Effect of exogenous abscisic acid on the cold resistance of Brassica rapacv.Longyou(winter rape) 8 cultivated at different foliar in northern China

The aim of this study was to determine the effects of exogenous abscisic acid(ABA)on the cold resistance of Brassica rapa(winter rape,cultivar Longyou 8)under low temperature stress.Leaves of Longyou8 were sprayed with 10mg/L ABA when the plants were at the three-,five-,six-,and seven-leaf stages before winter.Plants at the same stages were sprayed with distilled water as the control.The overwintering rate,yield and physiological and biochemical indexes of Longyou 8were determined after a cold treatment(-5℃).The plants sprayed with ABA showed significantly increased overwintering rates and yields,higher activities of antioxidant enzymes,and increased contents of physiological and biochemical substances that function as osmotic regulators.The effect was extremely significant after low temperature stress,when the overwintering rate and yield of ABA-treated plants were 14.3% and 8.0% higher than their respective values in the control plants.The activities of superoxide dismutase,peroxidase,and catalase were 39.8%,20.8%,31.0% higher,respectively,in ABA-treated plants than in control plants after the low temperature treatment.The contents of soluble protein,soluble saccharides,and free proline were 104.5%,120.1%,and 77.7% higher,respectively,in the ABA-treated plants than in control plants after the low temperature treatment.The best stage for ABA application was the six-leaf stage.Application of ABA also increased root activity and decreased the contents of malondialdehyde,a marker of lipid peroxidation.Together,these results show that spraying with ABA can improve the cold resistance of winter rape in northern China.