UBC Theses and Dissertations
Impact of temperature regimes on flavonoid accumulation in Merlot (Vitis vinifera L.) grapes Yan, Yifan
Flavonoids are an important class of plant secondary metabolites, which impart color and mouthfeel to grapes and wine. Flavonoid accumulation is genetically and environmentally controlled in grapes. Among the environmental factors, temperature is arguably the one that most affects flavonoid accumulation in grape berry. High temperatures (e.g., 30-35 °C) were shown in previous reports to impair anthocyanin accumulation in red grape varieties. Most of the studies compared only two or three temperature regimes and have never investigated the effect of the difference between day and night temperatures on flavonoid accumulation. This study employed controlled-environment (growth chamber) experiments to investigate the effect of temperature regimes and the difference between day and night temperatures on flavonoid accumulation in grapes, with an emphasis on anthocyanins and flavonols. Five temperature regimes were imposed on potted Merlot grapevines during berry ripening in each experiment (day/night, °C: 20/10, 20/15, 25/15, 35/25, 35/30 in Experiment 1; 20/10, 20/15, 25/15, 25/20, 30/20 in Experiment 2). In both experiments, high temperature regimes (i.e., 30/20, 35/25, and 35/30) decreased anthocyanin and flavonol concentrations and increased the relative concentration of 3’4’5’-substituted and methoxylated anthocyanins and flavonols as well as acylated anthocyanins, with comparison to low temperature regimes (i.e., 20/10 and 20/15). The difference between day and night temperatures exerted minor effect when regimes with the same day and different night temperatures were compared. When grapevines were subjected to the same night temperature, a larger difference between day and night temperatures (ΔT = 10 °C, e.g., 25/15) reduced the anthocyanin and flavonol level, with comparison to a smaller temperature difference (ΔT = 5 °C, e.g., 20/15). Gene expression analyses revealed that VviF3’H and VviF3’5’Hs integrated for the regulation of 3’4’5’-substituted anthocyanin accumulation and Vvi3AT controlled the level of anthocyanin acylation; the down-regulation VviFLS4 and VviMybF1 expression in high temperature regimes led to the corresponding reduction of flavonol accumulation. These results indicate that modulation of anthocyanin and flavonol accumulation occurs partially at the transcriptional level. Finally, this study suggests that day temperature plays a more important role than night temperature in determining the concentration and composition of anthocyanins and flavonols in grape berry.
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