Differential Salt Tolerance Capacity of Kaipad Rice Varieties Evidenced By Enzymatic and Non-Enzymatic Antioxidant System

Soil salinity leads to serious productivity loss by activating a series of metabolic reactions. The static nature of the plants necessitates the activation of complex metabolic activities including antioxidant pathways, especially the scavenging of reactive oxygen species (ROS). In the present study, three rice cultivars, traditionally grown in the Kaipad rice system were selected to characterise their salt tolerance compared to the salt tolerant variety Vytilla-2. The 21 day old seedlings of the Kaipad rice varieties and Vytilla-2 were subjected to salt stress, ranging from 25 mM to 150 mM NaCl. The leaf samples were collected at an interval of 7, 14 and 21 days of salt stress and evaluated for enzymatic and non-enzymatic antioxidants and ascorbate-glutathione cycle enzymes. The specific activity of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) were correlated with the superoxide (O2 -), malondialdehyde (MDA), glutathione (GSH, total and reduced ) and ascorbate (AsA) content using standard protocols. Results indicated that, the variety Ezhome – 1 alleviates salt stress comparable to Vytilla-2, treated with 150 mM NaCl during the 21st day of salt stress, while cultivars Kuthiru and Kuttoosan showed lesser salt tolerance potential comparable to Vytilla-2. The Na+ accumulation was positively correlated with NaCl concentration and reduction in K+ concentration increased the Na+/K+ ratio in all the varieties. Under salt stress the membrane stability index was least affected suggesting the lesser quantity of ion leakage during salt stress. Comparison of salt stress in these varieties suggests the functional cooperation between the antioxidant, ascorbate- glutathione cycle enzymes and nonenzymatic antioxidants to combat the generation of ROS hence promoting their tolerance.