Drought enhances maize chilling tolerance. II. Photosynthetic traits and protective mechanisms against oxidative stress.

In the present research we studied the photosynthetic traits and protective mechanisms against oxidative stress in two maize (Zea mays L.) genotypes differing in chilling sensitivity (Z7, tolerant and Penjalinan, sensitive) subjected to 5 degrees C for 5 days, with or without pretreatment by drought. The drought pretreatment decreased the symptoms of chilling injury in Penjalinan plants estimated as necrotic leaf area and maximum quantum yield of photosystem II. Furthermore, drought pretreatment diminished the level of lipid peroxidation caused by chilling in Penjalinan plants. After one day of recovery from chilling the Z7 and drought-pretreated Penjalinan plants showed higher net photosynthesis rates than the non-drought-pretreated Penjalinan plants, thereby decreasing the probability of generating reactive oxygen species. The greater net photosynthesis was correlated with the greater NADP-malate dehydrogenase activity. No differences in either the de-epoxidation state of the xanthophyll cycle or the antioxidant enzyme activities were found among the chilled groups of plants. However, a drastic decrease in ascorbate content was observed in chilled Penjalinan plants without drought pretreatment. As we found an increase of H2O2 content after drought pretreatment, we suggest its involvement as a signal in the drought-enhanced chilling tolerance of maize.