Exogenous application of abscisic acid regulates endogenous gibberellins homeostasis and enhances resistance of oriental melon (Cucumis melo var. L.) against low temperature

We analyzed the possible effect of abscisic acid (ABA, 5 and 10 μM), jasmonic acid (JA, 20 and 40 μM) and salicylic acid (SA, 20 and 40 μM) treatments on counteracting the adverse impacts of low temperature on oriental melon. Results of this first experiment showed that shoot and root length, fresh weight, and stem diameter of melon plants under chilling conditions, were significantly improved in response to 5 and 10 μM ABA applications as compared with control and other hormone treatments. Hereafter, in a second experiment 3 ABA concentrations, 1, 3, and 5 μM were assayed to find out optimum dose and 3 μM was found to have the highest effect. Then, the leaves of the 3 μM ABA treated plants were used to study the gibberellic acid (GA) homeostasis after 1, 3, 5 and 7 days of treatments, as well as to determine their internal concentration of SA. The results showed that oriental melon contains bioactive GAs (GA1 and GA4) suggesting the existence of a non-13 hydroxylation pathway. During low temperature stress, GA4 content was significantly increased (approximately 400-fold) 3 days after ABA treatment as compared with the control. In addition, endogenous SA was also significantly increased in ABA treated plants as compared to control plants under stress. In conclusion, our results suggest that exogenous ABA application to oriental melon plant may induce tolerance against low temperature stress by up-regulating the endogenous GA4 and SA.