Abscisic Acid Improves Chilling-Induced Oxidative Stress in Trichosanthes kirilowii Maxim Seedlings

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Trichosanthes kirilowii, an important economic plant in China, is sensitive to chilling. To investigate the effect of abscisic acid (ABA) treatment on the chilling tolerance of Trichosanthes kirilowii Maxim, different concentrations of ABA were sprayed on Trichosanthes kirilowii leaves and the resulting catalase (CAT) and superoxide dismutase (SOD) activities and the malondialdehyde (MDA) content in the leaves were determined. The results indicated that at 4 ºC, the CAT and SOD activities increased at first and then decreased with increasing ABA concentration. By contrast, the MDA content decreased at first and then increased. They both had an extreme value when sprayed with 5.0 or 7.5 mg L-1 ABA. A real-time polymerase chain reaction was performed to investigate the influence of exogenous ABA on the CAT gene expression of Trichosanthes kirilowii leaves. The results indicated that at 4 ºC, the CAT relative gene expression showed a high degree of positive correlation with the enzyme activities of CAT and SOD, and a negative correlation with MDA content. These results led to three conclusions. First, exogenous ABA exhibits significant effect on the chilling tolerance of Trichosanthes kirilowii. Second, exogenous ABA significantly increases the enzyme activities of CAT and SOD under cold environments. Finally, under cold environments and the effect of ABA, the relative gene expression of catalase 2 (CAT2) gene was found to play an important role in the enhancement of the chilling tolerance of Trichosanthes kirilowii leaves.