Homeostasis of the structurally important micronutrients, B and Si.

This review focuses on recent advances in understanding the transport mechanisms of two elements, B and Si in plants. Both are present as noncharged molecules in soil solution as boric acid and silicic acid. Both function in apoplast: pectic polysaccharides crosslinked with borate and polymers of hydrated silica are important for the physical strength of plant cells. In recent years, molecular genetics revealed analogous transport systems of B and Si. Combinations of NIP channels and exporters localized to distal and proximal sides, allow efficient trans-cellular transport of the nutrients. Polar localization, observed in these transport molecules, is likely to be a key to regulate directional transport of nutrients.