Silicon and Gibberellins: Synergistic Function in Harnessing ABA Signaling and Heat Stress Tolerance in Date Palm (Phoenix dactylifera L.)

Date palm is one of the most economically vital fruit crops in North African and Middle East countries, including Oman. A controlled experiment was conducted to investigate the integrative effects of silicon (Si) and gibberellic acid (GA(3)) on date palm growth and heat stress. The exogenous application of Si and GA(3) significantly promoted plant growth attributes under heat stress (44 ± 1 °C). The hormonal modulation (abscisic acid [ABA] and salicylic acid [SA]), antioxidant accumulation, and the expression of abiotic stress-related genes were evaluated. Interestingly, heat-induced oxidative stress was markedly reduced by the integrative effects of Si and GA(3) when compared to their sole application, with significant reductions in superoxide anions and lipid peroxidation. The reduction of oxidative stress was attributed to the enhancement of polyphenol oxidase, catalase, peroxidase, and ascorbate peroxidase activities as well as the upregulation of their synthesis related genes expression viz. GPX2, CAT, Cyt-Cu/Zn SOD, and glyceraldehyde3-phosphate dehydrogenase gene (GAPDH). The results showed the activation of heat shock factor related genes (especially HsfA3) during exogenous Si and GA(3) as compared to the control. Furthermore, the transcript accumulation of ABA signaling-related genes (PYL4, PYL8, and PYR1) were significantly reduced with the combined treatment of Si and GA(3), leading to reduced production of ABA and, subsequently, SA antagonism via its increased accumulation. These findings suggest that the combined application of Si and GA(3) facilitate plant growth and metabolic regulation, impart tolerance against stress, and offers novel stress alleviating strategies for a green revolution in sustainable food security.