Dose-dependent responses of Arabidopsis thaliana to zinc are mediated by auxin homeostasis and transport

Zinc is an essential element for plant; however, in excess it could cause adverse effects on plant growth and productivity. Plants have evolved various regulatory mechanisms to optimize their growth and development at different zinc concentrations. In this work, we elucidated the role of auxin homeostasis and transport in the dose-dependent responses to zinc in Arabidopsis thaliana. The results showed that zinc had dose-dependent effects on both vegetative and reproductive growth of Arabidopsis. At the concentration of 50, 100 and 350 μM, zinc significantly affected the length of primary root and the size of root meristem. This root response to Zn were associated with differentially regulation of endogenous auxin, as demonstrated by the DR5:GUS reporter line and in vivo hormone measurements. Exogenous IAA could alleviate the Zn-induced short-root phenotype by affecting auxin accumulation in plants, while Arabidopsis mutants with deficient auxin synthesis or transport mechanisms exhibited hypersensitivity to Zn. In conclusion, the effect of zinc on root growth of Arabidopsis thaliana is regulated by differences in auxin synthesis and transport.