Changes in the anthocyanin pathway related to phenolic compounds and gene expression in skin and pulp of cv. 'Istrska belica' (Olea europaea L.) during ripening

Abstract

The purpose of research was to study in detail the dynamics of the anthocyanin pathway during the ripening of olives, comprising the relative gene expression of nine enzymes and the contents of twelve phenolic compounds. The analyses were conducted on cv. 'Istrska belica' at seven maturity stages, separately in the pulp and the skin. Most phenolic compounds showed a higher content in the skin than in the pulp. Results showed that the accumulation of dihidroquercetin and dihydromyricetin started at the latest maturity stages. The most abundant phenolics evaluated in the current study present in both tissues were cyanidin-3-O-rutinoside and delphinidin-3-O-glucoside, both presented at all maturity stages, even when colour was not yet visible in the skin or pulp. Gene expression of enzymes revealed tissue-specific regulation during ripening. Genes expressions for phenylalanine ammonia lyase, chalcone synthase, chalcone isomerase, flavonoid 3-hydroxylase and flavonoid 3′-hydroxylase showed higher levels in the skin than in the pulp, and an upregulation during ripening in both tissues. Anthocyanidin synthase was the only gene with the highest expression at the beginning of ripening, with extreme decrease between second and third maturity stage, which suggests that the enzyme is mainly synthesized at the beginning of ripening and that enzyme activation starts at latest maturity stages. Our research contributes to a better understanding of the dynamics of phenolic accumulation and the relative gene expression of enzymes involved in the anthocyanin pathway in reveals tissue-specific changes during olive fruit ripening. The previous results are also supported by physical changes, which are reflected in a statistical increase in fruit weight, a decrease in fruit firmness and also by changes in appearance observed during ripening. Understanding the accumulation of anthocyanins could, through further study, help to improve the quality of the fruit and therefore the quality of olive products.