Effects of Exogenous GA 3 on Wheat Cold Tolerance

Abstract

To clarify the underlying physiological mechanism o f gibberellic acid (GA) in cold tolerance, the effects of exogenous GA 3 on malondialdehyde (MDA), osmoregulation substances and endogenous hormones levels in the ti ller nodes of two wheat cultivars, namely, Dongnongdongmai 1 (a cold insensitive culti var) and Jimai 22 (a cold sensitive cultivar), were investigated at three periods of co ld winter (0, -10, -25°C). The results showed that low concentrations of GA 3 (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 GA 3 (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/G A only in Dongnongdongmai 1 and had no influence on those in Jimai 22. The re-green ing rate of Dongnongdongmai 1 decreased as the concentration of exogenous GA 3 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 corre lated with re-greening rate. In conclusion, low exogenous GA 3 level could decrease endogenous GA content and ele vate ABA/GA ratio and soluble protein content, which hel p to improve cold tolerance. However, high exogenous GA 3 level decreased the ABA content and ABA/GA ratio, resulting in lower soluble sugar and protein conten t and aggravated oxidative damage, and finally weakened cold tolerance. The endogenous GA metabolism and ABA/GA balance play central roles in exogenous GA 3 mediated cold tolerance. Keywords : Cold stress, Physiological mechanism, Phytohormon e, Tiller node, Winter wheat.