Abstract
In plants, water deficiency can result from a deficit of water from the soil, an obstacle to the uptake of water or the excess water loss; in these cases, the similar consequence is the limitation of plant growth and crop yield. Silicon (Si) has been widely reported to alleviate the plant water status and water balance under variant stress conditions in both monocot and dicot plants, especially under drought and salt stresses. However, the underlying mechanism is unclear. In addition to the regulation of leaf transpiration, recently, Si application was found to be involved in the adjustment of root hydraulic conductance by up-regulating aquaporin gene expression and concentrating K in the xylem sap. Therefore, this review discusses the potential effects of Si on both leaf transpiration and root water absorption, especially focusing on how Si modulates the root hydraulic conductance. A growing number of studies support the conclusion that Si application improves plant water status by increasing root water uptake, rather than by decreasing their water loss under conditions of water deficiency. The enhancement of plant water uptake by Si is achievable through the activation of osmotic adjustment, improving aquaporin activity and increasing the root/shoot ratio. The underlying mechanisms of the Si on improving plant water uptake under water deficiency conditions are discussed.
Highlights
Silicon (Si) is the second most abundant element in soil
Plant water deficiency may result from a shortage of water in soil or from an obstacle to water uptake
We address recent results that are relevant to the Si effect, and assess what they mean for the interpretation of how Si improves plant water status and enables the maintenance of plant water balance under water deficiency condition
Summary
Silicon (Si) is the second most abundant element in soil. Plants generally take up Si in the form of soluble monosilicic acid H4SiO4, which normally ranges from 0.1 to 0.6 mM in the soil solution (Ma and Yamaji, 2006). Several different aspects are involved in Si-improved plants’ resistance to drought or salt stress, including maintenance of nutrient balance, promotion of photosynthetic rate, increasing antioxidant capacity, and sequestration of toxic ions (Ma, 2004; Liang et al, 2007; Sacała, 2009; Zhu and Gong, 2014; Rizwan et al, 2015). Various compounds of Si, including 1–2 mM Na2SiO3, K2SiO3 or H2SiO3, either applied in the soil or the nutrient solution, are showed to improve the water status of plants experiencing drought or salt stress (Romero-Aranda et al, 2006; Sacała, 2009; Liu et al, 2014, 2015).
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