Chilling Sensitivity and Antioxidant Metabolism in Maize (zea Mays L.)

Maize leaves are extremely sensitive to low temperature-induced damage. Chilling results in decreased CO2 assimilation due to loss of key proteins, followed by photoinhibition and photo-oxidation. Destruction of proteins is linked to increased oxidation and activity of proteases. The antioxidant defence system protects the cell against damage from active oxygen species (O2-, H2O2 and 1O2). Differential compartmentation of metabolism (e.g. photosynthesis) and fluxes of metabolites between bundle sheath and mesophyll cells are a feature of C4 metabolism. The distribution of the antioxidants in maize leaves is not uniform: these are compartmented between the bundle sheath and mesophyll according to requirement for and availability of reducing power and NADPH. Dehydroascorbate and oxidised glutathione produced in the bundle sheath have to be transported to the mesophyll to be reduced, whereas foliar H2O2 was predominant in the mesophyll. Chilling damage in maize leaves is severe because of an inability to acclimate to low temperatures, even when the antioxidant capacity was altered by overexpression of Superoxide dismutase.