Silicon Enhances the Biosynthesis of Organic Acids in Zinc-deficient Rice

Abstract

Zinc (Zn), an essential micronutrient for crops, is involved in a variety of physiological processes. The Zn deficiency mainly affects generative growth and seed development and being a component of the antioxidant machinery (e.g., Cu/Zn-SOD) is conductive to oxidative stress in plant tissues. Rice is a typical silicon (Si)-accumulating species, which is strongly affected by Zn deficiency in the alkaline, low Zn soils, especially high in phosphate and/or organic matter. Yet, little is known about the interaction between Si and Zn in rice plants under Zn-deficient conditions. We investigated the effect of Si nutrition on Zn tissue distribution and biosynthesis of organic acid in rice plants subjected to short-term (up to 7 days) and long-term (28 days) Zn deficiency. Tissue concentrations of organic acids by HPLC in parallel Zn and Si by ICP-OES were measured. The Si addition to the nutrient solution successfully mitigated visual symptoms of Zn-deficiency stress and significantly increased dry biomass of rice plants. Interestingly, during the short-term experiment, +Zn plants supplied with Si showed significantly lower Zn concentration in the shoots, but significantly higher Zn concentration in the roots. Also, in the -Zn plants supplied with Si, the concentration of Zn in root tissue rapidly decreased to the level of -Si/-Zn plants, which was followed by an increased concentrations of both organic acids and Zn in the shoots. In the long-term experiment, however, Si did not affect Zn concentration in roots nor in shoots of -Zn plants, but Si differently affected organic acid profile and their tissue accumulation depending on the plant organ and Zn status. In conclusion, Si supply enhanced root-to-shoot translocation of Zn mediated by organic acid ligands during the first 7 days of Zn deficiency.