Effect of Exogenous Application of IAA. BRs and GA3 on Growth Protein Contents and Antioxidative Enzyme Activities in Solanumtuberosuml. Under Salt Stress.

Abstract

The present study aimed at determining the effect of exogenous application of plant growth regulators (BRs, IAA and GA3) on growth and biochemical activities (total soluble proteins, supeoxide dismutase and peroxidase) of potato (cvs. Cardinal and Desiree) under salinity stress. The concentrations of NaCl (40, 60 or 80 mM) were selected based on pilot experimentation. The method of exogenous application (pretreatment or in medium) and suitable concentrations of above-mentioned phytohormones effective in stimulating plant growth were determined after pilot experiments. For this, the nodal explants from both the cultivars were pretreated for 24 h with different concentrations of EBR (2 or 3 µM) and then inoculated in MS basal medium. On the other hand, EBR (2 or 3 µM) was directly added to the MS medium. After 30 d, data were collected for both the morphological as well as biochemical parameters. It was observed that lower concentration of EBR was more effective in enhancing morphological growth of both the cultivars. Likewise, the concentrations of IAA (7, 14 or 21 µM) and GA3 (7, 14 or 21 µM) were also used with both methods of treatment in cvs. Cardinal and Desiree. The results indicated that lower concentrations of IAA and higher concentrations of GA3 influence growth more effectively. To study the effect of IAA (7 or 14 µM) and GA3 (14 or 21 µM) under salt stress, both ways of pretreatment (PT and IM) were carried out and the nodal explants were grown in MS medium supplemented with the selected NaCl concentrations. The results indicated deleterious effects of NaCl on the morphological growth parameters (root number/length, shoot number/length, number of nodes/leaves, fresh weight) of the two tested cultivars, however, exogenous application of both IAA and GA3 enhanced the growth of plants under stress. The total soluble proteins and activities of SOD and POD were also increased when either NaCl or IAA/GA3 were applied alone or in combination. It was also observed that IAA had a positive effect on roots whereas shoot growth was influenced more on exposure to GA3. The effect of both IAA and GA3 supplementation was also studied on callus cultures of both the cultivars growing under salt stress. The results indicated a reduction in fresh weights and morphological growth of calluses under salt stress which, thereby, was improved when either IAA (7 or 14 µM) or GA3 (14 or 21 µM) was added in the callus induction medium. Pot experiments were also performed to investigate the effect of IAA and GA3 on growth of potato tubers under salinity. For this, the tubers were pretreated with either IAA or GA3 for 2 h and then grown in soil, however, after 30 d of germination, the non treated tubers were foliarly sprayed with either IAA or GA3. NaCl stress impeded the growth of both the tested cultivars which was improved through exogenous application of both the growth regulators. Total proteins and activities of SOD and POD were also increased on application of either NaCl or IAA/GA3. In this study, pretreated potato tubers were able to tolerate stress more effectively than foliarly sprayed plants. Another study was carried out to determine the role of BRs (SSBL and EBR) under salinity stress. NaCl stress reduced the growth of both the cultivars which thereby improved when SSBL (1 or 2 µM) was added directly into the medium. Mixed results were observed for root number/length, however, other growth parameters i.e. shoot length/number, number of nodes/leaves and fresh weights were increased when SSBL was added under salt stress. Total soluble proteins and activities of SOD and POD were also enhanced with either NaCl or SSBL alone or in combination describing their positive role in tolerance of salt stress through scavenging of ROS. EBR with both methods of exogenous application (PT and IM) also affected growth of both the cultivars positively with or without NaCl stress.