ROS and RNS in plant physiology: an overview

Abstract

The production of reactive oxygen species (ROS) is the unavoidable consequence of aerobic life. ROS is a collective term that includes both oxygen radicals, like superoxide (O 2. -) and hydroxyl (·OH) radicals, and other non-radicals such as hydrogen peroxide (H2O2), singlet oxygen ((1)O2 or (1)Δg), etc. In plants, ROS are produced in different cell compartments and are oxidizing species, particularly hydroxyl radicals and singlet oxygen, that can produce serious damage in biological systems (oxidative stress). However, plant cells also have an array of antioxidants which, normally, can scavenge the excess oxidants produced and so avoid deleterious effects on the plant cell bio-molecules. The concept of 'oxidative stress' was re-evaluated in recent years and the term 'oxidative signalling' was created. This means that ROS production, apart from being a potentially harmful process, is also an important component of the signalling network that plants use for their development and for responding to environmental challenges. It is known that ROS play an important role regulating numerous biological processes such as growth, development, response to biotic and environmental stresses, and programmed cell death. The term reactive nitrogen species (RNS) includes radicals like nitric oxide (NO· ) and nitric dioxide (NO2.), as well as non-radicals such as nitrous acid (HNO2) and dinitrogen tetroxide (N2O4), among others. RNS are also produced in plants although the generating systems have still not been fully characterized. Nitric oxide (NO·) has an important function as a key signalling molecule in plant growth, development, and senescence, and RNS, like ROS, also play an important role as signalling molecules in the response to environmental (abiotic) stress. Similarly, NO· is a key mediator, in co-operation with ROS, in the defence response to pathogen attacks in plants. ROS and RNS have been demonstrated to have an increasingly important role in biology and medicine.

Free Radicals and Antioxidant System in Seed Biology

“…Cellular antioxidant mechanisms control ROS concentrations, rather than to eliminate them completely, suggesting that some ROS may act as signaling molecules [5,[34][35][36][37]46]. Although ROS have been considered as detrimental to seeds, advances in plant physiology evaluated them as messengers of various signal transduction pathways in plants.…”

“…Although ROS have been considered as detrimental to seeds, advances in plant physiology evaluated them as messengers of various signal transduction pathways in plants. ROS are suggested as being beneicial for seed germination, seedling growth, protection against pathogens and controlling the cell redox status [28][29][30][31][32][33][34][35][36][37][38][39][40]. H 2 O 2 is shown to be involved in the tolerance to various abiotic stresses acting as a secondary messenger [71], in cellular defense mechanisms against pathogens [72].…”

“…It is suggested that cellular membranes in germinating tissues are vulnerable to damage from desiccation [10,69]. After the loss of desiccation tolerance several products of peroxidized lipids are accumulated [45], and activated forms of oxygen are generated through xanthine oxidase [35,48,50]. Some studies have also suggested [37].…”

“…ROS are also proved to act as a positive signal in seed dormancy release [30][31][32][33]. The dual function of ROS in plants depends on the levels of antioxidant compounds, and enzyme activities release [34][35][36][37][38]. By this way, plants can eliminate potentially harmful ROS that is produced under stress conditions, or control ROS concentrations in order to regulate various signaling pathways [34][35][36][37][38].…”

Production Sites of Reactive Oxygen Species (ROS) in Organelles from Plant Cells

“…The main ROS mostly investigated are superoxide radical (O 2 , and hypochlorous acid (HClO) as non-radical. Under normal conditions, these molecules are produced in many metabolic pathways as normal by-product, being the respective electron transport chains present in chloroplasts and mitochondria the main sources of these ROS (Halliwell 2006;del Río 2015). However, the presence of free metals, such as iron, copper, and manganese, released from metalloprotein complexes can also contribute to ROS production.…”