Reactive Oxygen Species, Antioxidant Responses and Implications from a Microbial Modulation Perspective

Abstract

Plants are exposed to various environmental stresses in their lifespan that threaten their survival. Reactive oxygen species (ROS), the byproducts of aerobic metabolism, are essential signalling molecules in regulating multiple plant developmental processes as well as in reinforcing plant tolerance to biotic and abiotic stimuli. However, intensified environmental challenges such as salinity, drought, UV irradiation, and heavy metals usually interfere with natural ROS metabolism and homeostasis, thus aggravating ROS generation excessively and ultimately resulting in oxidative stress. Cellular damage is confined to the degradation of biomolecular structures, including carbohydrates, proteins, lipids, pigments, and DNA. The nature of the double-edged function of ROS as a secondary messenger or harmful oxidant has been attributed to the degree of existing balance between cellular ROS production and ROS removal machinery. The activities of enzyme-based antioxidants, catalase (CAT, EC 1.11.1.6), monodehydroascorbate reductase (MDHAR, E.C.1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and guaiacol peroxidase (GPX, EC 1.11.1.7); and non-enzyme based antioxidant molecules, ascorbate (AA), glutathione (GSH), carotenoids, α-tocopherol, prolines, flavonoids, and phenolics, are indeed parts of the defensive strategies developed by plants to scavenge excess ROS and to maintain cellular redox homeostasis during oxidative stress. This review briefly summarises current knowledge on enzymatic and non-enzymatic antioxidant machinery in plants. Moreover, additional information about the beneficial impact of the microbiome on countering abiotic/biotic stresses in association with roots and plant tissues has also been provided.

Plants’ Physio-Biochemical and Phyto-Hormonal Responses to Alleviate the Adverse Effects of Drought Stress: A Comprehensive Review

“…Methods of chlorophyll fluorescence revealed a hazard and suggested that manufacturing operations were not balanced [82,83]. Drought stress causes plants to be adapted accordingly by regulating their stomata movement, adjusting their osmotic balance, and mounting an antioxidatant defense [8,84]. However, a protracted period of high-intensity limited water conditions might slow plant development, alter the morphological structure and biomass distribution pattern in tomato crops (Solanum lycopersicum L.), or cause mortality [15,85].…”

“…Carotenes are classified into two types: hydro-carbon carotenes [83], which include lycopene and xanthophylls, and carotene, which differs from the former due to the inclusion of lutein. The enzymatic antioxidant system contains carotenes, tocopherol, ascorbate, and enzymes such as APX, POD, SOD, polyphenol oxidase, glutathione reductase (GR), and CAT was, protecting carotenoids from the damaging of ROS [8,88,[94][95][96][97]. The enzymatic antioxidant system, which contains carotenoids, also protects carotenoids from ROS.…”

“…The rainfed genotypes exhibited a greater proline concentration than irrigated or humid genotypes. Agricultural plants undergo various internal physiological processes [8,68].…”

“…Photosynthesis, growth, and other critical physiological and biochemical activities are interrupted under drought stress conditions [6,7]. Previous studies [8][9][10] found that drought stress causes oxidative stress, damaging biological membranes and macromolecules (DNA, proteins, lipids, and photosynthetic pigments). Plants engage their natural defense systems in response to oxidative stress and create osmolytes [11], such as soluble proteins, proline, soluble sugars, and glycine betaine [12].…”

Role of Promising Secondary Metabolites to Confer Resistance Against Environmental Stresses in Crop Plants: Current Scenario and Future Perspectives

“…Tocopherols capacity to scavenge or quench lipid peroxides, oxygen radicals, or singlet oxygen, resulting in ROS detoxification, is the most significant role of tocopherols in alleviating abiotic stress-induced damage. Mutant and transgenic techniques that result in the loss or increase of function of tocopherol pathway genes likely to shed light on the compound’s role in plants ( Waqas et al, 2019 ; Zandi and Schnug, 2022 ). ROS are produced in response to various abiotic stimuli including dryness, salt, low temperature, and heavy metals, which harm membrane-containing organelles.…”