Plant hydraulic conductivity determines photosynthesis in rice under PEG-induced drought stress

摘要

Photosynthesis ( A ) plays a key role in maintaining plant carbon balance, but it is sensitive to drought. Both A and plant hydraulic conductivity ( K plant ) decrease under water deficit. It is not clearly whether the declined K plant is more related to root or leaf, whether the decreased A is related to K plant and/or leaf hydraulic conductivity ( K leaf ) and diffusive alone or both diffusive and metabolic impairments decreased A . Two drought-tolerant (DW) contrasting rice genotypes were used to explore the relationship of A, K plant and K leaf under PEG induced drought stress (PEG-DS). The results showed that photosynthesis related parameters of A , stomatal conductance (g s ), transpiration rate (Tr), maximum Rubisco carboxylation rate (V cmax ), maximum electron transport rate (J max ), carboxylation efficiency (CE), K leaf , K plant and xylem sap flow rate (XSFR) were all decreased significantly under PEG-DS. These decreases were more severe in DW-sensitive genotype IR64 than DW-tolerant genotype Hanyou-3. However, both intercellular CO 2 concentration (Ci) and CO 2 concentration inside chloroplasts (Cc) were prominently increased in IR64 rather than in Hanyou-3 under PEG-DS. In addition, both g s and g m (mesophyll conductance to CO 2 ) were strongly positively correlated with A (R 2 =0.98 & 0.71). Photosynthesis of both genotypes were increased with increasing Ci under each treatment. Furthermore, A and g s were significantly correlated with K plant (R 2 =0.94 & 0.96) but not with K leaf , and K plant was not related to K leaf . K plant rather than K leaf determines photosynthesis in rice under drought conditions, which was mainly attributed to K plant decreases the stomatal conductance and ultimately lead to decrease in photosynthesis.