No abstract

This study investigates the effect of added silicon (Si, as sodium silicate) on water status–related 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 (Ψw) and osmotic potential (Ψπ) in both roots and leaves while maintained higher turgor pressure (Ψp), 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.

The present study assesses the effects of 5‐aminolevulinic acid (ALA, 0, 0.1, 1 and 10 mg l−1) on the growth of oilseed rape (Brassica napus L. cv. ZS758) seedlings under water‐deficit stress induced by polyethylene glycol (PEG 6000, 0 and −0.3 MPa). Water‐deficit stress imposed negative effects on seedling growth by reducing shoot biomass, cotyledon water potential, chlorophyll content and non‐enzymatic antioxidants (glutathione and ascorbic acid) levels. On the other hand, water‐deficit stress enhanced the malondialdehyde (MDA) content, reactive oxygen species (ROS) production, enzymatic antioxidants activities, reduced/oxidized glutathione ratio (GSH/GSSG) and reduced/oxidized ascorbic acid (ASA/DHA) ratio in seedlings. Application of ALA at lower dosages (0.1 and 1 mg l−1) improved shoot weight and chlorophyll contents, and decreased MDA in rape seedlings, whereas moderately higher dosage of ALA (10 mg l−1) hampered the growth. The study also indicated that 1 mg l−1 ALA improved chlorophyll content, but reduced MDA content and ROS production significantly under water‐deficit stress. Lower dosages of ALA (0.1 and 1 mg l−1) also enhanced GSH/GSSG and ASA/DHA as compared to the seedlings under water‐deficit stress. The antioxidant enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase and superoxide dismutase) enhanced their activities remarkably with 1 mg l−1 ALA treatment under water‐deficit stress. It was also revealed that 1 mg l−1 ALA treatment alone induced the expression of APX, CAT and GR substantially and under water‐deficit stress conditions ALA treatment could induce the expression of POD, CAT and GR to a certain degree. These results indicated that 0.1–1 mg l−1 ALA could enhance the water‐deficit stress tolerance of oilseed seedlings through improving the biomass accumulation, maintaining a relative high ratio of GSH/GSSG and ASA/DHA, enhancing the activities of the specific antioxidant enzymes and inducing the expression of the specific antioxidant enzyme genes.