The possible involvement of activated oxygen species in the mechanism
of damage by NaCl stress was studied in leaves of four varieties of ri
ce (Oryza sativa L.) exhibiting different sensitivities to NaCl. The 3
-week-old rice seedlings were subjected to 0, 6 and 12 dS m(-1) salini
ty levels for 1-week after which differences in antioxidant capacities
and possible correlation, growth rate and Na+ uptake of the leaves we
re analyzed. High salinity treatment caused a decrease in growth rate
in all the varieties tested except Pokkali. The salt-sensitive varieti
es, Hitomebore and IR28, exhibited a decrease in superoxide dismutase
activity and an increase in peroxidase activity under high salinizatio
n. These varieties also exhibited increase in lipid peroxidation and e
lectrolyte leakage as well as higher Na+ accumulation in the leaves un
der salt stress. The salt-tolerant variety Pokkali however, showed onl
y slight increase and decrease in superoxide dismutase and peroxidase
activity, respectively, and virtually unchanged lipid peroxidation, el
ectrolyte leakage and Na+ accumulation upon salinization. On the other
hand, the putative salt-tolerant Bankat variety, which showed a sligh
t stimulation in growth rate similar to Pokkali at moderate salinity l
evel, exhibited Na+ accumulation and symptoms of oxidative damage duri
ng salt stress similar to the salt-sensitive varieties rather than the
salt-tolerant one. These results indicate that free radical-mediated
damage of membrane may play an important role in the cellular toxicity
of NaCl in rice seedlings and that salt-tolerant varieties exhibit pr
otection mechanism against increased radical production by maintaining
the specific activity of antioxidant enzymes. (C) 1998 Elsevier Scien
ce Ireland Ltd. All rights reserved.