Photosynthetic Physiological Mechanisms of Leaf and Sheath Organs to Drought Stress in Water-Saving and...

Water-saving and drought-resistant rice (WDR) achieves drought resistance and stable yield by maintaining high photosynthetic potential in leaves under severe drought. We speculated that the sheath organ serving as a photosynthetic source can contribute to a positive response to drought in WDR. However, the synergetic photosynthetic adaptation mechanisms of leaf and sheath organs to drought remain unknown. In this study, a pot experiment was conducted to investigate the WDR of Hanyou73 (HY73) and its parents, Hanhui3 (HH3) and Huhan7A (HH7A). All varieties were subjected to drought at heading with -100 kPa soil water potential. The results demonstrated that chlorophyll content, relative water content, photosynthesis-related parameters, and sugar contents of leaf and sheath organs were significantly reduced during drought across three varieties. However, the activities of catalase and peroxidase and the contents of proline, hydrogen peroxide, and abscisic acid increased during drought treatment in leaf and sheath organs of all varieties. The stomatal conductance changed less in the sheath organ than in the leaf organ under drought stress. Further analyses revealed that stomatal conductance in leaf and sheath organs was mainly regulated by large stomatal apertures among anatomical structural characteristics of stomata across varieties and treatments. For HY73, high drought resistance was associated with a high sucrose-supplying capacity, resulting from high photosynthetic potential in leaf and sheath organs, which was achieved by improving stomatal aperture compared to its parents. This study provides a theoretical basis for the mechanism of photosynthetic adaptation of leaf and sheath organs, synergistically improving drought resistance in rice.