X. Wang - College of Life Sciences, Northeast Agricultural University, Harbin ۱۵۰۰۳۰, Heilongjiang, People’s Republic of China.
Ch. Xu - College of Life Sciences, Northeast Agricultural University, Harbin ۱۵۰۰۳۰, Heilongjiang, People’s Republic of China.
J. Cang - College of Life Sciences, Northeast Agricultural University, Harbin ۱۵۰۰۳۰, Heilongjiang, People’s Republic of China.
Y. Zeng - Communication and Electronic Engineering Institute, Qiqihar ۱۶۱۰۰۶, People’s Republic of China.
J. Yu - College of Life Sciences, Northeast Agricultural University, Harbin ۱۵۰۰۳۰, Heilongjiang, People’s Republic of China.
L. Liu - College of Life Sciences, Northeast Agricultural University, Harbin ۱۵۰۰۳۰, Heilongjiang, People’s Republic of China.
D. Zhang - College of Life Sciences, Northeast Agricultural University, Harbin ۱۵۰۰۳۰, Heilongjiang, People’s Republic of China.
J. Wang - College of Life Sciences, Northeast Agricultural University, Harbin ۱۵۰۰۳۰, Heilongjiang, People’s Republic of China.

To clarify the underlying physiological mechanism of gibberellic acid (GA) in cold tolerance, the effects of exogenous GA۳ on malondialdehyde (MDA), osmoregulation substances and endogenous hormones levels in the tiller nodes of two wheat cultivars, namely, Dongnongdongmai ۱ (a cold insensitive cultivar) and Jimai ۲۲ (a cold sensitive cultivar), were investigated at three periods of cold winter (۰, -۱۰, -۲۵°C). The results showed that low concentrations of GA۳ (۰.۱ and ۱ µM) decreased the endogenous GA concentration in both cultivars, but only increased the abscisic acid (ABA)/GA ratio in Dongnongdongmai ۱. High concentrations of GA۳ (۱۰ and ۱۰۰ µM) increased the MDA level, retarded the accumulation of soluble protein and sugar in both cultivars, but decreased the content of ABA and the ratio of ABA/GA only in Dongnongdongmai ۱ and had no influence on those in Jimai ۲۲. The re-greening rate of Dongnongdongmai ۱ decreased as the concentration of exogenous GA۳ increased. Correlation analyses showed that MDA was negatively correlated with re-greening rate, while soluble protein, sugar ABA content, and ABA/GA ratio were positively correlated with re-greening rate. In conclusion, low exogenous GA۳ level could decrease endogenous GA content and elevate ABA/GA ratio and soluble protein content, which help to improve cold tolerance. However, high exogenous GA۳ level decreased the ABA content and ABA/GA ratio, resulting in lower soluble sugar and protein content and aggravated oxidative damage, and finally weakened cold tolerance. The endogenous GA metabolism and ABA/GA balance play central roles in exogenous GA۳ mediated cold tolerance.

Cold stress, Physiological mechanism, Phytohormone, Tiller node, Winter wheat