Zinc deficiency tolerance in maize is associated with the up-regulation of Zn transporter genes and antioxidant activities

Zinc (Zn) is an essential micronutrient for the growth and development of plants. However, Zn deficiency is a common abiotic stress causing yield loss in crop plants. This study elucidates the mechanisms of Zn deficiency tolerance in maize through physiological and molecular techniques. Maize lines tolerant (PAC) and sensitive (DAC) to Zn deficiency were examined physiologically and by atomic absorption spectrometry (AAS). Proteins, H2O2, SOD, POD, membrane permeability and gene expression (using real-time PCR) of roots and shoots of both maize lines were assessed. Zn deficiency had no significant effect on root parameters compared with control plants in PAC and DAC but showed a substantial reduction in shoot parameters in DAC. AAS showed a significant decrease in Zn concentrations in both roots and shoots of DAC but not PAC under Zn deficiency, implying that Zn deficiency tolerance mechanisms exist in PAC. Consistently, total protein and membrane permeability were significantly reduced in DAC but not PAC in both roots and shoots under Zn deficiency in comparison with Zn-sufficient plants. Real-time PCR showed that expression of ZmZIP1, ZmZIP4 and ZmIRT1 transporter genes significantly increased in roots of PAC, but not in DAC due to Zn deficiency compared with controls. The H2O2 concentration dramatically increased in roots of DAC but not PAC. Moreover, tolerant PAC showed a significant increase in POD and SOD activity due to Zn deficiency, suggesting that POD- and SOD-mediated antioxidant defence might provide tolerance, at least in part, under Zn deficiency in PAC. This study provides an essential background for improving Zn biofortification of maize.