Osmolyte modulated enhanced rice leaf catalase activity under salt-stress

Change in catalase activity was examined in leaves of rice plant exposed to salinity. Depending on the method of preparation of crude protein extract from leaf and the constituents of the assay medium, a significant difference in enzyme activity was recorded. Inclusion of sorbitol or mannitol or sucrose in the extraction and enzyme assay medium enhanced the enzyme activity in salt-stressed samples by nearly 1.5-1.8 fold, compared to the activity found in unstressed plants, which otherwise showed a 50% declined activity in leaf extract prepared in buffer solution and assayed in a medium depleted of these sugars. In view of the accumulation of osmolytes under saline condition, these observations suggest that the catalase activity is modulated by the osmolytes and maintains a high rate of hydrogen peroxide scavenging property in vivo and serves as the major antioxidant enzyme to scavenge the salt-induced formation of peroxide. Therefore, the salt-stress induced appearance of low activity of the enzyme under normal buffer extraction and assay conditions, as reported in literature may represent an apparent than for its real in vivo activity.