**2. ROS role in plant growth and development**

Despite the continuous efforts and gains made in agriculture development during recent decades, many stress factors continue to harm the crop growth and productivity. Most of the crop plants thrive in suboptimal environmental surroundings. Stressful conditions are the main factor preventing them from exhibiting their maximum genetic competence in terms of growth and reproduction, and as a result, plant productivity suffers as an outcome of these aberrant circumstances [15–17]. These pressures resulted in significant productivity and economic declines around the world. These stresses might be either biotic or abiotic. Pathogens (viruses, bacteria, and fungi), insects, herbivores, and rodents are all examples of biotic stresses. On the other hands, drought (water scarcity situation), salinity (high concentration of salt), cold (chilling and frost), heat (high temperature), flooding (water excess), radiation (high-intensity ultraviolet and visible light), contaminants, and toxins (heavy metals, pesticides, and aerosols), and soil nutrient deprivation are all examples of abiotic stresses [16, 18]. Any of these conditions either separately or in combinations may have varying degrees of influence on plant growth and development (**Table 1**).

Environmental factors influence plant growth and development through morphological, physiological, biochemical, and molecular alterations. The plant organelle metabolic paths are vulnerable to variation in environmental factors [13]. Tolerance can be attained by plant breeding or cultural activities that mitigate damages and require knowledge of the plant's stress response and how it affects individual plants and plant processes [42]. Various mechanisms linked with abiotic stress instruct plant cells to develop oxygen radicals and their derivatives referred to as reactive oxygen species (ROS). Furthermore, the development of reactive oxygen species (ROS) is a




## *ROS Regulation Mechanism for Mitigation of Abiotic Stress in Plants DOI: http://dx.doi.org/10.5772/intechopen.99845*

#### **Table 1.**

*Effect of various abiotic stresses on plant growth, development and production.*

crucial mechanism in higher plants, since it is used to relay cellular signaling information in reaction to fluctuating environmental conditions.

As the crop yield is depending on the plant's capability to respond to various forms of environmental stresses, most of which causes oxidative stress and increases concentration of reactive oxygen species (ROS). Increased ROS accumulation is closely

related to increased environmental stress. A variety of biotic and abiotic factors can disrupt the balance between ROS production and the scavenging process, and responsible for raising their levels in intra-cellular [10]. All of these are accountable to cause serious oxidative injury to the plants, limiting their growth parameters and revenue ultimately (**Figure 1**).

Reactive oxygen species (ROS) also play a role in a variety of processes, including cell growth, production, and comeback to biotic and abiotic environmental inducements, as well as programmed cell death and signal transduction. Stressors, hormones, growth, and a variety of additional metabolic pathways can all arouse ROS formation, which can then trigger other pathways or serve as direct defense compounds in the plant body [43]. But, when ROS synthesis exceeds cellular scavenging potential, it disturbs the cellular redox homeostasis and produce ROS [44, 45]. To counter these stresses, plants have antioxidant pathways that scavenge excess ROS and avoid cell damage. Thus, plant synthesis and quenching are out of equilibrium, resulting in yield losses due to oxidative disruption. Though, it is difficult to identify this drop to oxidative damage due to the many processes involved in ROS synthesis; however, stresses and oxidative damage are interconnected and are liable for yield reduction [46].

Therefore, understanding the oxidative appliances in plants might be an aid in the growth of plants that are best suited to their surroundings. Plants stimulate antioxidant defense mechanisms in response to stress, which helps in the continuation of cell constituent's structural integrity and, potentially reduces oxidative injury. Plant defense is aided by several antioxidant enzymes. As a result, maintaining a high antioxidant ability to abolish toxic levels of ROS has been concurrent to improved crop plant capacity towards stress tolerance.

Manipulating ROS scavenging enzyme organizations is a likely method for producing transgenic plants that are more tolerant to a variety of stress situations; however, more research is needed for this since many enzymes and isoforms are

involved, and ROS is only one of the promising issues of plant tolerance to environmental and biotic stresses [47].

#### **2.1 Plant antioxidant defense system overview**

To minimize possible harm to cellular components, as well as to sustain growth, metabolism, development, and total yield, the balance between ROS generation and removal at the intracellular level must be closely controlled and/or competently processed. Antioxidants scavenge ROS and/or regulate ROS development, either directly or indirectly [48]. This antioxidant defence system comprises low-molecularweight non-enzymatic antioxidants and some antioxidant enzymes [49]. Nonenzymatic components include tocopherol, carotenoids, phenolic compounds, flavonoids, alkaloids, and non-protein amino acids, besides cellular redox buffers like ascorbate (AsA) and glutathione (GSH) [50–52].

Numerous antioxidant enzymes, like superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), peroxidase (POX), polyphenol oxidase (PPO), peroxiredoxins (PRXs), Thioredoxins (TRXs), and ascorbate-glutathione (AsAGSH) cycle enzymes, such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) are the parts of the enzymatic components of the antioxidant defense organization [53–56]. The above non-enzymatic antioxidants function in combination with antioxidant enzymes to keep the balance between ROS synthesis and detoxification [52, 54].

### **3. ROS involvement in plant stress responses**

The disruption of the equilibrium between the formation of reactive oxygen species (ROS) and antioxidant defense systems, resulting in an unsustainable accumulation of ROS and oxidative stress induction in the plant body, is one of the most imperative effects of environmental stresses. Both enzymatic and non-enzymatic antioxidant defense systems maintain the balance between reclamation and ROS generation when exposed to extreme environmental conditions [57]. Based on their concentration in plants, reactive oxygen species (ROS) can play both harmful and advantageous functions. ROS are unwelcome and dangerous byproducts of natural cellular metabolism at elevated amounts. But, serve as a second messenger in intracellular signaling flows that facilitate a variety of retorts in plant cells at low concentrations. It causes oxidative destruction to lipids, proteins, and DNA, resulting in changes in intrinsic membrane features such as fluidity, ion transfer, enzyme activity loss, protein crosslinking, protein synthesis inhibition, and DNA damage, all of which contribute to cell death. Thus, ROS disrupt biomolecules and cause genetically programmed cell death events at high concentrations. Higher plants have an extensive and very robust plant ROS setup, which is made up of antioxidant enzymes and antioxidant particles, that keeps ROS levels under control to avoid oxidative harm. Environmental factors like heat [58], cold [59], drought [60], Al toxicity [61], organic pollutants (OPs) [62], and pathogens [63, 64] have all been revealed to bring ROS production in plant cells.

On the other hand, changes in ROS levels over time and space are inferred as signals for a variety of biological events, including growth, development, resistance to abiotic stress factors, appropriate response towards pathogen, and cell death. The

molecular communication connected with ROS arbitrated signal transduction, which leads to gene expression management, is one of the essential early stress responses in the plant's acclamatory output. By altering the cell's redox equilibrium, ROS might function as a "second messenger," modifying the actions of particular proteins or gene expression. At any level of plant growth, the network of redox signals composes metabolism to regulate energy generation and consumption, interfering with primary signaling agents (hormones) to respond to evolving environmental nods. The consequence or fine-tuning of biological reactions to changed ROS levels is determined by interactions with other signaling molecules. Despite the recent identification of several constituents of the ROS signaling system, understanding how ROS-derived signals are incorporated to ultimately control biological processes like plant growth, development, stress adaptability as well as programmed cell death remains a challenge. To offset the negative impacts of oxidative stress, plants engage their antioxidant defense mechanism. Antioxidant defense ability, instead, vary according to plant species and genotype, stress kind, and period of exposure.
