Spermidine promotes starch degradation to relieve the inhibitory effect of chilling on wheat seed germination

How the inhibitory effect of chilling on seed germination can be released is an important question in wheat production. In the present study, two wheat cultivars exhibiting differences in seed germination under chilling resistance were used, and their seeds were subjected to presoaking with spermidine and putrescine. The variations of polyamines and hormones and the carbohydrate in the seeds were measured under chilling stress. The objective of the present study was to investigate the effect of polyamines on wheat seed germination under chilling stress. The results indicated that spermidine could relieve the inhibitory effect of chilling stress on the seed germination of wheat, while putrescine had the opposite effect. Additionally, this specially effect of polyamines on the seed germination of wheat under chilling was related to abscisic acid and gibberellin. Spermidine significantly increased gibberellin levels in seeds and thereby promoted starch degradation in seeds. Additionally, the promotion effect of spermidine on the seed germination under chilling might be related to the increasing of abscisic acid concentration in seeds. However, external application of putrescine led to the excessively abscisic acid concentration in the wheat seeds and may by this reduced chilling resistance in seed germination stage of wheat. Taken together, these results indicated a continuous route of putrescine to spermidine synthesis that promotes chilling resistance in wheat seed germination and polyamine production, through the regulation of abscisic acid and gibberellin contents and starch degradation, to regulate wheat seed germination under chilling stress.