Changes of flavonol synthase and flavonol contents during grape berry development

Flavonols as an important kind of flavonoids not only have many defense-related functions, but also play an important role as potent antioxidants. Flavonol synthase (FLS) as the key enzyme in flavonol synthesis determines the final contents of flavonols in plant materials. The objective of this work was to study the changes of total flavonol content, free flavonol content, the individual flavonol aglycone contents and the two flavones (luteolin and apigenin) contents during grape berry development. The activity and the amount of the changes of FLS during grape berry development were also estimated. The results showed that quercetin, myricetin, kaempferol, isorhamnetin and galangin were detectable during grape berry development, and quercetin aglycone predominated in the total flavonol content in rapid growth phase, lag growth phase and the latter part of the ripening phase, myricetin aglycone witnessed a great increase at veraison, although kaempferol, isorhamnetin and galangin only accounted for a little part of the total flavonol contents but their individual contents all increased after veraison and kaempferol witnessed its highest content at the ripening phase. When it came to the contents of total phenols, total flavonoids, total flavonols and free flavonols, all of them showed accumulated peaks at both the rapid growth phase and the ripening phase. The result of FLS activity had a highly positive correlation with the total contents of flavonols, and the immunoblotting analysis detected two proteins whose signal intensities were in accordance with the FLS activities.