The Combined Environmental Stress on the Leaves ofOlea europaeaL. and the Relief Mechanism Through Biosynthesis of Certain Secondary Metabolites

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 ofOlea europaeaL.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 ofl-Dopa decarboxylase-an enzyme common to plants and animals, bisconnected to this pathway-is rapidly increased in order to metabolize the highly toxicl-Dopa or the amino acidl-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.

Automated summary

Plants under stress in a Mediterranean climate produce secondary metabolites as a relief response, including an increase in reactive oxygen species accumulation and a decrease in absorbance of photosynthetic pigments. The activated secondary metabolic pathway also promotes the synthesis of antioxidant phenolic compounds.