ABA-induced alterations in cytokinin homeostasis of Triticum aestivum and Triticum spelta under heat stress

Abstract

Phytohormones from the cytokinin family play an important role in the regulation of plant growth and development from seed germination to senescence. Their collaborative action with abscisic acid contributes to the establishment of adaptive mechanisms, enabling plants to withstand both abiotic and biotic stresses. The successful application of exogenous ABA has proven effective in enhancing cereals' resilience against abiotic factors. This application influences the balance of endogenous phytohormones, thereby regulating growth, development, and yield. We conducted an investigation to explore the effects of priming with ABA solution (106 M) on the growth and endogenous cytokinin homeostasis in two related wheat species Triticum aestivum and T. spelta under the heat stress. Fourteen-day-old plants with seeds soaked in water (C-plants) or ABA solution (ABA+ plants) were subjected to a heat stress treatment (+40°C, 2 h), and subsequently allowed to recover until the 21st day. During heat stress, the shoot biomass of ABA+ plants from the ‘Podolyanka’ winter wheat variety decreased, while the root biomass of ABA+ plants from ‘Frankenkorn’ spelt wheat variety increased. After recovery, ABA+ wheat plants exhibited lower shoot biomass compared to C- plants, while ABA+ spelt plants surpassed the control. Following heat stress, the total cytokinin content in the shoots and roots of 14-day-old ABA+ wheat plants increased by 76.8 % and 313.3 %, respectively. Trans-zeatin-O-glucoside and isopentenyladenine accumulated in the shoots, with their content being 2.8 and 2.6 times higher, respectively, than in non-stressed ABA+ plants. In the roots, levels of trans-zeatin and isopentenyladenine increased, exceeding the values of non-stressed ABA+ plants by 2.8 and 23.3 times, respectively. Upon resumption of normal temperature conditions, the total cytokinin content in the shoots of 21-day-old ABA+ plants was higher than that of non-stressed ABA+ plants (409.5 ± 20.5 ng·g − 1 FW) and C- plants (542.0 ± 27.1 ng·g − 1 FW). However, the cytokinin accumulation in the roots of recovered ABA+ plants did not reach the levels observed in non-stressed ABA+ plants (458.7 ± 22.9 ng·g − 1 FW), but equaled those of C-plants (364.4 ± 18.2 ng·g − 1 FW). In 14-day-old ABA+ spelt plants, heat stress induced a 53.6 % decrease in the total cytokinin content in shoots, while the content in roots increase by 6.4 %. In the shoots of stressed ABA+ plants, trans-zeatin levels increased 39.2 times, while the levels of all other cytokinin forms decreased. In roots, the amount of trans-zeatin and isopentenyladenine increased from trace values to 60.3 ± 3.2 and 182.5 ± 9.1 ng·g − 1 FW, and the content of isopentenyladenosine increased 13.4 times. After recovery on the 21st day the total cytokinin content in ABA+ plants were 2.6 and 2.1 times lower than in non-stressed ABA+ and C-plants, respectively. Overall, priming seeds with ABA solution resulted in differential changes in cytokinin homeostasis between winter wheat and spelt wheat under heat stress. Exogenous ABA induced the cytokinin accumulation in the shoots and roots of ‘Podolyanka’ wheat while in ‘Frankenkorn’ spelt, high temperature caused a decrease in shoot cytokinin content and an increase root cytokinin content. After recovery, the prolonged effect of priming was manifested by an increase in cytokinin levels in winter wheat shoots and a decrease in root levels, while both shoot and root levels declined in spelt wheat. The ABA-induced alterations in cytokinin homeostasis helped alleviate the negative impact of heat stress and provided insight into interplay between these phytohormones in shaping the plant's response to stress.