25% after the cellular glutathione level was lowered by treatment with diamide or buthionine-D,L-sulfoximine. Proton secretion induced by reduction of the electron accepters was not affected by both modulators. The change in glutathione level is different for roots and coleoptiles. Our data are discussed with regard to the role of GSH in electron donation for a plasma membrane bound electron transport system.