Reactive oxygen species, antioxidants and signaling in plants

Several reactive oxygen species (ROS) are continuously produced in plants as byproducts of many metabolic reactions, such as photosynthesis, photo respiration and respiration, Depending on the nature of the ROS species, some are highly toxic and rapidly detoxified by various cellular enzymatic and nonenzymatic mechanisms. Oxidative stress occurs when there is a serious imbalance between the production of ROS and antioxidative defence. ROS participate in signal transduction, but also modify cellular components and cause damage. ROS is highly reactive molecules and can oxidize all types of cellular components. Various enzymes involved in ROS-scavenging have been manipulated and over expressed or down regulated. An overview of the literature is presented in terms of primary antioxidant free radical scavenging and redox signaling in plant cells. Special attention is given to ROS and ROS-anioxidant interaction as a metabolic interface for different types of signals derived from metabolisms and from the changing environment.     

Reactive oxygen species and antioxidants in legume nodules

Reactive oxygen species are a ubiquitous danger for aerobic organisms. This risk is especially elevated in legume root nodules due to the strongly reducing conditions, the high rates of respiration, the tendency of leghemoglobin to autoxidize, the abundance of nonprotein Fe and the presence of several redox proteins that leak electrons to O₂. Consequently, nodules are particularly rich in both quantity and diversity of antioxidant defenses. These include enzymes such as superoxide dismutase (EC 1.15.1.1) and ascorbate peroxidase (EC 1.11.1.11) and metabolites such as ascorbate and thiol tripeptides. Nodule antioxidants have been the subject of intensive molecular, biochemical and functional studies that are reviewed here. The emerging theme is that antioxidants are especially critical for the protection and optimal functioning of N₂ fixation. We hypothesize that this protection occurs at least at two levels: the O₂ diffusion barrier in the nodule parenchyma (inner cortex) and the infected cells in the central zone.     

Reactive oxygen species and antioxidants: Relationships in green cells

The imposition of oxidative stress leads to increased production of reactive oxygen species (ROS) in plant cells. Orchestrated defense processes ensue that have much in common between stresses, yet are also particular to the site of action of the stress and its concentration. Possible functional roles of these responses include, but are not restricted to, the protection of the photosynthetic machinery, the preservation of membrane integrity and the protection of DNA and proteins. Superimposed upon our understanding of cellular mechanisms for protection against abiotic stress is a newly discovered role of ROS in signalling and defense response to pathogens (J. L. Dangl, R. A. Dietrich and M. S. Richberg. 1996. Plant Cell 8: 1793–1807). Evidence to date suggests a coordinated response to ROS among different members of the superoxide dismutase (SOD) gene families. A further layer of complexity is afforded by reports of coordination of expression between ascorbate peroxidase and SOD genes. Our understanding of the signalling mechanisms that underlie these coordinated events is in its infancy. An exciting future lies ahead in which the orchestration of successful antioxidant stress responses will be gradually revealed. Current data suggest that complex regulatory mechanisms function at both the gene and protein level to coordinate antioxidant responses and that a critical role is played by organellar localization and inter-compartment coordination.     

Reactive oxygen species, water, photons and life.

Unique properties of oxygen and of the reactions with reactive oxygen species (ROS) participation are considered, the multiple ways of ROS generation and utilization are discussed in view of evidence for the absolute necessity of ROS for the normal vital activity. Many difficulties in the realization of the real role of ROS in vital activity are caused by the attitude to them only as to chemical substances, while they should be considered in the first place as the major participants of continuous flows of highly non-linear processes in which electron excited species emerge. These processes play a significant role in energy and informational flows in all the living systems. We suggest that the mechanisms of biological action of ROS are determined by the structural patterns (frequency-amplitude patterns of electron excited states generation and their relaxation) of the processes with ROS participation taking place in the aqueous environs. Energy released in such reactions is used as an activation energy for specific biochemical processes, for the continuous "pumping" of the non-equilibrium state of inter- and intracellular structural components, while the structural patterns of ROS reactions determine biochemical and physiological rhythmic modes. Special role of water in all these phenomena is discussed. From a broader perspective the processes with ROS participation emerging in water proceeded and were the necessary condition for origination and evolution of organic living forms on Earth.     

Reactive oxygen species induced smooth muscle responses in the intestine, vessels and airways and the effect of antioxidants

Numerous experimental data confirm the importance of reactive oxygen species (ROS) in physiological activities of smooth muscles and in the pathogenesis of various diseases with altered function of smooth muscles. The present study shows that smooth muscles of the intestine, airways and vessels, as well as their epithelium, endothelium and innervations, might be important targets of the ROS action. We demonstrated differences among the actions of various ROS (endogenous, exogenous, produced enzymatically, non-enzymatically) as well as among their actions in different smooth muscle tissues. Our results indicate that ROS are involved in changes in muscle tone, membrane conductance, calcium homeostasis, calcium-dependent processes, as well as in eicosanoid and nitric oxide metabolism. The effects of antioxidative enzymes (superoxide dismutase, catalase), of several drugs of natural origin (e.g. Kampo Medicines) and synthetic agents (e.g. stobadine, nitrosopine, ACE inhibitors) suggest that smooth muscle tissues are useful models to study ROS action and drug intervention in ROS induced injuries.     

细胞内活性氧与肿瘤

活性氧是细胞癌变过程中的重要角色：它本身能使DNA损伤,同时又促使致癌物质的产生并且许多致癌因子都是先诱导产生活性氧,然后通过活性氧起致癌作用的,但是另一方面,活性氧却有杀伤癌细胞和诱导细胞凋亡的能力许多抗癌药正是利用活性氧这一特点起作用的。     

Reactive oxygen species, mitochondria, apoptosis and aging

In this paper, we shall review various antioxygen defense systems of the cell paying particular attention to those that prevent superoxide formation rather than scavenge already formed superoxide and its products. The role of uncoupled, decoupled and non-coupled respiration, mitochondrial pore, mitochondrion-linked apoptosis will be considered. Mitochondrial theory of aging will be regarded in context of reactive oxygen species-induced damage of mitochondrial DNA. (Mol Cell Biochem 174: 305–319, 1997)     

Reactive oxygen and nitrogen species during meiotic resumption from diplotene arrest in mammalian oocytes

Mammalian ovary is metabolically active organ and generates by‐products such as reactive oxygen species (ROS) and reactive nitrogen species (RNS) on an extraordinary scale. Both follicular somatic cells as well as oocyte generate ROS and RNS synchronously and their effects are neutralized by intricate array of antioxidants. ROS such as hydrogen peroxide (H₂O₂) and RNS such as nitric oxide (NO) act as signaling molecules and modulate various aspects of oocyte physiology including meiotic cell cycle arrest and resumption. Generation of intraoocyte H₂O₂ can induce meiotic resumption from diplotene arrest probably by the activation of adenosine monophosphate (AMP)‐activated protein kinase A (PRKA)—or Ca²⁺‐mediated pathway. However, reduced intraoocyte NO level may inactivate guanylyl cyclase‐mediated pathway that results in the reduced production of cyclic 3′,5′‐guanosine monophosphate (cGMP). The reduced level of cGMP results in the activation of cyclic 3′,5′‐adenosine monophosphate (cAMP)‐phosphodiesterase 3A (PDE3A), which hydrolyses cAMP. The reduced intraoocyte cAMP results in the activation of maturation promoting factor (MPF) that finally induces meiotic resumption. Thus, a transient increase of intraoocyte H₂O₂ level and decrease of NO level may signal meiotic resumption from diplotene arrest in mammalian oocytes. J. Cell. Biochem. 111: 521–528, 2010. © 2010 Wiley‐Liss, Inc.     

Reactive oxygen species and seed germination

Reactive oxygen species (ROS) are continuously produced by the metabolically active cells of seeds, and apparently play important roles in biological processes such as germination and dormancy. Germination and ROS accumulation appear to be linked, and seed germination success may be closely associated with internal ROS contents and the activities of ROS-scavenging systems. Although ROS were long considered hazardous molecules, their functions as cell signaling compounds are now well established and widely studied in plants. In seeds, ROS have important roles in endosperm weakening, the mobilization of seed reserves, protection against pathogens, and programmed cell death. ROS may also function as messengers or transmitters of environmental cues during seed germination. Little is currently known, however, about ROS biochemistry or their functions or the signaling pathways during these processes, which are to be considered in the present review.     

Reactive oxygen species and sperm cells

There is a dynamic interplay between pro- and anti-oxidant substances in human ejaculate. Excessive reactive oxygen species (ROS) generation can overwhelm protective mechanism and initiate changes in lipid and/or protein layers of sperm plasma membranes. Additionally, changes in DNA can be induced. The essential steps of lipid peroxidation have been listed as well as antioxidant substances of semen. A variety of detection techniques of lipid peroxidation have been summarized together with the lipid components of sperm membranes that can be subjected to stress. It is unsolved, a threshold for ROS levels that may induce functional sperm ability or may lead to male infertility.     

Reactive oxygen species and yeast apoptosis

Apoptosis is associated in many cases with the generation of reactive oxygen species (ROS) in cells across a wide range of organisms including lower eukaryotes such as the yeast Saccharomyces cerevisiae. Currently there are many unresolved questions concerning the relationship between apoptosis and the generation of ROS. These include which ROS are involved in apoptosis, what mechanisms and targets are important and whether apoptosis is triggered by ROS damage or ROS are generated as a consequence or part of the cellular disruption that occurs during cell death. Here we review the nature of the ROS involved, the damage they cause to cells, summarise the responses of S. cerevisiae to ROS and discuss those aspects in which ROS affect cell integrity that may be relevant to the apoptotic process.     

Reactive oxygen species and tumor metastasis

The migration and invasion of cancer cells are the first steps in metastasis. Through a series of cellular responses, including cytoskeletal reorganization and degradation of the extracellular matrix, cancer cells are able to separate from the primary tumor and metastasize to distant locations in the body. In cancer cells, reactive oxygen species (ROS) play important roles in the migration and invasion of cells. Stimulation of cell surface receptors with growth factors and integrin assembly generates ROS, which relay signals from the cell surface to important signaling proteins. ROS then act within cells to promote migration and invasion. In this review, we collect recent evidence pointing towards the involvement of ROS in tumor metastasis and discuss the roles of ROS at different stages during the process of cancer cell migration, invasion and epithelial-mesenchymal transition.     

Reactive oxygen species and mitochondrial diseases

A variety of diseases have been associated with excessive reactive oxygen species (ROS), which are produced mostly in the mitochondria as byproducts of normal cell respiration. The interrelationship between ROS and mitochondria suggests shared pathogenic mechanisms in mitochondrial and ROS-related diseases. Defects in oxidative phosphorylation can increase ROS production, whereas ROS-mediated damage to biomolecules can have direct effects on the components of the electron transport system. Here, we review the molecular mechanisms of ROS production and damage, as well as the existing evidence of mitochondrial ROS involvement in human diseases.     

Reactive oxygen species and oxidative stress

Oxidative stress is defined as an imbalance between the production of reactive oxygen species (ROS) and the antioxidant capacity of the cell. For long, ROS have been considered as harmful by-products of the normal aerobic metabolism process of the mitochondria, implicated in a large variety of diseases. But there are now growing evidences that controlled ROS production also play physiological roles especially in regulating cell redox homeostasis and cell signaling. Biological ROS effects are now well documented. Data show that living organisms have not only adapted themselves to coexist with free radicals but have also developed mechanisms to use them advantageously. However their main sources and mechanisms of action remain poorly described. This review focuses on the main properties of ROS and their paradoxical effects.     

Reactive oxygen species and airway inflammation

Reactive oxygen species may be generated by several inflammatory cells which participate in airway inflammation and their production may be increased in asthma. Oxygen metabolites may contribute to the epithelial damage which is characteristic of asthmatic airways and may activate cells such as mast cells in the airway mucosa. Reactive oxygen species may cause bronchoconstriction, mucus secretion, have effects on airway vasculature, and may increase airway responsiveness. The role of reactive oxygen species in airway disease has been largely neglected, but appears to be an important area for future study. It is also possible that antioxidant defenses may be defective in asthma. If reactive oxygen species participate in the inflammatory response in airway disease, then radical scavengers or antioxidants could play a useful role in therapy.     

Reactive oxygen species and plant immunity

Reactive oxygen species (ROS) play a key role in plant defense mechanisms. They exert direct antimicrobial action, catalyze the mechanical strengthening of cell walls, function as secondary messengers in the superoxide synthase signal pathway and in triggering the hypersensitive response. Although recent studies have unraveled a nature and the mechanisms of the oxidative burst, many questions related to its mode of regulation, its modulation of signaling networks that control growth, development and defense responses remain unanswered.