| Potassium,as an important element for fruit trees,can increase soluble sugar contents in apple fruits.Soluble sugars in apple fruit are not only basic substance for the synthesis of quality components and flavor compounds,but also sucrose in them is used as a signal transduction molecule to regulate the growth and development of plants.Sucrose non-fermenting-1-related protein kinase 1(Sn RK1)is a member of the sucrose non-fermenting-1-related protein kinase(SnRK)family.As a key factor in the process of sugar signal transduction,it can directly or indirectly regulate the process of carbon assimilation and is also regulated by carbon metabolites.Therefore,in this study,the potted six-year-old dwarf apple(Malus domestica Borkh.)/M26(Malus pumila Mill.)trees were selected as the experimental materials.The dynamic changes of sugar contents,enzymes activities in sugar metabolism,and SnRK1 activity in apple fruits were studied under different levels of potassium treatments[0%(CK)?1.0%?2.0%and 3.0%].And their correlations were also analyzed.The regulation of potassium on sucrose metabolism and its relationship with SnRK1 in fruit were preliminarily revealed.The results obtained in the paper are as follows:1.The data of qulity index were analyzed,and the results show that suitable potassium concentration can improve fruit quality.Different levels of potassium treatments can increase apple fruit weight and soluble solid content.In the four treatment groups,it was found that apple fruit weight and soluble solids content in the medium potassium treatment were higher than those under other levels conditions.Compared with the 2%-K treatment group,the 3%-K treatment group showed lower single fruit weight and soluble solids content,and higher titratable acid content.2.With apple fruit maturing,fructose and sucrose contents increase significantly.Potassium treatment can significantly promote accumulation of Fru,Suc and Sor,and the promoting effect of the 2%-K treatment group was the most obvious.The 2%-K treatment had the greatest effect on the Suc content,which can increase by 35%.The resu lts showed that the appropriate amount of potassium treatment can increase the content of Fru,Suc and Sor in mature fruits,among which the promotion effect of sucrose content is the most obvious.3.The activities of SPS,NINV and AINV in fruit were significantly higher in the2-%K treatment group than in the 0%-K treatment group at the later stage of fruit development.While the activity of SUSY is promoted to some extent,but the effect is not significant.4.With the growth and development of apple fruit,the SnRK1 activities in different treated fruits first increased and then decreased.At 84 days after blooming,SnRK1 activity of all treatment groups reached a maximum,and subsequently,the activity of SnRK1 began to decline.With the increase of potassium content in fruit,the activities of SnRK1 were inhibited by 3.49%,25.67%and 18.23%respectively when fruits matured.This suggests that low potassium concentration probably promote SnRK1 kinase activity in fruit,while higher concentrations of potassium may inhibit SnRK1 activity.5.Analysis of correlations among SnRK1 activity,expression of SnRK1 related genes,and the expression level of SUSY related genes in different fruit development stages under different potassium levels showed that SnRK1 may phosphorylate and inactivate SPS in apple fruit.There was no obvious correlation between SnRK1 activity and Md SUSYs expression.6.According to the results in our study,a hypothesized mechanism is suggested:K indirectly improved AINV and NINV activities in the frist half of the expansion period to accumulate Fru and Glu,and when the K~+concentration in the fruit was accumulated to a certain extent,it can inhibit the SnRK1 activities on transcriptional regulation to promote SPS activity,and then Suc accumulated rapidly.It is concluded that Sn RK1 may be worked as an intermediate factor,together with K~+,affecting the accumulation of soluble sugars in fruit during the enlargement period. |
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