Response of organic acid metabolism in the young and ripening grape berries in vitro to ambient temperature

Organic acids, the important flavor compounds in grape berries, are altered by temperature during berry development. To mitigate potential interference encountered in field experiments, we employed in vitro culture techniques to investigate the impact of ambient temperature (AT) on organic acid metabolism at various developmental stages. The results showed that for the young berry (YB), organic acid accumulation rose gradually below 35 °C, but at 40 °C, tartaric and malic acid were significantly inhibited. In comparison to temperatures below 35 °C, ripening berry (RB) exhibited accelerated degradation of malic acid and an increase in tartaric acid content at 40℃. Notably, the enzymes activity of NADP-malate dehydrogenase (NADP-MDH) and NADP-isocitrate dehydrogenase (NADP-IDH) exhibited a significant increase, whereas there was a substantial decrease in NADP malic enzyme (NADP-ME) activity. AT altered the expression of organic acid metabolism genes, exhibiting distinct patterns between YB and RB. At 40 °C, most genes were suppressed; however, the levels of tartaric acid synthesis genes increased during the RB stage, consistent with the rise in tartaric acid content. The correlation analysis revealed that the transport of organic acids plays a pivotal role in the alteration of grape’s organic acid content induced by AT. Our study uncovered ambient temperature’s impact on grape organic acid metabolism via in vitro experiments, providing a guidance for organic acid biosynthesis regulation in grape berry.