Silicon Alleviates PEG-Induced Water-Deficit Stress in Upland Rice Seedlings by Enhancing Osmotic Adjustment

This study investigates the effect of added silicon (Si, as sodium silicate) on water statusrelated parameters, osmolytes accumulation and gas exchange in the leaves of hydroponically grown upland rice seedlings under polyethylene glycol (PEG-6000)-induced water stress, the aims being to explore whether Si has been involved in osmotic adjustment (OA) in upland rice plants. Fifty-five-day-old seedlings were subjected to 8.5 % (m/v) PEG-6000 treatment without or with 2.5 mm Si for 7 days. The results showed that addition of Si to culture solution could partially improve total, free, and bound water contents in both leaves and roots, which were all decreased under water stress. Application of Si increased water potential (?w) and osmotic potential (?p) in both roots and leaves while maintained higher turgor pressure (?p), in comparison with the plants without Si application. Added Si also stimulated the active accumulation of some osmolytes in both leaves and roots of stressed plants, which suggested enhanced OA ability. Analysis of gas exchange in leaves showed that net photosynthetic rate, transpiration, and water-use efficiency (WUE) were decreased under water stress, whereas application of Si enhanced the photosynthesis and improved the WUE. This study suggests that PEG-induced water stress in rice could be partially alleviated by addition of Si. This alleviative effect was partially attributable to enhanced OA ability by means of active accumulation of osmolytes.