Effects of drought stress on phenolic accumulation in greenhouse-grown olive trees (Olea europaea)

The present study evaluates the effects of severe drought stress on the content of phenolic compounds in olive leaves, namely hydroxytyrosol, tyrosol, p-hydroxybenzoic acid, catechin, luteolin 7-O-rutinoside, luteolin 7-O-glucoside, apigenin 7-O-glucoside, quercetin, apigenin, pinoresinol, oleuropein and verbascoside in greenhouse-grown plantlets. The results showed that oleuropein, verbascoside, luteolin 7-O-glucoside and apigenin 7-O-glucoside were the most important phenolic compound of stressed olive plants and can represent up to 84% of the total amount of the identified phenolic compounds. Application of drought stress caused a significant increase in the level of oleuropein (87%), verbascoside (78%), luteolin 7-O-glucoside (72%) and apigenin 7-O-glucoside (85%), when compared to the control. The elevated values of these phenolic compounds can help controlling the water status of olive plants and avoiding serious oxidative damage induced by water deficit stress. To our knowledge, this is the first report to show the boost in the concentrations of verbascoside, luteolin 7-O-glucoside and apigenin 7-O-glucoside in the leaves of olive trees after water deficit stress.