Heat shock and UV-B episodes modulate olive leaves lipophilic and phenolic metabolite profiles

Abstract

Olea europaea L. is the basis of the olive oil chain value. Olive by-products remain economically underexplored despite their richness in polyphenols and fatty acids. Heat waves and raised UV-B radiation episodes (that increasingly affect Mediterranean orchards) may influence these compounds. Herein we characterize the most relevant leaf lipophilic and phenolic compounds of an important Portuguese cultivar Cobrançosa, immediately and 30 days after exposure to high UV-B radiation or heat shock (HS). Plants were exposed to either UV-B (12 kJ m−2 d-1) or HS (40 °C for 2 h) for two consecutive days. Hydroxycinnamic acids, triterpenes, sterols and fatty acids are less influenced by UV-B and HS, while the amounts of flavonoids, secoiridoids and monoterpenes increased. In particular, after both treatments, quercetin-3-O-glucoside levels increased in leaves, and UV-B stimulated oleuropein levels. HS reduced the amounts of verbascoside, oleuropein and luteolin-7-O-glucoside, while UV-B only decrease apigenin-7-O-rutinoside levels. Thirty days after UV-B and HS relief, these compounds showed different profiles. Whereas UV-B recovering plants showed increased amounts of thymol-β-d-glucopyranoside, in HS recovering plants, the increase was more relevant for oleuropein, chrysoeriol-7-O-glucoside and luteolin-7-O-glucoside. Data evidence that Cobrançosa leaves are particularly rich in luteolin-7-O-glucoside, oleuropein, and oleic and palmitic acids, and that their levels may be stimulated by climate-change related conditions, contributing to the economical valorisation of leaves.