Bicarbonate affects the expression of iron acquisition and translocation genes involved in chlorosis in Medicago lupulina

Iron (Fe) deficiency chlorosis (FDC) in plant is associated with high bicarbonate concentration in calcareous soil and irrigation water, which leads to new leaf yellowing and lessens crop yield and quality. However, little is known about whether the chlorosis under bicarbonate stress resulted from blocking root–shoot Fe translocation or root Fe absorption. Moreover, the molecular response of chlorotic leaf under bicarbonate stress has been rarely reported on. The purpose of this study was to investigate the effect of bicarbonate on Fe acquisition, Fe translocation as well as Fe accumulation in roots, normal leaf (NL) and chlorotic leaf (CL) of Medicago lupulina. Seeds were grown with and without Fe and NaHCO₃ (Fe and Bic) in the nutrient solution for 10 d. Fe content, gene expression and enzymatic activity in different tissues were determined. A factorial statistical design with two factors (Fe and Bic) and two levels of each factor was adopted: + Fe, −Fe, + Fe + Bic and −Fe + Bic. Results indicated that bicarbonate stress increased the expression of genes MlHA1, MlFRO1 and MlIRT1 related to Fe acquisition and promoted the Fe absorption from solution. Furthermore, the presence of bicarbonate stress inhibited the expression of MlMATE66 in roots, prevented the Fe translocation from roots to developing leaf, brought about Fe accumulation in roots and reduced the Fe content in new leaf. Generally, according to our results, bicarbonate could prevent Fe translocation from roots into developing leaf, decrease Fe bioavailability and induce chlorosis in M. lupulina.