6-Benzylaminopurine-dependent starch accumulation is key to drought tolerance in tall fescue subjected to water deficiency.

Abstract

Drought is a natural disaster that exerts considerable adverse impacts on the agricultural sector. This study aimed to investigate the cytokinin-mediated carbohydrate accumulation in the aerial parts of the plant and the roots in four-month-old drought-stressed tall fescue (Festuca arundinacea Schreb.) plants. To achieve this, exogenous treatments containing 50 mM of the synthetic cytokinin 6-Benzylaminopurine (6-BA) were applied prior to the onset of drought stress and every seven days during the 14-day drought stress period. These plants were subjected to varying levels of soil water holding capacity (WHC): 25 ± 5% (severe stress), 50 ± 5% (moderate stress), and 100 ± 5% (control). A range of morpho-physiological, biochemical, and molecular responses were evaluated. Our data suggest that the reduction of starch and the accumulation of water-soluble carbohydrates (WSCs) induced by severe drought stress were mitigated (reduced by half) in the roots and shoots of plants treated with 6-BA under similar drought conditions. This treatment may support plants by promoting the normal storage of energy reserves, thereby enhancing their resilience during subsequent periods of water scarcity. Furthermore, the application of 6-BA facilitates the regulation of carbohydrate accumulation, proline content, and enzymatic activity. 6-BA functions by downregulating the expression of cytokinin oxidase/dehydrogenase genes, particularly FaCKX1 and FaCKX3, and by upregulating the FaIPT8 gene. This mechanism inhibits the degradation of cytokinins and promotes root growth under conditions of severe drought stress. 6-BA reduced FaPIN1 expression during moderate drought stress compared to the corresponding control, indicating that cytokinins can alter auxin transport mechanisms and help plants prioritize growth processes under water scarcity. The application of 6-BA not only serves as an effective sink for enhancing starch accumulation in leaves but also inhibits the expression of the chlorophyll degradation gene (FaSGR), thereby preventing chlorophyll degradation. This dual action aids plants in sustaining their growth and development during episodes of short-term drought stress.

Supplementary information: The online version contains supplementary material available at 10.1007/s12298-025-01559-5.