Responses of Drought Stress on Photosynthetic Trait and Osmotic Adjustment in Two Maize Cultivars

The responses of gas exchange, chlorophyll fluorescence parameters and osmotic adjustment were studied in two different maize hybrids Zhengdan 958 (drought resistance) and Shaandan 902 (drought sensitive) under three different drought stresses (mild drought, moderate drought, severe drought) and normal irrigation in a pot experiment. The results showed that drought stress caused disorder in photosynthesis, damage in the integrity of cellular membranes and increased the amounts of osmotic active substance (proline and soluble sugar) in both two cultivars. Thus these may have an important role in acclimation process to drought stress. However, compared with drought-stressed Shaandan 902, drought-stressed Zhengdan 958 showed higher values of maximum leaf net photosynthetic rate (Pn,max), apparent quantum efficiency (AQY), light saturation point (LSP), maximum rate of electron transport driving RuBP regeneration (Jmax), maximum rate of RuBP carboxylatuin (Vc,max), PSⅡ actual quantum yield (Φ PSⅡ) and photochemical quenching (qP); higher contents of soluble sugars and proline and lower content of MDA. These results indicate that Zhengdan 958 have a better self-protection of photosynthetic system, greater accumulation of substances for osmotic adjustment for eliminating the negative effects on cellular membranes may be the major physiological traits in the adapt ability to drought conditions.