New evidence for the functional roles of volatile and non-volatile isoprenoids in stressed plants

Mediterranean plants are challenged against extreme, often unpredictable stress events which may pose severe constrains for the plant survival, as uncontrolled reactive oxygen species (ROS) generation ultimately lead to cell death. Secondary metabolites, which are highly responsive to environmental drivers, constitute a flexible system aimed at countering drastic perturbations in the cellular ROS homeostasis. Recent evidence supports the notion of isoprenoids (products of methylerythriol phosphate (MEP) pathway) as aimed at quenching ROS, not only devoted at avoiding ROS formation. Here we focus our attention on "essential isoprenoids" (i.e., carotenoids) and "non-essential isoprenoids" (e.g., isoprene), and how they constitute a well-coordinated system aimed at countering an excess of radiant energy to the chloroplast during stress progression. We also offer recent evidences of the functional roles of the end-product of MEP pathway, abscisic acid, as an essential regulator of the whole-plant metabolic machinery, and not merely of stomatal opening.