Alleviation of Salt Stress in Solanum tuberosum L. by Exogenous Application of Indoleacetic acid and L-Tryptophan

Salinity is a major abiotic stress factor that limits crop production and is an ever-present threat to agricultural sustainability and world's food security. Plant hormones are known to play critical role in regulating plant response to stress by up-regulating the proteins and antioxidant enzymes. The present study aimed at alleviation of salt stress in potato cv. Cardinal by exogenous application of various concentrations of indoleacetic acid (IAA; 17.142, 22.875 or 28.570 mu M) and its precursor L-tryptophan (0, 1, 5, 10 or 15 mu M) under in vitro conditions. Salt stress was imposed by four NaC1 (0, 40, 60 or 80 mM) concentrations. Two modes of IAA application were tested, i.e., added directly to Murashige and Skoog (MS) medium or pretreatment of nodal explants procured from in vitro-raised potato plants. Tryptophan was added directly into the medium containing various concentrations of NaCl. Results were recorded for morphological (shoot and root length, number of shoots and roots and nodes and fresh weight) and biochemical parameters (protein content, peroxidase and superoxide dismutase activities) after 30 days of NaCl and IAA/tryptophan treatment. Salinity caused significant reduction in all growth parameters as well as in all biochemical attributes. Exogenously applied IAA and L-tryptophan alleviated these detrimental effects of salinity by enhancing potato growth, protein content and antioxidant enzyme activities in normal as well as NaCl-stressed plants. Direct incorporation of IAA into the medium was found to be a better approach as compared to its pretreatment to the nodal explants. This study has shown up-regulation of proteins, POD, and SOD activities by using IAA and L-tryptophan indicating their possible involvement in the scavenging process of reactive oxygen species in potato growing under salt stress.