Moderate salt spraying on grapevine canopy induces differential modulation of anthocyanin synthesis profiles during early and late stages of berry ripening in Cabernet Sauvignon

Anthocyanin accumulation in the skin of red/black grape berries is a crucial quality parameter that is known to be influenced by salt content. During two consecutive seasons, we applied a mild salinity NaCl solution (20 mmol L-1 and 60 mmol L-1) to the grapevine canopy in a commercial vineyard to investigate anthocyanin biosynthesis during berry ripening. The results showed a gradual reduction in the mass of mature berries as the concentration of NaCl increased. However, the contents of reducing sugars, total phenols, and tannins exhibited an inverse trend. Compared to the control group, the treatment with 60 mmol L-1 NaCl significantly hindered ABA synthesis in berries at veraison. This reduction was associated with lower levels of anthocyanin and sugar accumulation, which was determined by the downregulation of key genes involved in the related pathways during the early stages of berry ripening. Conversely, during the late stages of berry ripening, there was a notable increase in both anthocyanin and sugar accumulation with rising NaCl levels. This observation aligned with the upregulation of key genes involved in anthocyanin metabolism and sugar transport. However, unlike the early stages, the ABA content in berries did not correlate with anthocyanin synthesis during the late stages of ripening under salt stress. Therefore, we concluded that anthocyanin accumulation was regulated under NaCl stress during berry ripening and exhibited different accumulation profiles at different developmental stages. Additionally, we noticed that the proportion of dihydroxylated/trihydroxylated anthocyanins was increased in salt-stressed berries at harvest, while the proportion of acylated anthocyanins was notably decreased. In summary, the findings suggested that the alteration in anthocyanin accumulation varied across different developmental stages of berries under moderate salinity stress.