Plant Phenolics: The Primary Roles of a Class of Secondary Compounds in Stress Adaptation.

Plants produce a wide array of compounds that help not only in its growth and survival, but also support the majority of the non-autotrophic life forms.  Though quantitatively and functionally less significant to primary metabolites, plant secondary metabolites (PSMs) are of prime importance in organismal, and plant-environmental interactions. Unlike primary metabolites, PSMs have the ability to mitigate the impact of both abiotic and biotic environments, and hence they influence the ability of plants to adapt to changing environments. Thus most of the PSMs have multiple complementary roles in plant-environmental and plant-organismal interactions that consequently enhance the overall plant fitness. This information is vital to gain a predictive understanding of how the plants would respond and adapt to changing environments, and how this adaptation will reflect in the nutritive quality of the crops.

Phenolic compounds in plants include monophenolics, and polyphenolics such as lignin, tannins, and flavonoids. We studied the changes in molecular-level composition of monomeric and polymeric phenolics in plants exposed to climatic stress under simulated warming (warmed and un-warmed) and precipitation (drought, ambient, wet) treatments using metabolomics approach.  Irrespective of the precipitation treatments, the composition of monophenolics generally increased with drought treatments through the upregulation of shikimate pathway, whereas the concentration of flavonoid compounds increased with warming treatments. Apart from their total content, the glycosylation pattern of flavonoids also changed with climatic treatments, with warming resulting in abundance of flavonoids glycosylated by deoxy sugars. Drought treatment lead to a greater production of tannins that were less polymerized, whereas tannins produced under wet conditions, though less in quantity, were highly polymerized. The potential of the above changes in the quantity and composition of phenolic profile for the mitigation of abiotic stress in plants will be discussed.