Abstract
Silicon (Si) is an abundant and differentially distributed element in soils that is believed to have important biological functions. However, the benefits of Si and its essentiality in plants are controversial due to differences among species in their ability to take up this element. Despite this, there is a consensus that the application of Si improves the water status of plants under abiotic stress conditions. Hence, plants treated with Si are able to maintain a high stomatal conductance and transpiration rate under salt stress, suggesting that a reduction in Na+ uptake occurs due to deposition of Si in the root. In addition, root hydraulic conductivity increases when Si is applied. As a result, a Si-mediated upregulation of aquaporin (PIP) gene expression is observed in relation to increased root hydraulic conductivity and water uptake. Aquaporins of the subclass nodulin 26-like intrinsic proteins are further involved in allowing Si entry into the cell. Therefore, on the basis of available published results and recent developments, we propose a model to explain how Si absorption alleviates stress in plants grown under saline conditions through the conjugated action of different aquaporins.
Highlights
The uptake of mineral nutrients is regulated by transporters in the root plasma membranes
In Sorghum bicolor L., Si regulated the expression of the plasma membrane intrinsic proteins (PIPs) aquaporins, under short-term salt-stress exposure, which restored the root hydraulic conductance, Lp, lost due to salinity
If the beneficial effects of Si, in both monocotyledons and dicotyledons, are linked to the passage of water through membranes, future studies should concentrate on the influence of Si on aquaporin expression, under abiotic stress conditions
Summary
The uptake of mineral nutrients is regulated by transporters in the root plasma membranes. Even in non-accumulating plants, the presence of Si in nutrient solutions or soils has been reported to be beneficial against abiotic stress (e.g., NaCl; for a review see Zhu and Gong, 2014), but the mechanisms of Si action in relation to water uptake and aquaporins are poorly understood. The improvement of plant salinity tolerance by Si through enhancement of root water uptake, including the regulation of aquaporin activity and gene expression, is discussed.
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