Effect of exogenous ABA on the cold resistance of branches of 21st Century and Jiushuo peaches

Abstract: 【Objective】This experiment was conducted to explore the effect of exogenous ABA treatments on peaches under low temperature stress in Qinhuangdao City, Hebei Province, China, in order to screen the optimal concentration for improving cold resistance.【Methods】In this study, annual branches of 21st Century and Jiushuo treated with different concentrations of ABA (0, 25, 50, 75 and 100 mg·L^-1 ) were used as test materials for evaluation of cold resistance under different artificial low temperatures (0, -5, -10, -15, -20, -25, and -30 ℃). Relative electrical conductivity (REC) was determined with the method of Li Hesheng. MDA was determined with Thiobarbituric acid method using the kit was provided by Shanghai Enzyme Link Biotechnology Co. Ltd.; soluble protein content was determined with a BCA protein method kit (Shanghai Enzyme Link Biotechnology Co. Ltd.); and soluble sugar content was determined with plant soluble sugar kit (Shanghai Enzyme Link Biotechnology Co. Ltd.). The endogenous hormones of ABA, GA, IAA and CTK were determined using ELISA method with kits pro-vided by Shanghai Enzyme Biotechnology Co. Ltd.. The differences in relative conductivity, MDA, soluble protein, soluble sugar and endogenous hormones (ABA, GA, IAA, CTK and ABA/GA) were investigated.【Results】The results showed that under low temperature stresses, the soluble protein and soluble sugar contents in 21st Century and Jiushuo branches treated with exogenous ABA increased compared with the control. 50 mg·L^-1 ABA treatment had the highest increase compared with the control. MDA and relative conductivity increased slowly compared with the control. The contents of ABA, GA, IAA, CTK and ABA/GA ratio increased first and then decreased. The endogenous ABA content in 21st Century at 0 ℃ was the highest in the 75 mg·L^-1 treatment and increased by 6.9% compared with the control; at -15 ℃, the highest ABA content was found in the 25 mg·L^-1 treatment, which increased by 2.1% compared with the control; at -30 ℃, the highest ABA content was found in the 25 mg·L^-1 treatment, which increased by 2.6% compared with the control. The ABA content in Jiushuo was the lowest in the 100 mg·L^-1 treatment at 0 ℃, which was 5% lower than the control; the lowest ABA was found in the 50 mg·L^-1 treatment at -15 ℃ and at -30 ℃, which was 9.1% and 7.4% lower than the control, respectively. The GA content in 21st Century was the lowest in 50 mg·L^-1  treatment at 0 ℃, which was 3.8% lower than the control; the lowest GA content was found in 50 mg·L^-1 treatment at -15 ℃, which was 3.2% lower than the control; GA content in 75 mg·L^-1 treatment at -30 ℃ increased slightly and was 1.5% higher than in the control. The GA content in Jiushuo was the lowest in 75 mg·L^-1 treatment at 0 ℃, which was 6.5% lower than the control at -15 ℃; the lowest GA content was found in 25 mg·L^-1 treatment, which was 0.1% lower than the control at -30 ℃; the GA content in 25 mg · L- 1 and 100 mg · L- 1 treatments was increased slightly and was 0.7% higher than the control. The endogenous IAA content in 21st Century was the lowest in 25 mg·L-1 treatment at 0 ℃, about 2.9% lower than the control. At -15 ℃, the lowest IAA content was found in 100 mg·L-1 treatment, which was 4.2% lower than the control. At -30 ℃, the IAA content of the sample treated with 50 mg ·L-1 ABA is less than 1% higher than the control. IAA content in Jiushuo was the lowest in 50 mg · L- 1 treatment at 0 ℃ , which was 4.8% lower than the control; at -15 ℃, the lowest IAA content was in 75 mg·L-1 treatment, which was 3.7% lower than the control; and at -30 ℃ the lowest IAA was found in 100 mg·L^-1 treatment at, which was 1.5% higher than the control. In 21st Century, endogenous CTK content at 0 ℃ was found in the 100 mg·L^-1  treatment, which increased 0.4% compared to the control; at -15 ℃, the lowest CTK content was found in the 100 mg·L^-1 treatment, which increased 2.2% compared to the control; at -30 ℃, the lowest CTK content was found in the 100 mg·L^-1 treatment, which decreased by 9.3% compared with the control. The endogenous CTK content of Jiushuo was the lowest in the 50 mg·L^-1 treatment at 0 ℃, with an increase of 2.5% compared with the control; at -15 ℃, the lowest CTK was found in the 50 mg·L^-1 treatment, with a decrease of 1.8% compared with the control; and the lowest CTK was in the 100 mg·L^-1 treatment at -30 ℃, with a decrease of 7.9% compared with the control. In 21st Century, ABA/GA ratio at 0 ℃. 50 mg·L-1 treatment had the highest ABA/GA ratio, which 8.1% hgiher compared with the control; At -15 ℃, the ABA/GA ratio of 50 mg · L- 1 treatment was the highest, increasing by 4.7% compared to the control; At -30 ℃, the ABA/GA ratio of 75 mg·L^-1 treatment was the highest among all treatment groups, but it was 0.5% lower than the control group. The ABA/GA ratio of Jiushuo was the highest in the 75 mg·L^-1 treatment at 0 ℃, with 4% increase over the control; the highest ABA/GA ratio was found in the 25 mg·L^-1 treatment at -15 ℃; and the highest ABA/GA ratio was in the 25 mg·L^-1 treatment at -30 ℃. At -30 ℃, the highest ABA/GA ratio was observed in the 25 mg·L^-1 treatment, with an increase of 1.8% compared with the control. The cold resistance indexes under low temperature stress were comprehensively evaluated by the affiliation function method, and the order ofcold resistance among ABA treatments for 21st Century was 50 mg·L^-1 ＞75 mg·L^-1 ＞100 mg·L^-1 ＞ 25 mg·L^-1 ＞0 mg·L^-1 (control); for Jiushuo, the order was 50 mg·L^-1 ＞25 mg·L^-1 ＞75 mg·L^-1 ＞100 mg·L^-1 ＞ 0 mg·L^-1 (control).【Conclusion】ABA treatment could affect the cold resistance of 21st Century and Jiushuo to different degrees. Based on the changes in physiological indexes, 50 mg·L-1 ABA treatment is the best, as it effectively alleviated frost damage and improve cold resistance.