IAA-induced alteration in growth and photosynthesis of pea (Pisum sativum L.) plants grown under salt stress

The present study investigates the role of foliar application of indole acetic acid (IAA) in mitigating the loss caused by salinity stress in terms of plant growth and leaf characteristics in pea plants (Pisum sativum L. cv. Adi). Potted plants were grown on amended soil (75% soil and 25% farmyard manure), and IAA (0, 15, and 30 mg l(-1)) was applied to 30-day-old plants as foliar spray for 15 days. Three levels of NaCl (0, 50 and 100mM) were then used for salt-stress treatment and pots were watered regularly with 100% field capacity. Two-month-old plants were sampled for recording data on growth measurements, dry mass production, relative water content and leaf characteristics such as pigment concentration, maximum quantum yield of PSII (Fv/Fm), stomatal conductance (gs), net photosynthetic rate (Pn) transpiration rate (E) and water use efficiency (WUE). All these parameters were suppressed under salinity; the effect of salinity was greater on plants receiving no IAA treatment than on those treated with IAA. Of the salt doses used, 100mM NaCl was most effective. IAA application (30mg IAA l(-1)) to plants growing under stress of 50mM NaCl reduced the expected loss by about 13% in leaf area, 20% in number of leaves, 6% in RWC, 47% in root dry mass (DM), 30% in stern DM, 9% in leaf DM, 27% in total DM, 11% in total chlorophyll, 10% in carotenoids, 15% in Fv/Fm, 20% in gs, 15% in Pn,11% in E and 4% in WUE. However, the same IAA concentration, when applied to plants grown under 100mM NaCl stress, reduced the expected loss by about 25% in leaf area, 24% in number of leaves, 12% in RWC, 65% in root DM, 22% in stem DM, 25% in leaf DM, 30% in total DM, 30% in total chlorophyll, 16% in carotenoids, 17% in Fv/Fm, 32% in gs, 19% in Pn, 14% in E and 6% WUE. On the whole, exogenous IAA application significantly reduced the salinity-induced loss by enhancing plant capacity to withstand the salt stress.