Reactive Oxygen Species in Plant Physiology: Regulatory Mechanisms, Developmental Roles, and Nanomaterial Interactions: A Comprehensive Review

Reactive oxygen species (ROS) are metabolic by-products in plants, comprising extremely reactive molecules like singlet oxygen, superoxide, and hydroxyl radicals. Although ROS can be harmful at elevated concentrations and detrimental at deficient levels, plants modulate their amounts via enzymatic and non-enzymatic defensive mechanisms. Respiratory burst oxidase homologs (RBOH) and superoxide dismutase (SOD) are essential for the synthesis and conversion of reactive oxygen species (ROS). Reactive oxygen species (ROS) are involved in various physiological processes, such as pollen formation, seed germination, fruit maturation, stomatal movement, and plant defense mechanisms. In pollen formation, reactive oxygen species (ROS) govern programmed cell death (PCD) in tapetal cells, facilitating appropriate microspore release. During seed germination, reactive oxygen species (ROS) regulate the equilibrium between abscisic acid (ABA) and gibberellins (GAs), affecting dormancy and germination responses. Furthermore, reactive oxygen species serve as beneficial stimuli during the initial phases of fruit growth but may induce oxidative stress in subsequent stages. Reactive oxygen species (ROS) also contribute to stomatal control, with abscisic acid (ABA)-induced ROS generation facilitating stomatal closure during drought stress. Moreover, reactive oxygen species (ROS) are crucial in plant defense by initiating signaling cascades that elicit immunological responses to microbial assaults. In recent years, nanomaterials (NMs) have become significant contributors to reactive oxygen species (ROS) modulation. ROS-inducing nanomaterials, including AgNPs and Cu-based nanoparticles, provoke oxidative stress responses that bolster plant resistance, whereas ROS-scavenging nanomaterials, such as CeO? and Mn?O? nanoparticles, alleviate oxidative damage and boost stress tolerance. Notwithstanding progress in comprehending ROS roles in plants, some pathways remain ambiguous, especially for pollen and fruit development, seed germination, and nanoparticle-mediated ROS modulation. This review consolidates existing knowledge on the roles of reactive oxygen species in plant physiology and emphasizes potential research avenues to clarify their regulation mechanisms.