Melatonin alleviates drought-induced cotton pollen abortion by improving carbohydrate and energy metabolism in anthers

Drought stress negatively affects cotton pollen fertility, which in turn leads to a decrease in seed number per boll and boll weight. Exogenous melatonin application significantly enhances pollen fertility under drought conditions, while the specific underlying mechanisms remain unclear. A pot experiment was conducted using a cultivar Yuzaomian 9110 under two moisture treatments (soil relative water content at 75 ± 5 % and 45 ± 5 %) with two melatonin concentration (0 and 200 μM) to investigate the effects of exogenous melatonin on the structural traits and physiological metabolism of cotton anthers and its’ relationships with pollen fertility. Results demonstrated the significant impact of drought on anthers development and metabolism, with damage to the anther tapetum and decreased starch and adenosine triphosphate (ATP) contents, subsequently resulting in reduced pollen germination rate, seed number per boll and boll weight. Melatonin application in water-deficit anthers up-regulated the expression of sucrose transporter protein ( GhSWEET55 ) and phosphate sucrose synthetase, promoting sucrose import and synthesis, respectively. However, it also increased sucrose synthase and acid convertase, accelerating sucrose decomposition and reducing its content. Additionally, melatonin application promoted starch accumulation in water-deficit anthers by enhancing activities of adenosine diphosphate glucose pyrophosphorylase and soluble starch synthase, meaning that potential energy storage was increased, which facilitated the formation of pollen fertility. Although melatonin application reduced the expression of pyruvate kinase ( GhPK ) and glucose 6-phosphogluconate dehydrogenase ( GhG6PD ) genes in water-deficit anthers, it up-regulated hexokinase ( GhHXK ) and citrate synthase ( GhCIT ) expression, enhancing ATP content, and ultimately pollen fertility, seed number and boll weight under drought. In summary, exogenous melatonin preserved cotton pollen fertility under drought stress by regulating carbohydrate and energy metabolism, especially enhancing starch and ATP accumulation in anthers. • Melatonin (ME) application increased boll weight due to higher pollen fertility under drought. • ME application prevented tapetum degradation of drought-stressed anthers. • ME application regulated carbohydrate metabolism, with higher starch content under drought. • ME application increased anther ATP to improve pollen fertility under drought.