Effect of aluminum on protein oxidation, non-protein thiols and protease activity in seedlings of rice cultivars differing in aluminum tolerance

The effect of toxic concentrations of aluminum (Al) was investigated on contents of protein-thiols, non-protein and total thiols, protein carbonylation and protease activity in the seedlings of Al-sensitive (Al-S) Indica rice cv. HUR-105 and Al-tolerant (Al-T) cv. Vandana grown in sand cultures. Al treatment of 178 μM and 421 μM for 3–12 days caused a significant decline in the level of protein thiols, rise in non-protein thiols (NPTs) as well as protein carbonyl content and an insignificant alteration in the level of total thiols in cv. HUR-105 seedlings. However, in the seedlings of Al-T cv. Vandana, no significant alteration could be observed on any of these parameters with Al treatment. Al treatment inhibited protease activity in roots, whereas the opposite trend was seen in shoots. New isozymes of protease appeared in shoots of cv. Vandana with increased level of Al treatment. Our results show a link between protein thiols and NPTs and suggest the role of NPTs in the repair and protection of protein thiols. Inhibitory effect of Al on protease activity in roots could be a major reason for Al rhizotoxic effects. Al tolerance in rice appears to be associated with lesser content of protein thiols in roots, smaller amount of carbonylated proteins in roots as well as shoots and higher protease activity in shoots.