Potassium ameliorates iron deficiency by facilitating the remobilization of iron from root cell walls and promoting its translocation from roots to shoots

Background and aims Iron (Fe) is a vital microelement, and is beneficial for living organisms. Several studies have demonstrated that ample supplied of potassium (K) can alleviate Fe-deficiency-induced chlorosis in plants. In this work, the mechanism underlying K-mediated amelioration of Fe deficiency in Arabidopsis was investigated. Methods Five-week-old Arabidopsis thaliana (Col-0) plants with similar sizes were grown either on complete nutrient solution (+Fe+K) or lacking of K (+Fe-K) or lacking of Fe (-Fe+K), or lacking both of Fe and K (-Fe-K) for 4 days:. The plants were then harvested, and their Fe content, soluble Fe content, phenolic compounds content, Fe translocation and uptake-related genes expression levels, polysaccharides concentration were analyzed, moreover, we also determined the pectin methylesterase activity and its methylation. Results Under Fe deficiency, K-deficient plants accumulated higher amounts of root apoplastic Fe along with a higher Fe content in pectin and hemicellulose 1, and which was rapidly decreased when K was included in the nutrition solution, indicating the operation of a cell wall Fe-remobilization mechanism. Under Fe-deficient condition, K supply significantly increased the secretion of phenolic compounds and the degree of pectin methylation, while decreased pectin and hemicellulose 1 contents as compared with -Fe-K, thereby promoting Fe reutilization from root cell walls. Furthermore, K supply also enhanced the reutilization of Fe from vacuoles through up-regulation of AtNRAMP3 expression. In addition, K supply stimulated several genes associated with long-distance transport of Fe expression, including AtFRD3, AtYSL2, and AtNAS1, suggesting ample K supply can enhance Fe transportation from roots to leaves. Conclusions Stimulation of Fe reutilization from cell walls and vacuoles, as well as an enhancement of Fe transportation from roots to leaves were the major mechanism underlying K-mediated amelioration of Fe-deficiency in Arabidopsis plants.