Leaf morpho-anatomical traits regulate the differential responses of stomatal and mesophyll conductance to drought in...

Drought poses a significant threat to global rice production, and a comparative study between rice and wheat serves as an essential approach to unravel the mechanisms relating to drought tolerance. This study examined the differential responses of gas exchange, leaf hydraulic conductance, and leaf morpho-anatomical traits in Shanyou 63 (Oryza sativa) and Yannong 19 (Triticum aestivum). Our findings revealed that rice photosynthesis was more sensitive to drought than wheat, primarily due to greater reductions in stomatal conductance (g_s) and mesophyll conductance (g_m). The larger reduction of g_s in rice was related to a more substantial decrease in leaf hydraulic conductance, which was driven by more severe downsizing of leaf xylem conduits and the thickened mestome cell walls. The more severe depression of g_m in rice under drought was associated with the decreased chloroplast surface area exposed to intercellular airspaces and cell wall porosity (φ/τ) as well as the thickened mesophyll cell walls (T_cw-mes). The thicker T_cw-mes and the decreased φ/τ may be related to the biosynthesis and deposition of cellulose and hemicellulose. This study provides evidence that the regulation of cell wall components and the retention of leaf morphological and anatomical structures play a critical role in maintaining a high photosynthetic capacity under drought stress.