ANTIOXIDANT DEFENSES AGAINST ACTIVATED OXYGEN IN PEA NODULES SUBJECTED TO WATER-STRESS

The involvement of activated oxygen in the drought-induced damage of p ea (Pisum sativum L. cv Frilene) nodules was examined. To this purpose , various pro-oxidant factors, antioxidant enzymes and related metabol ites, and markers of oxidative damage were determined in nodules of we ll-watered (nodule water potential approximately -0.29 MPa) and water- stressed (nodule water potential approximately -2.03 MPa) plants. Wate r-stressed nodules entered senescence as evidenced by the 30% decrease in leghemoglobin and total soluble protein. Drought also caused a dec rease in the activities of catalase (25%), ascorbate peroxidase (18%), dehydroascorbate reductase (15%), glutathione reductase (31%), and su peroxide dismutase (30%), and in the contents of ascorbate (59%), redu ced (57%) and oxidized (38%) glutathione, NAD(+) and NADH (43%), NADP( +) (31%), and NADPH (17%). The decline in the antioxidant capacity of nodules may result from a restricted supply of NAD(P)H in vivo for the ascorbate-glutathione pathway and from the Fe-catalyzed Fenton reacti ons of ascorbate and glutathione with activated oxygen. The Ir-fold in crease in the content of ''catalytic Fe'' would also explain the augme nted levels of lipid peroxides (2.4-fold) and oxidatively modified pro teins (1.4-fold) found in water-stressed nodules because of the known requirement of lipid and protein oxidation for a transition catalytic metal.