Water-deficit tolerance in citrus is mediated by the down regulation of PIP gene expresión in roots

Abstract

Water deficit (WD) is a growing problem in agriculture. In citrus crops, genetically-determined characteristics of the rootstock are important factors in plant responses to WD. Aquaporins are involved in regulating the water supply to the plant by mediating water flow through the cell membranes. Recent studies support a direct role for aquaporins in plant water relations and demonstrate their involvement in tolerance to WD. This study investigates the relationship between photosynthetic and water-balance parameters with levels of expression of aquaporins in conditions of moderate WD in the rootstocks Poncirus trifoliata (L.) Raf. (PT), Cleopatra Mandarin (Citrus reshni Hort. ex Tan.) (CM) and 030115 (a hybrid of the two former rootstocks). Under conditions of WD, the hybrid 030115 drastically reduced aquaporin expression, accompanied by a loss of plant vigour but without reducing the net CO2 assimilation (ACO2). PT maintained the same level of aquaporin expression under WD as under normal irrigation conditions, but suffered a sharp reduction in ACO2. CM, which has lower expression of aquaporins than PT under both normal irrigation conditions and WD, responded better to water stress conditions than PT. Thus, low levels of aquaporins, or repression of their expression, accompanied by decreased plant vigour resulted in a decrease in plasma membrane permeability, thereby facilitating water retention in the cells under conditions of water stress. This can induce water stress tolerance in citrus rootstocks.