Changes in Hormonal Balance: A Possible Mechanism of Pre-Sowing Chilling-Induced Salt Tolerance in Spring Wheat

There is a lack of knowledge about factors contributing to the chilling-induced alleviatory effects on growth of plants under salt stress. Thus, the primary objective of the study was to determine whether chilling-induced changes in endogenous hormones, ionic partitioning within shoots and roots and/or gaseous exchange characteristics is involved in salt tolerance of two genetically diverses of wheat crops. For this purpose, the seeds of two spring wheat (Triticum aestivum) cultivars, MH-97 (salt intolerant) and Inqlab-91 (salt tolerant) were chilled at 3 degrees C for 2 weeks. The chilled, hydroprimed and non-primed (control) seeds of the two wheat cultivars were sown in both Petri dishes in a growth room and in the field after treatment with 15 dS m-1 NaCl salinity. Chilling was very effective in increasing germination rate and subsequent growth when compared with hydropriming and control under salt stress. Results from field experiments clearly indicated the efficacy of chilling over hydropriming in improving shoot dry biomass and grain yield in either cultivar, particularly under salt stress. This increase in growth and yield was related to increased net photosynthetic rate, greater potential to uptake and accumulate the beneficial mineral elements (K+ and Ca2+) in the roots and reduced uptake and accumulation of toxic mineral element (Na+) in the shoots of both wheat cultivars when grown under salt stress. Salt-stressed plants of both wheat cultivars raised from chilled seed had greater concentrations of indoleacetic acid, abscisic acid, salicylic acid and spermine when compared with hydropriming and control. Therefore, induction of salt tolerance by pre-sowing chilling treatment in wheat could be attributed to its beneficial effects on ionic homeostasis and hormonal balance. The results presented are also helpful to understand the chilling-induced cross adaptation of plants in natural environments. Moreover, efficacy of pre-sowing chilling treatment over hydropriming suggested its commercial utilization as a low risk priming treatment for better wheat crop production under stressful environments.