Abstract
Plant secondary metabolites (PSMs) are vital for human health and constitute the skeletal framework of many pharmaceutical drugs. Indeed, more than 25% of the existing drugs belong to PSMs. One of the continuing challenges for drug discovery and pharmaceutical industries is gaining access to natural products, including medicinal plants. This bottleneck is heightened for endangered species prohibited for large sample collection, even if they show biological hits. While cultivating the pharmaceutically interesting plant species may be a solution, it is not always possible to grow the organism outside its natural habitat. Plants affected by abiotic stress present a potential alternative source for drug discovery. In order to overcome abiotic environmental stressors, plants may mount a defense response by producing a diversity of PSMs to avoid cells and tissue damage. Plants either synthesize new chemicals or increase the concentration (in most instances) of existing chemicals, including the prominent bioactive lead compounds morphine, camptothecin, catharanthine, epicatechin-3-gallate (EGCG), quercetin, resveratrol, and kaempferol. Most PSMs produced under various abiotic stress conditions are plant defense chemicals and are functionally anti-inflammatory and antioxidative. The major PSM groups are terpenoids, followed by alkaloids and phenolic compounds. We have searched the literature on plants affected by abiotic stress (primarily studied in the simulated growth conditions) and their PSMs (including pharmacological activities) from PubMed, Scopus, MEDLINE Ovid, Google Scholar, Databases, and journal websites. We used search keywords: “stress-affected plants,” “plant secondary metabolites, “abiotic stress,” “climatic influence,” “pharmacological activities,” “bioactive compounds,” “drug discovery,” and “medicinal plants” and retrieved published literature between 1973 to 2021. This review provides an overview of variation in bioactive phytochemical production in plants under various abiotic stress and their potential in the biodiscovery of therapeutic drugs. We excluded studies on the effects of biotic stress on PSMs.
Highlights
These Plant secondary metabolites (PSMs) variations can be due to genetic variability, but their concentrations are affected by environmental abiotic factors such as those expected to intensify with climate change [24], and herbivore and pathogen attacks [25,26]
In order to minimize the impact of various climate change-related stresses, plants produce diverse defense secondary metabolites, mainly phenolic and nitrogen-containing compounds
The biosynthesis of defense compounds in plants is often upregulated, and these compounds are associated with various pharmacological properties, suggesting that plants affected by climate change may be a rich resource for drug discovery
Summary
PSMs play essential secondary physiological and biochemical functions that ensure plant fitness and survival, concerning their interactions with the environment and coping with biotic and abiotic stress [1] These factors, especially abiotic stressors (nutrient deficiencies, seasons, salinity, wounding, drought, light, UV radiation, temperature, greenhouse gases, and climate changes), cause significant perturbations in chemotypes and levels of PSMs production. This scoping review examines recent advances related to PSMs in plants affected by abiotic stress/or abiotic growth factors, their roles as protective phytochemicals, and their potential for novel drug lead compounds Primary metabolites such as carbohydrates [13,14] and peptides [15,16] are known to play roles in the plant’s defense response, our review focuses on selected classes of PSMs, including flavonoids, terpenoids, alkaloids, saponins, tannins, and cyanogenic glycosides. We excluded studies on the effects of biotic stress on PSMs
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