Several reactive oxygen species (ROS) are continuously produced in plants as byproducts of aerobic metabolism. Depending on the nature of the ROS species, some are highly toxic and rapidly detoxified by various cellular enzymatic and nonenzymatic mechanisms. Whereas plants are surfeited with mechanisms to combat increased ROS levels during abiotic stress conditions, in other circumstances plants appear to purposefully generate ROS as signaling molecules to control various processes including pathogen defense, programmed cell death, and stomatal behavior. This review describes the mechanisms of ROS generation and removal in plants during development and under biotic and abiotic stress conditions. New insights into the complexity and roles that ROS play in plants have come from genetic analyses of ROS detoxifying and signaling mutants. Considering recent ROS-induced genome-wide expression analyses, the possible functions and mechanisms for ROS sensing and signaling in plants are compared with those in animals and yeast.

REACTIVE OXYGEN SPECIES: Metabolism, Oxidative Stress, and Signal Transduction

Water deficit and salinity, especially under high light intensity or in combination with other stresses, disrupt photosynthesis and increase photorespiration, altering the normal homeostasis of cells and cause an increased production of reactive oxygen species (ROS). ROS play a dual role in the response of plants to abiotic stresses functioning as toxic by-products of stress metabolism, as well as important signal transduction molecules. In this review, we provide an overview of ROS homeostasis and signalling in response to drought and salt stresses and discuss the current understanding of ROS involvement in stress sensing, stress signalling and regulation of acclimation responses.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2009.02041.x

Reactive oxygen species homeostasis and signalling during drought and salinity stresses

Low temperature, drought, and high salinity are common stress conditions that adversely affect plant growth and crop production. The cellular and molecular responses of plants to environmental stress have been studied intensively ([Thomashow, 1999][1]; [Hasegawa et al., 2000][2]). Understanding the

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Cell Signaling during Cold, Drought, and Salt Stress

Abscisic acid (ABA) regulates many agronomically important aspects of plant development, including the synthesis of seed storage proteins and lipids, the promotion of seed desiccation tolerance and dormancy, and the inhibition of the phase transitions from embryonic to germinative growth and from

/pdf/abscisic-acid-signaling-in-seeds-and-seedlings-21b3w9tc2t.pdf

Abscisic Acid Signaling in Seeds and Seedlings

While the chemical nature of reactive oxygen species (ROS) dictates that they are potentially harmful to cells, recent genetic evidence suggests that in planta purely physicochemical damage may be much more limited than previously thought. The most potentially deleterious effect of ROS under most conditions is that at high concentrations they trigger genetically programmed cell suicide events. Moreover, because plants use ROS as second messengers in signal transduction cascades in processes as diverse as mitosis, tropisms and cell death, their accumulation is crucial to plant development as well as defence. Direct ROS signal transduction will ensue only if ROS escape destruction by antioxidants or are otherwise consumed in a ROS cascade. Thus, the major low molecular weight antioxidants determine the specificity of the signal. They are also themselves signal-transducing molecules that can either signal independently or further transmit ROS signals. The moment has come to re-evaluate the concept of oxidative stress. In contrast to this pejorative or negative term, implying a state to be avoided, we propose that the syndrome would be more usefully described as 'oxidative signalling', that is, an important and critical function associated with the mechanisms by which plant cells sense the environment and make appropriate adjustments to gene expression, metabolism and physiology.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-3040.2005.01327.x

Oxidant and antioxidant signalling in plants: a re-evaluation of the concept of oxidative stress in a physiological context

One of the most important functions of the plant hormone abscisic acid (ABA) is to induce stomatal closure by reducing the turgor of guard cells under water deficit. Under environmental stresses, hydrogen peroxide (H 2 O 2 ), an active oxygen species, is widely generated in many biological systems. Here, using an epidermal strip bioassay and laser-scanning confocal microscopy, we provide evidence that H 2 O 2 may function as an intermediate in ABA signaling in Vicia faba guard cells. H 2 O 2 inhibited induced closure of stomata, and this effect was reversed by ascorbic acid at concentrations lower than 10 −5 m. Further, ABA-induced stomatal closure also was abolished partly by addition of exogenous catalase (CAT) and diphenylene iodonium (DPI), which are an H 2 O 2 scavenger and an NADPH oxidase inhibitor, respectively. Time course experiments of single-cell assays based on the fluorescent probe dichlorofluorescein showed that the generation of H 2 O 2 was dependent on ABA concentration and an increase in the fluorescence intensity of the chloroplast occurred significantly earlier than within the other regions of guard cells. The ABA-induced change in fluorescence intensity in guard cells was abolished by the application of CAT and DPI. In addition, ABA microinjected into guard cells markedly induced H 2 O 2 production, which preceded stomatal closure. These effects were abolished by CAT or DPI micro-injection. Our results suggest that guard cells treated with ABA may close the stomata via a pathway with H 2 O 2 production involved, and H 2 O 2 may be an intermediate in ABA signaling.

Xiao Zhang

Papers

Hydrogen Peroxide Is Involved in Abscisic Acid-Induced Stomatal Closure in Vicia faba