Drought‐induced osmotic adjustment and changes in carbohydrate distribution in leaves and flowers of cotton (Gossypium hirsutum L.)

Research has indicated osmotic adjustment as a mechanism by which leaves and roots of cotton plants overcome a drought period. However, the relevance of this mechanism in reproductive tissues of modern cultivars under drought has not been fully investigated. The objectives of this study were to measure osmoregulation and carbohydrate balance in reproductive tissues and their subtending leaves grown under water‐deficit conditions. Two cotton cultivars were grown under controlled environment and field conditions. Plants were exposed to water‐deficit stress at peak flowering, approximately 70 days after planting. Measurements included stomatal conductance, proline concentration, soluble carbohydrates and starch concentration, and water potential components. Stomatal conductance of drought‐stressed plants was significantly lower compared to control, while osmotic adjustment occurred in reproductive tissues and their subtending leaves by different primary mechanisms. Pistils accumulated higher sucrose levels, maintaining cell turgor in plants exposed to drought at similar levels to those in well‐watered plants. However, subtending leaves lowered osmotic potential and maintained cell turgor by accumulating more proline. Soluble carbohydrates and starch concentration in leaves were more affected by drought than those of floral tissues, with corresponding reduction in dry matter, suggesting that flowers are more buffered from water‐deficit conditions than the adjacent leaves.