Role of Stress and Defense in Plant Secondary Metabolites Production

Abstract

Secondary plant metabolites are natural bioactive compounds which are an important income for the pharmaceutical, food, cosmetic, agriculture, and other sectors due to their health-promoting properties and prevention and treatment of some diseases. The secondary metabolites can be classified into three main groups: phenolic compounds, terpenoids, and nitrogen compounds. The secondary metabolism in plants is a mechanism of adaptation and evolution as a defense to harsh environmental factors that induce stress. According to the hormesis curve of each plant model, the stress can be divided into distress (bad stress that leads to damage and ultimately plant death) or eustress (good stress that leads to activation of secondary metabolism). The environmental factors can be divided into biotic and abiotic which can be artificially induced to activate plant defense responses leading to the production of secondary metabolites. Several approaches to this process called elicitation have been proposed in the last decades with different types of metabolism-inducing factors or elicitors. Novel elicitation using abiotic factors includes electromagnetic waves (including several wavelengths of the light spectra, and electric and magnetic fields), acoustic waves, nanostructures, volatile compounds, nutrient deprivation, and several metals and salt soil pollutants. In the same order, novel elicitation using biotic factors include new bacteria consortium, fungi, phytohormones, and miRNA solutions. In general, the purpose of elicitation is to interact with the biochemical routes in order to produce secondary metabolites in high quantities, usually with negative effects in biomass production or morphology, but increasing plant quality in terms of aroma, taste or color. The metabolic profile and general response of elicitation vary greatly depending on the plant model, the elicitor level or concentration, and the stimulation time. Considering these facts, this chapter clearly and concisely discusses the most current strategies of elicitation for the increase of secondary metabolites production in plants.