Photorespiration and photoprotection of grapevine (Vitis vinifera L. cv. Cabernet Sauvignon) under water stress

In order to investigate the photoprotective function of photorespiration in grapevine under water stress, potted grapevines (Vitis vinifera L. cv. Cabernet Sauvignon) were randomly divided into three uniform groups for well-watered [watered every morning to keep the relative water content (RWC) of soil over 70 %], water-stress adapted (drought-adapted at 30 % relative soil water content for 30 days), and water stress without adaptation treatment (water-stressed to 30 % relative soil water content for 3 days). Net assimilation rate (A (N)), stomatal conductance (g (s)), substomatal CO2 concentration (C (i)), transpiration rate (E), actual photochemical efficiency of PSII (I broken vertical bar(PSII)), and maximum photochemical efficiency of PSII (F-v/F-m) were recorded by combining measurements of gas exchange and chlorophyll fluorescence. Gross photorespiration (P-r), photosynthetic electron partitioning (J(C)/J(T)), photochemical quenching coefficient (qP), and non-photochemical quenching (NPQ) were also calculated. The ratio of net assimilation rate to transpiration rate (A (N)/E) was used as an indicator of water use efficiency (WUE). A (N), apparent P-r, I broken vertical bar(PSII), F-v/F-m, qp, and g (s) decreased, NPQ increased, and gross P-r sustained at a high level under water stress. This suggests that both photorespiration and energy dissipation play important roles in protecting photosynthetic apparatus against photoinhibition. C (i) in water-stressed plants without adaptation treatment increased, which indicates the leaves suffered a non-stomatal limitation, while the water-stress adaped plants only suffered a stomatal limitation indicated by low C (i).