[Relationships of wheat seed vigor with enzyme activities and gene expression related to seed germination under stress conditions.]

This study aimed to analyze the enzyme activities and gene expression differences related to seed germination in different wheat genotypes, and to clarify the relationship between seed vigor and the related enzyme activities as well as gene expression under stress germination conditions. We measured seed vigor, total soluble sugar content, soluble protein content, α-amylase activity, cysteine protease activity and gene expression of the related enzymes of four wheat cultivars under drought, artificial aging and cold soaking stress. Results showed that drought, artificial aging and cold soaking stress affected seed vigor to some extent. Under different germination conditions, total soluble sugar content showed an increasing trend with small amplitude at first and then decreased with small amplitude and after that increased rapidly again, while soluble protein content in the four cultivars gradually decreased with germination time. The α-amylase activity of the four cultivars showed a rising trend on the whole, but that of Yunong 949 and Lunxuan 061 declined after germinating for 60 hours after cold soaking stress. Cysteine protease activity decreased at first and then increased as a whole. However, under drought stress condition, cysteine protease activity of Yunong 949, Yumai 49-198 and Lunxuan 061 increased at first and then decreased and finally increased again. The α-AMY (α-amylase gene) expression levels increased at first and then decreased as a whole under different germination conditions. The expression level of α-AMY in Lunxuan 061 after cold soaking stress was higher than that of CK, while the α-AMY expression levels in four cultivars under other stress germination conditions were lower than that of CK. The expression level of CP (cysteine protease gene) showed an increasing trend. No significant difference of CP expression level was found in Chang 4738 between artificial aging treatment and CK. The CP expression levels in the four cultivars under other stress conditions were higher than that of CK. The results demonstrated that there was no direct relationship between the enzyme activities and gene expression levels of α-amylase and cysteine protease under different germination conditions. The α-amylase activity and total soluble sugar content had an extremely significant positive correlation, but the correlation between cysteine protease activity and soluble protein content was not significant. The α-amylase activity significantly positively correlated with vigor index under standard germination condition. However, the α-amylase activity had no significant correlation with vigor index under stress conditions. After cold soaking stress, cysteine protease activity significantly positively correlated with vi-gor index during seed germination, but the correlation was not significant under standard germination, drought stress and artificial aging.