Salicylic acid modulated flavonol biosynthesis in three key phases during grape berry development

Salicylic acid (SA) is a key signaling molecule involved in plant defense responses, former work indicated its regulating effects on some defense genes in plant materials, while the relationship between SA and flavonol biosynthesis during grape berry development remains obscure. By using the techniques of in vivo incubation of the grape berry (Vitis vinifera L. cv. Cabernet Sauvignon) tissues in SA-contained medium, the effects of exogenous SA on flavonol biosynthesis in three key phases (the rapid growth phase, the lag phase of growth and the veraison) of grape berry development were investigated in this work. The results showed that exogenous SA could modulate flavonol biosynthesis, but the modulation effects differed greatly in different phases of grape berry development. During the lag phase of growth and veraison, exogenous SA activated flavonol synthase (FLS) activities and induced the synthesis of new FLS protein. The activation of FLS activity could be blocked by protein synthesis inhibitor cycloheximide and mRNA transcription inhibitor actinomycin D during the lag phase of growth, but only actinomycin D inhibited exogenous SA at veraison. In accordance with the changes of FLS activities and amounts, total flavonol content was found to be modulated accordingly. But the contents of free flavonols had no correlations with SA in the rapid growth phase and veraison. The results suggested that exogenous SA could modulate flavonol biosynthesis of grape berries by activating FLS activity at specific developing phases, while the accumulation of flavonol compounds might be involved in the development of acquired resistance mediated by SA.