Objective To explore the effect of exogenous abscisic acid (ABA) on tobacco young seedlings under low temperature stress, and to provide a theoretical basis for the fundamental research and practical application of ABA in tobacco cold resistance physiology.

Method Tobacco seedlings 'Yujinxiang 1' with six leaves were used as the experimental material. Tobacco seedlings treated with water at room temperature served as the positive control (CK), while tobacco seedlings treated with water at 8 (±1) ℃ under low temperature stress served as the negative control (CK-0). A pot experiment was conducted to investigate the effects of different concentrations of ABA (10, 20, 30, 50 μmol/L) on various physiological indices of tobacco seedlings under low temperature stress, including photosynthetic pigment content, soluble protein content, soluble sugar content, MDA content, proline content, as well as POD and SOD activities. The physiological indices of tobacco seedlings treated with exogenous ABA were analyzed using principal component analysis and the membership function method.

Result Exogenous ABA at different concentrations had a dose-effect on the short-term cold stress of tobacco seedlings. With the increase of exogenous ABA concentration, the alleviating effect of exogenous ABA on the cold stress of tobacco seedlings as a whole showed a trend change from promoting to inhibiting, but low concentration of ABA could inhibit the increase of the content of osmoregulatory substances under cold stress. Based on the analysis of physiological and biochemical indicators combined with membership functions, exogenous application of 20 μmol/L ABA can maximize the alleviation of growth inhibition in tobacco seedlings under cold stress conditions. Specifically, after 72 hours of cold stress, the contents of photosynthetic pigments, chlorophyll a, soluble protein, soluble sugar, and the activities of POD and SOD in the leaves of tobacco seedlings treated with 20 μmol/L ABA were 33.54%, 36%, 12.62%, 33.34%, 40.87%, and 9.92% higher, respectively, compared to the control group (CK-0). Meanwhile, the contents of MDA and proline were 18.16% and 14.31% lower, respectively, compared to the CK-0 group. The treatment amount is less and the cost of prevention of cold injury can be saved.

Conclusion In production, 20 μmol/L ABA can be sprayed before low temperature weather such as "Late spring cold snap" to improve the tolerance of tobacco seedlings to low temperature stress, effectively prevent cold damage, and significantly reduce low temperature damage.