Evaluation of salt tolerance in rice (Oryza sativa L.) under in vitro conditions

We attempted to study the response of six rice cultivars, viz., BPT 5204, CR 1009, TRY 1, CO 50, Jodimattai, and CO 46, to salt stress under in vitro conditions. In this study, we report the highest relative growth rate (RGR) in BPT 5204 and TRY1, suggesting that these could maintain a higher relative fresh mass of the callus to survive salt stress. For regeneration frequency (RF), genotype TRY 1 registered the highest RF (35%) in the control (0 mM NaCl), but a significant reduction in RF (66%) was observed at 90, 120, and 150 mM NaCl. The genotypes CO 50, CR 1009, and BPT 5204 registered the lowest regeneration frequency (6.7%) and produced a moderate number of shoots. The biochemical nature of stress implies that proline content decreases in the control and progressively increases from 30 to 90 mM but gradually decreases with higher salt concentrations. The proline content was high for both tolerant (BPT 5204) and sensitive (CO-46) cultivars, implying that proline gives adaptiveness rather than growth. Our results provide unique insight into the antioxidant (catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD)) properties of callus culture. Antioxidants act as potential reactive oxygen species (ROS) scavengers and provide adaptive mechanisms to plants. The antioxidant enzyme activities increased progressively with increasing NaCl concentration in the medium, showing that antioxidants augment the stress and provide an adaptive mechanism. The genotypes BPT 5204 and TRY1 had a significant level of enzyme activities at 90, 120, and 150 mM NaCl treatment, whereas the other genotypes seemed to have reduced enzymatic activities. Hence, the genotypes BPT 5204 and TRY1 were better in their performance for the above parameters, which showed growth and biochemical homeostasis in response to salt stress.