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.
