Physiological causes for decreased productivity under high salinity in Boma, a tetraploid Chloris gayana cultivar. II. Oxidative stress

In tetraploid cultivars of Rhodes grass (Chloris gayana Kunth) productivity decreases significantly under saline conditions. Two closely related clones of cv. Boma (T and S), exhibiting different degrees of salt tolerance, were compared with determine the physiological causes for such decrease. In those clones, salt tolerance was associated with differences in the proportion of dry leaves, salt gland density, Na excretion rate, and oxidative stress damage. The purpose of this paper is to evaluate whether salt tolerance and oxidative stress development in these clones are related to the activity of two antioxidant enzymes. Experiments were conducted in a greenhouse, in winter and summer, in plants treated with 0, 100, or 200 mm NaCl. In the summer, increases in oxidative damage, as determined by malondialdehyde (MDA) concentration, mirrored decreases in CO2 fixation at high salinity, especially in clone S. In clone T, salinity induced higher increases in Fe-SOD (superoxide dismutase) activity in summer-grown plants, and in ascorbate peroxidase (APX) in winter-grown plants. Oxidative stress induced by low paraquat concentration also induced an increase in Fe-SOD in leaf segments of clone T, and APX was less affected in clone T than in clone S. These results suggest that the clones differ in the control of antioxidant enzymes. Nevertheless, leaf death in winter was not related to increases in MDA, indicating that the association between salinity, leaf senescence and oxidatives stress is also influenced by other factors.