The regulatory role of silicon on carbohydrate metabolism in Cucumis sativus L. under salt stress

The mechanism for silicon-mediated salt tolerance is still not very clear. The aim of this study was to investigate the possible role of silicon in regulating carbohydrate metabolism in cucumber (Cucumis sativus L.). Two cucumber cultivars ('JinYou 1' and 'JinChun 5') grown hydroponically were subjected to 75 mM NaCl stress in the absence or presence of added silicon (0.3 mM). Plant growth, oxidative damage, chlorophyll fluorescence and carbohydrate metabolism were investigated. Added silicon improved plant growth and photosynthetic performance, while alleviated oxidative damage of cucumber under salt stress. Salt stress increased the soluble sugar levels in both leaves and roots. Starch was accumulated in the leaves but decreased in the roots under salt stress. Added silicon decreased the soluble sugar levels in leaves through regulating the activities of carbohydrate metabolism enzymes. The starch content was decreased in leaves but increased in roots by added silicon under stress. Silicon addition increased the root sucrose content in 'JinYou 1' but decreased it in 'JinChun 5' under salt stress. Silicon-mediated decrease of assimilate accumulation in leaves may alleviate photosynthetic feedback repression, while silicon-enhanced assimilate transport provides more energy storage in the roots, which is beneficial for salt stress tolerance.