Reactive oxygen species (ROS) are produced as a normal product of plant cellular metabolism. Various environmental stresses lead to excessive production of ROS causing progressive oxidative damage and ultimately cell death. Despite their destructive activity, they are well-described second messengers in a variety of cellular processes, including conferment of tolerance to various environmental stresses. Whether ROS would serve as signaling molecules or could cause oxidative damage to the tissues depends on the delicate equilibrium between ROS production, and their scavenging. Efficient scavenging of ROS produced during various environmental stresses requires the action of several nonenzymatic as well as enzymatic antioxidants present in the tissues. In this paper, we describe the generation, sites of production and role of ROS as messenger molecules as well as inducers of oxidative damage. Further, the antioxidative defense mechanisms operating in the cells for scavenging of ROS overproduced under various stressful conditions of the environment have been discussed in detail.

https://downloads.hindawi.com/archive/2012/217037.pdf

Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants under Stressful Conditions

Numerous studies are reviewed of the plasma membrane in relation to freezing injury and cold acclimation. An attempt is made to explore the nature of freezing injury of plants on which to formulate a mechanism(s) of injury and how the biochemical changes occurring during cold acclimation can be accurately assessed. Although it is likely that all cellular membranes are susceptible to freezing injury, there has been a tendency to establish a hierarchy of injury to various cellular membranes. Nevertheless, it is the plasma membrane that plays a central role in the behavior of the a cell during a freeze-thaw cycle. 247 references.

Role of the Plasma Membrane in Freezing Injury and Cold Acclimation

Frost survival of plants

1. The overall implications of biological stress.- 2. Oxidative stress.- 3. Salt stress.- 4. Chilling stress.- 5. Freezing stress.- 6. Desiccation.- 7. Water and drought stress.- 8. Heat stress.- 9. Anaerobic stress - flooding and ice-encasement.- 10. Environmental pollution stress.- Epilogue.

Stress and stress coping in cultivated plants

Effects of heat acclimation pretreatment on changes of membrane lipid peroxidation, antioxidant metabolites, and ultrastructure of chloroplasts in two cool-season turfgrass species under heat stress

Chilling temperatures increase the amounts of potentially lethal toxic oxygen compounds present within plants. These toxic oxygen compounds can be scavenged by antioxidant compounds such as ascorbate and β-carotene. Three developmental stages (first, third and fifth leaf) of four inbred lines of maize (Zea mays L.) exhibiting differential sensitivity to chilling were examined in order to determine if the chilling-sensitive line had lower concentrations of antioxidant compounds than did the tolerant lines. Plants were exposed to one of three treatments: (1) control (25°C constant), (2) control treatment plus a short-term chilling exposure of 11°C one day prior to harvesting, and (3) long-term (11°C constant) chilling exposure. Total ascorbate, total glutathione, β-carotene, α-tocopherol and chlorophyll contents were quantified, and ratios of dehydroascorbate/ascorbate and reduced/oxidized glutathione were determined. Lower concentrations of β-carotene were found in the chilling-sensitive relative to those in the chilling-tolerant lines for the first-leaf stage under both short- and long-term chilling treatments. Concentrations of total ascorbate and glutathione and β-carotene in the chilling-sensitive line increased as the chilling treatment progressed and as the plants developed until they ultimately became either significantly higher or no different relative to the tolerant lines. Results suggest that this sensitive line became less sensitive to chilling-induced oxidative stress with development.

Antioxidant compound responses to chilling stress in differentially sensitive inbred maize lines

Antioxidant enzyme activities were determined at the first, third and fifth leaf stages of four inbred lines of maize (Zea mays L.) exhibiting differential sensitivity to chilling. Plants were exposed to a photoperiod of 16:8 L: D for one of three treatments: (a) control (25°C), (b) control treatment plus an exposure to a short-term chilling shock (11°C 1d prior to harvesting), and (c) long-term (11 °C constant) chilling exposure. Catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (ASPX; EC 1.11.1.11), superoxide dismutase (SOD; EC 1.15.1.1), glutathione reductase (GR; EC 1.6.4.2), and monodehydroascorbate reductase (MDHAR; EC 1.6.5.4) activities were assessed. Reducing and non-reducing sugars and starch concentrations were determined as general metabolic indicators of stress. Reduced activities of CAT, ASPX, and MDHAR may contribute to limiting chilling tolerance at the early stages of development in maize. Changes in levels of sugar and starch indicated a more rapid disruption of carbohydrate utilization in comparison to photosynthetic rates in the chilling-sensitive line under short-term chilling shocks and suggested a greater degree of acclimation in the tolerant lines over longer periods of chilling.

Antioxidant enzyme responses to chilling stress in differentially sensitive inbred maize lines

Chilling sensitive species often have lower antioxidant capacities than do tolerant species. This study was conducted to determine if antioxidant capacities and carbohydrate concentrations would be useful in a proposed screening technique for chilling sensitivity in maize (Zea mays L.). Leaves of 12 maize hybrids exhibiting differential sensitivity to chilling were harvested at the third-leaf stage under either (i) a constant 25°C control regime or (ii) the control regime plus a short-term chilling shock of 11°C for 1 d prior to harvesting. Catalase (CAT; EC 1.11.1.6), monodehydroascorbate reductase (MDHAR; EC 1.6.5.4), and ascorbate peroxidase (ASPX; EC 1.11.1.11) activities were assessed. Carbohydrate levels were determined as general metabolic indicators of chilling stress. The chill/ control ratios of CAT, MDHAR, and ASPX were lowest and concentrations of carbohydrates highest in the most chilling sensitive hybrids. Differences between hybrids in antioxidant capacities to detoxify toxic oxygen compounds may be important in differential chilling sensitivity. The higher chill/control ratios of carbohydrates in the sensitive hybrids after chilling indicated that their rate of assimilate utilization was reduced by the chilling treatment more so than those of the chilling tolerant hybrids. Activities of CAT, MDHAR, and ASPX and concentrations of carbohydrates would thus make excellent indicators of chilling stress in a screening technique for chilling sensitivity of maize.

Antioxidant Enzyme and Compound Responses to Chilling Stress and their Combining Abilities in Differentially Sensitive Maize Hybrids

Ice encasement damages cold-hardened winter wheat without major disruption of cellular organelles. CO(2) accumulates during total ice encasement to higher levels in Kharkov than in less hardy Fredrick wheat. Partial ice encasement and exposure to a nitrogen atmosphere at -1 C allows greater CO(2) accumulation but neither treatment is as damaging as total ice encasement. Lactic acid accumulates to low levels only during the 1st day of encasement and thereafter remains constant. Exposure of plants to a combination of 50% CO(2) and 5% ethanol reduces survival, with a cultivar difference similar to that found in ice-encased plants. Plants in CO(2) and ethanol show a proliferation of membranes and nuclear condensation similar to that in cells of ice-encased plants. Permeability increases markedly in the presence of CO(2) and ethanol, to levels similar to or greater than those of iced plants. Ethanol alone does not increase permeability but in combination with CO(2) raises permeability of the less hardy Fredrick, although not of Kharkov, but reduces survival of both cultivars. A comparison of the endogenous levels of ethanol, CO(2), and lactic acid at the 50% kill point of plants due to ice encasement or due to externally supplied metabolite indicates that only CO(2) accumulates to independently toxic levels. Permeability and ultrastructural evidence suggest that CO(2) and ethanol in combination are the agents reducing plant viability during ice encasement.

/pdf/toxicity-of-anaerobic-metabolites-accumulating-in-winter-1h0q39m2yq.pdf

Toxicity of Anaerobic Metabolites Accumulating in Winter Wheat Seedlings during Ice Encasement

The effect of temperature on respiration of mitochondria and tissue segments from three wheat (Triticum aestivum L.) and one rye (Secale cereale L.) cultivar grown at 2 and 24 C has been examined. Discontinuities in Arrhenius plots of respiratory activity against temperature were observed for mitochondria and tissue segments from seedlings grown at both temperatures. The rates of respiration decreased abruptly below the transition temperatures, resulting in increased energy of activation values for respiration. Transition temperatures were observed from 6 to 10 C during tissue segment respiration, and from 10 to 14 C during respiration by isolated mitochondria. Respiratory control and efficiency of phosphorylation were not affected markedly by either reaction temperature or growth temperature of the seedlings. No correlation was observed between the cold hardiness of the cultivars and the temperature at which structural transitions occurred in the mitochondria. Dry matter content of the seedlings increased markedly during growth at 2 C, but no appreciable changes in the levels of mitochondrial protein were observed. The results support the view that changes other than fatty acid unsaturation are involved in the abrupt change in mitochondrial membrane properties at low temperature.

/pdf/effect-of-temperature-on-respiration-of-mitochondria-and-4sh3kfydaa.pdf

Chris J. Andrews

Papers

Antioxidant compound responses to chilling stress in differentially sensitive inbred maize lines

Antioxidant enzyme responses to chilling stress in differentially sensitive inbred maize lines

Antioxidant Enzyme and Compound Responses to Chilling Stress and their Combining Abilities in Differentially Sensitive Maize Hybrids

Toxicity of Anaerobic Metabolites Accumulating in Winter Wheat Seedlings during Ice Encasement

Effect of Temperature on Respiration of Mitochondria and Shoot Segments from Cold hardened and Nonhardened Wheat and Rye Seedlings