The Role of Silicon in Higher Plants under Salinity and Drought Stress

Abstract

Although deemed a "non-essential" mineral nutrient, silicon (Si) is clearly beneficial to plant growth and development, particularly under stress conditions, including salinity and drought. Here, we review recent research on the physiological, biochemical, and molecular mechanisms underlying Si-induced alleviation of osmotic and ionic stresses associated with salinity and drought. We distinguish between changes observed in the apoplast (i.e., suberization, lignification, and silicification of the extracellular matrix; transpirational bypass flow of solutes and water), and those of the symplast (i.e., transmembrane transport of solutes and water; gene expression; oxidative stress; metabolism), and discuss these features in the context of Si biogeochemistry and bioavailability in agricultural soils, evaluating the prospect of using Si fertilization to increase crop yield and stress tolerance under salinity and drought conditions.

Keywords: apoplast; drought stress; ion transport; osmotic stress; salinity stress; silicon; sodium toxicity; water transport.

FIGURE 1

Contrasting responses of plant Na⁺ fluxes to Si. In pre-labeled roots of intact rice seedlings, ²⁴Na⁺ efflux shows no difference in plants grown with or without Si in the presence of high salinity (main panel; redrawn from Malagoli et al., 2008). By contrast, Na⁺ fluxes from root to shoot are highly sensitive to Si supply (inset; redrawn from Gong et al., 2006).