Comparison of cadmium-induced iron-deficiency responses and genuine iron-deficiency responses in Malus xiaojinensis

The effects of the heavy metal Cd in Malus xiaojinensis were investigated using hydroponic cultures. Chlorophyll and Fe concentrations in young leaves were markedly decreased by Cd treatment, although Fe concentration was significantly enhanced in the roots. A comparative examination of the Fe-deficiency responses due to Fe deficiency and Cd treatment was also performed. Both Fe deficiency and Cd treatment induced responses similar to those of Fe-deficiency in M. xiaojinensis, including acidification of the rhizosphere, enhanced Fe(III) chelate reductase activity, and upregulation of the Fe-deficiency-responsive genes MxIRT1 and MxFRO2-Like. However, the Fe-deficiency responses induced by Cd treatment were different in intensity and timing from those induced by Fe deficiency.