CHANGES IN THE THIOL DISULFIDE REDOX POTENTIAL IN WHEAT LEAVES UPON WATER-DEFICIT/

Regulation of the thiol:disulfide redox potential requires about 30% o f the total respiratory energy in wheat leaves. Drought lowered the en ergy input on regulation of SH/SS equilibrium with a concomitant decre ase in the SH/SS ratio. The decrease in SH content should be attribute d to protein SH since non-protein SH remained unchanged. Acclimation t o drought required more energy for maintenance of the redox potential, despite a lower SH/SS ratio than in the control unaffected leaves. Th e discrepancy between energy input and the protein SH level seems to b e apparent since acclimation resulted in a pronounced increase in tota l SH groups, which were non-accessible for DTNB titration in the nativ e form. The level of reduced glutathione and specific activity of glut athione reductase were significantly elevated in the acclimated water deficient leaves; moreover, the K-m values for GSSG decreased, indicat ing changes in the isoform pattern of the enzyme. Acclimated leaves un der drought required the same energy input for providing SH/SS equilib rium as fully turgid control leaves.