Differential response of rice seedlings to salt stress in relation to antioxidant enzyme activity and membrane stability index

Three rice genotypes, IR 74802, IR 73104 and IR 72593, along with FL 478 and IR 29 as resistant and susceptible controls, respectively, were subjected to 21 days' salinity stress at the seedling stage in modified yoshida solution with two salt levels (60 and 120mM NaCl). The results indicated that there was a profound increase in proline and ascorbic acid levels, and in the activity of nitrate reductase and antioxidant enzymes, i.e. catalase, peroxidase and ascorbate peroxidase, as well as malondialdhyde and membrane stability index, which were associated with salt tolerance. Salt stress had a significant and drastic effect on all parameters when the salinity level increased to 120mM NaCl. The increased enzyme activity was directly related to an increased membrane stability index, as in IR 72593, which is identified as the most tolerant among the genotypes tested. It is clearly confirmed that predicting tolerance at the early seedling stage is the best way to assess the salinity tolerance level by utilizing physiological parameters, especially antioxidant enzyme activities which are found to be closely associated with salinity tolerance. Physiological adaptation of the plant to NaCl salt stress resulted in enhanced activity of stress-related enzymes and low sodium uptake in tolerant genotypes.