Silicon Affects Transcellular and Apoplastic Uptake of Some Nutrients in Plants

The positive effects of silicon (Si) on growth of plants have been well documented; however, the impact of Si on plant nutrient uptake remains unclear. The growth, nutrient content and uptake of wheat (Triticum aestivum L.), canola (Brassica napus L.) and cotton (Gossypium hirsutum, L.) plants were evaluated with or without application of 1.5 mmol L-1 Si. Application of Si increased dry weights by 8%, 30% and 30% and relative growth rate (RGR) by 10%, 13% and 17% in the cotton, canola and wheat plants, respectively. The plant relative water content (RWC) was also increased, but the plant transpiration was decreased by Si application. The uptake and content of Ca2+ were 19% and 21% lower in the cotton and wheat plants with Si than those without Si, respectively; however, Si application increased both K+ and Fe uptake and contents in all plant species. Silicon application reduced B uptake and content only in cotton and increased P and Zn2+ contents in all three plant species. The decrease in Ca2+ uptake by Si application was sustained even in the presence of metabolic inhibitors 2,4-dinitrophenol and sodium cyanide. Uptake of Ca2+ by Si application was enhanced or did not change when plant shoots were saturated with water vapor or their roots were exposed to low temperature. Thus, Si application increased the uptake of transcellularly transported elements like K+, P, Zn2+ and Fe. In contrast, Ca2+ uptake which occurred via both apoplastic and transcellular pathways was decreased by Si application, possibly through reduction of apoplastic uptake. More efficient nutrient uptake might be another promoting effect of Si on plant growth.