Studies On Physiological Mechanisms Of Salt Resistance Improved By Silicon In Cucumber

Salinity toxicity is a worldwide agricultural and eco-environmental problem. Silicon isthe second most abundant mineral element in the soil after the oxygen, its uptake has beenwidely found to be beneficial in improving the biotic and abiotic stresses. It has been reportedthat silicon induced the stress tolerance not only through structural activity of a physicalbarrier, but also through the involvement of a metabolic or physiological regulator. In order toclarify the mechanisms of silicon in enhancing plant salt resistance, Cucumis sativus L.cvJinyou NO.1were grown in the hydroponic solution with silicon and NaCl. The effects ofsilicon on growth, photosyntheisis, osmotic adjustment, ion accumulation, activities of majorantioxidant enzymes and polyamines accumulation in cucumber seedlings were investigated.And then we got these results as following:1. Application of silicon alone had no effects on cucumber growth, while it partlyreversed the salt-induced reduced in plant growth, chlorophyll content, photosynthesis,stomatal conductance and transpiration.2. In non-saline media, there was no effect of supplementary silicon on the osmoticpotential and osmolytes. The osmotic potential of silicon application was lower at beginningof salt stress, then became higher than salt alone application. Meanwhile, the osmolytes,especially, the sucrose levels, but not the proline, were significantly increased than thatwithout silicon application under salt stress. The soluble protein content was not affected bysilicon application.3Application of silicon alone had no effects on cucumber water situation, while it partlyreversed the salt-induced reduced in plant transpiration, root hydraulic conductance, water useefficiency and leaf water content.4. In normal condition, silicon had no effects on ion content of cucumber leaves. Na+concentration was increased while K+concentration and K+/Na+ratio were decreased insalt-treated plants. While, this tendency was partly reversed by silicon application, especiallyin the leaves.5. Under salt stress, SOD、CAT activities decline and APX、POD activities increase inplants and malondialdehyde (MDA) accumulates rapidly, which results in an increase in permeability of plasma membranes. The activities of SOD, CAT,APX and POD in leaves ofsalt-stressed cucumber were significantly increased by silicon, while MDA accumulation wasdecreased by silicon.6.In normal condition, silicon had no effects on polyamines accumulation in cucumberleaves. However, salt significantly reduced the content of free polyamines and had acomplicated influence on insoluble polyamines, while silicon application promoted theaccumulation both free polyamines and insoluble polyamines.It can be concluded that silicon application not only decreases Na+toxicity and improvesthe water status in plant, but also increases polyamines content and improve activities ofmajor antioxidant enzymes which allows a higher photosynthesis and growth rate, lead to salttolerance. Osmotic adjustment, which has little effect at the beginning of salt stress, is not themain factor of silicon improving the salt tolerance.