Imbalance of redox homeostasis and antioxidant defense status in maize under chromium (VI) stress

The present study assesses the toxicity of hexavalent chromium [Cr(VI)] on maize (Zea mays L.) seedlings. Three different levels of Cr stress [50, 100 and 200 mg/l CrO3] were imposed and maize seedling growth performances were monitored at 2d and 4d. Modulation of antioxidant genes expression, metabolites, membrane damage, in vivo ROS detection, foliar H2O2 and proline accumulation were studied in detail to get an overview of Cr stress response of maize. Prime stress responses included marked reduction in plant height and biomass, loss of root cell viability with decreased APX-1, Cu/Zn SOD and DHAR expression and high accumulation of Cr in roots with little translocation to shoots. Higher uptake of Evans blue by Cr challenged roots indicates loss of root cells viability. In vivo detection of superoxides and H2O2 as dark blue and deep brown spots in stressed leaves supported with CM-H2DCFDA and DHE staining of roots strongly suggest severe oxidative burst under Cr stress. Marked decline in MDAR and DHAR expression in 200 mg/l Cr challenged leaves at 4d with non-significant change in AsA/DHA ratio indicate futile recycling of ascorbate pool which might lead to disturbance in redox homeostasis. Isolated increase in GR expression coupled with high GSH/GSSG do not seem to prevent cells from oxidative damages, as evident from high foliar MDA level in Cr challenged seedlings. Moreover, enhanced proline accumulation in maize leaves does not give much protection against Cr stress. Over all, this study facilitates our understanding of the plants adaptive mechanisms to Cr stress.