The Combined Environmental Stress on the Leaves of Olea europaea L. and the Relief Mechanism Through Biosynthesis of Certain Secondary Metabolites

Abstract

Biosynthesis of certain secondary metabolites, as a relief response to the severe environmental stress of the mediterranean summer, is a major reaction of the plants thriving in areas with mediterranean-type climate. Some of these compounds are of great importance to both humans and the environment. Tracing of certain secondary metabolites, after the exposure of Olea europaea L. individuals to stressing environmental conditions, is the aim of this investigation. Our two-day cycle, detailed data indicate that soon after the summer mid-day severe environmental stress, a threefold increase (+ 256%) in reactive oxygen species accumulation is recorded in the leaves while the absorbance of the photosynthetic pigments is drastically reduced (up to − 60%). Then, the secondary metabolic pathway of the shikimic acid is activated and the expression level of l-Dopa decarboxylase—an enzyme common to plants and animals, bisconnected to this pathway—is rapidly increased in order to metabolize the highly toxic l-Dopa or the amino acid l-tyrosine, to dopamine or tyramine, respectively. These reactions promote, at a certain period of the 24-h cycle, the biosynthesis of oleuropein (41% increase), an antioxidant phenolic compound possessing a wide range of important pharmacological properties. By the evening twilight, when the environmental conditions turn to mild, the cell functions reset to normal.