The Activity Changes of Anti-oxidation Protective Enzymes in Soybean Seedlings of Different Cultivars under Osmotic Stress and Its Stepwise Regression Analysis

Under 6% PEG treatment, the content of free proline and endogenous abscisic acid(ABA) in young leaves and roots of 6 drought-tolerant soybean cultivars increased up to the range of 274.9～441.2 μg/g DW and 18.66～28.83 μg/gDW, respectively. The content of free proline and ABA of 4 drought-sensitive cultivars was in the range of 145.6～258.9 μg/gDW and 8.7916.62 μg/gDW, respectively. Based on the above data, each of the drought-tolerant and sensitive cultivars was selected for further analysis. Under 4% PEG treatment, AsA-POD, CAT activities and TTC reduction changed with the treatment time (h), showing a tendency of 'to decline and increase alternately'twice. MDA content changed contrarily to the former tendency. SOD activities increased rapidly at first with POD and CAT activity. Stepwise regression equation of TTC reduction of different soybean cultivars showed that AsA-POD is the key enzyme in determining the ability of drought tolerance in soybean leaves.