Effects of Exogenous GA3 on Wheat Cold Tolerance

To clarify the underlying physiological mechanism of gibberellic acid (GA) in cold tolerance, the effects of exogenous GA3 on malondialdehyde (MDA), osmoregulation substances and endogenous hormones levels in the tiller nodes of two wheat cultivars, namely, Dongnongdongmai 1 (a cold insensitive cultivar) and Jimai 22 (a cold sensitive cultivar), were investigated at three periods of cold winter (0, -10, -25°C). The results showed that low concentrations of GA3 (0.1 and 1 µM) decreased the endogenous GA concentration in both cultivars, but only increased the abscisic acid (ABA)/GA ratio in Dongnongdongmai 1. High concentrations of GA3 (10 and 100 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 1 and had no influence on those in Jimai 22. The re-greening rate of Dongnongdongmai 1 decreased as the concentration of exogenous GA3 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 GA3 level could decrease endogenous GA content and elevate ABA/GA ratio and soluble protein content, which help to improve cold tolerance. However, high exogenous GA3 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 GA3 mediated cold tolerance.