A. S. Lukatkin

Lipids and proteins—major targets of oxidative modifications in abiotic stressed plants

Stress factors provoke enhanced production of reactive oxygen species (ROS) in plants. ROS that escape antioxidant-mediated scavenging/detoxification react with biomolecules such as cellular lipids and proteins and cause irreversible damage to the structure of these molecules, initiate their oxidation, and subsequently inactivate key cellular functions. The lipid- and protein-oxidation products are considered as the significant oxidative stress biomarkers in stressed plants. Also, there exists an abundance of information on the abiotic stress-mediated elevations in the generation of ROS, and the modulation of lipid and protein oxidation in abiotic stressed plants. However, the available literature reflects a wide information gap on the mechanisms underlying lipid- and protein-oxidation processes, major techniques for the determination of lipid- and protein-oxidation products, and on critical cross-talks among these aspects. Based on recent reports, this article (a) introduces ROS and highlights their relationship with abiotic stress-caused consequences in crop plants, (b) examines critically the various physiological/biochemical aspects of oxidative damage to lipids (membrane lipids) and proteins in stressed crop plants, (c) summarizes the principles of current technologies used to evaluate the extent of lipid and protein oxidation, (d) synthesizes major outcomes of studies on lipid and protein oxidation in plants under abiotic stress, and finally, (e) considers a brief cross-talk on the ROS-accrued lipid and protein oxidation, pointing to the aspects unexplored so far.

Contribution of Oxidative Stress to the Development of Cold-Induced Damage to Leaves of Chilling-Sensitive Plants: 3. Injury of Cell Membranes by Chilling Temperatures

Changes in permeability of cell membranes (judged from electrolyte leakage) were examined on leaves of 7- to 11-day-old seedlings of maize (Zea mays L.), cucumber (Cucumis sativus L.), millet (Panicum miliaceum L.), and on etiolated shoots of potato (Solanum tuberosum L.) immediately after cooling plants for 1–24 h at 2°C and one day after a 24-h chilling treatment. A gradually increasing leakage of ions from the cells was observed upon prolongation of chilling exposure, with the maximum attained by the end of 24-h chilling treatment. The leakage of electrolyte was slightly reduced in the post-treatment period but it was still higher than the electrolyte leakage from the control samples (untreated plants). The cold treatment of chilling-sensitive plants (but not of potato) revealed a positive correlation between the rates of lipid peroxidation, indicative of chilling injury, and the electrolyte efflux (r = 0.61–0.96). The evaluation of plant susceptibility to injury showed that millet and potato plants recovered from the chilling damage in 24 h after the treatment, whereas maize and cucumber plants did not show such a recovery.

Catalase and ascorbate peroxidase—representative H2O2-detoxifying heme enzymes in plants

Plants have to counteract unavoidable stress-caused anomalies such as oxidative stress to sustain their lives and serve heterotrophic organisms including humans. Among major enzymatic antioxidants, catalase (CAT; EC 1.11.1.6) and ascorbate peroxidase (APX; EC 1.11.1.11) are representative heme enzymes meant for metabolizing stress-provoked reactive oxygen species (ROS; such as H2O2) and controlling their potential impacts on cellular metabolism and functions. CAT mainly occurs in peroxisomes and catalyzes the dismutation reaction without requiring any reductant; whereas, APX has a higher affinity for H2O2 and utilizes ascorbate (AsA) as specific electron donor for the reduction of H2O2 into H2O in organelles including chloroplasts, cytosol, mitochondria, and peroxisomes. Literature is extensive on the glutathione-associated H2O2-metabolizing systems in plants. However, discussion is meager or scattered in the literature available on the biochemical and genomic characterization as well as techniques for the assays of CAT and APX and their modulation in plants under abiotic stresses. This paper aims (a) to introduce oxidative stress-causative factors and highlights their relationship with abiotic stresses in plants; (b) to overview structure, occurrence, and significance of CAT and APX in plants; (c) to summarize the principles of current technologies used to assay CAT and APX in plants; (d) to appraise available literature on the modulation of CAT and APX in plants under major abiotic stresses; and finally, (e) to consider a brief cross-talk on the CAT and APX, and this also highlights the aspects unexplored so far.

Cytokinin-like growth regulators mitigate toxic action of zinc and nickel ions on maize seedlings

Maize (Zea mays L.) seedlings grown in water culture in the presence of zinc and nickel ions were used with an effort to alleviate heavy metal toxicity by treating seeds with thidiazuron and kinetin (synthetic growth regulators with cytokinin-like activity). Heavy metals were shown to decrease germinability of seeds, suppress seedling growth, alter membrane permeability, and inhibit the activity of ascorbate peroxidase. Synthetic cytokinin-like agents alleviated deteriorative effects of heavy metals; the extent of alleviation depended on toxicant species and its concentration. The toxic effect of Zn2+ was effectively relieved by kinetin, whereas the Ni2+ toxicity was preferentially alleviated by thidiazuron.

Effect of copper on pro- and antioxidative reactions in radish (Raphanus sativus L.) in vitro and in vivo

The generation of superoxide radicals, lipid peroxidation (as measured by malone dialdehyde formation) and the activity of selected antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase) were assessed in radish (Raphanus sativus L.), in response to elevated concentrations of copper ions in the culture medium in vitro and in vivo. Experiments were performed on 7-day-old seedlings and 5-week-old calluses grown on media supplemented with CuSO4 in concentrations of 10, 100 and 1000μМ. The exposure to elevated Cu concentrations in the medium significantly reduced both callogenesis and the proliferation of radish calluses in vitro. Cu treatment resulted in the increased generation of the superoxide radical (O2(-)) in radish seedlings and calluses indicating the occurrence of oxidative stress in radish cells, whereas the level of lipid peroxidation (LPO) remained unchanged. Both in calluses and in radish seedlings in vivo, the relative level of oxidative stress was maximal at micromolar Cu concentrations and became attenuated with increasing Cu concentrations. Stronger oxidative stress occurred in the radish seedlings in vivo, compared with radish calluses in vitro. The observed lower sensitivity of calluses to Cu-induced oxidative stress and their ability to proliferate upon exposure to Cu concentrations of up to 1000μМ demonstrate the potential of in vitro cell-selection to obtain metal-tolerant radish plant lines.

Treatment with the herbicide TOPIK induces oxidative stress in cereal leaves

Leaf disks as well as intact 7-day-old plants of winter wheat (Triticum aestivum L., cv. Mironovskaya 808), winter rye (Secale cereale L., cv. Estafeta Tatarstana), and maize (Zea mays L., cv. Kollektivnyi 172MV), were treated with the aryloxyphenoxypropionate class herbicide TOPIK, concentrate-emulsion (active ingredient is clodinafop-propargyl (CP), 8-800μg/L), and the effects of short-term action (up to 3h) and long-term aftereffect (up to 3days) on physiological and biochemical indices related to oxidative stress development were studied. The herbicide induced changes, predominantly increases in lipid peroxidation (LPO) intensity, superoxide anion O2(-) generation, total antioxidant activity (AOA), and catalase (CAT) and ascorbate peroxidase (APOX) activity, although the response by plants was nonlinear and depended on the herbicide concentration and duration of treatment. The highest level of generation of O2(-) was observed in the leaves of maize and winter wheat treated by 800μg/L CP, both in the short- and long-term. As TOPIK concentration increased, so too did LPO and AOA in leaves, confirming the presence of oxidative stress in the cells of all three cereals. Antioxidant enzymes were most active in winter rye and wheat, and least active in maize indicating a protective antioxidant mechanism in the first two cereals.

Protective Role of Thidiazuron Treatment on Cucumber Seedlings Exposed to Heavy Metals and Chilling

The action of thidiazuron, a synthetic growth regulator, was studied on 7-day-old cucumber seedlings (Cucumis sativus L., cv. Monastyrskii) exposed to chilling and sublethal concentrations of lead and copper ions. The extent of injury was assessed from the electrolyte leakage from cotyledonary leaves into distilled water. Separate application of each stress factor induced an increase in membrane permeability; however, their combined application caused a weaker response. A preliminary treatment of seedlings with thidiazuron fully or partly prevented the stress-induced stimulation of electrolyte leakage from cotyledon segments. It is concluded that thidiazuron elevates plant resistance to adverse environments.

Transport phenomena of nanoparticles in plants and animals/humans.

The interaction of a plethora nanoparticles with major biota such as plants and animals/humans has been the subject of various multidisciplinary studies with special emphasis on toxicity aspects. However, reports are meager on the transport phenomena of nanoparticles in the plant-animal/human system. Since plants and animals/humans are closely linked via food chain, discussion is imperative on the main processes and mechanisms underlying the transport phenomena of nanoparticles in the plant-animal/human system, which is the main objective of this paper. Based on the literature appraised herein, it is recommended to perform an exhaustive exploration of so far least explored aspects such as reproducibility, predictability, and compliance risks of nanoparticles, and insights into underlying mechanisms in context with their transport phenomenon in the plant-animal/human system. The outcomes of the suggested studies can provide important clues for fetching significant benefits of rapidly expanding nanotechnology to the plant-animal/human health-improvements and protection as well.

Initiation and Development of Chilling Injury in Leaves of Chilling-Sensitive Plants

Based on author’s own and literature data, possible mechanisms of initiation, development, and reparation of cell damages in chilling-sensitive plants during and after chilling are reviewed. A conception of initiation and development of chilling injury, based on a key role of oxidative stress, is put forward. Possible mechanisms of structural and functional changes in cells of chilling-sensitive plants subjected to chilling stress are discussed.

Control of cucumber (Cucumis sativus L.) tolerance to chilling stress—evaluating the role of ascorbic acid and glutathione

Chilling temperatures (1-10 oC) are known to disturb cellular physiology, cause oxidative stress via creating imbalance between generation and metabolism of reactive oxygen species (ROS) leading finally to cell and/or plant death. Owing to known significance of low molecular antioxidants - ascorbic acid (AsA) and glutathione (GSH) in plant stress-tolerance, this work analyzes the role of exogenously applied AsA and GSH in the alleviation of chilling stress (3°C)-impact in cucumber (Cucumis sativus L. cv. Vjaznikowskij 37) plants. Results revealed AsA and GSH concentration dependent metabolism of ROS such as superoxide (O2•‾) and the mitigation of ROS-effects such as lipid peroxidation (LPO) as well as membrane permeability (measured as electrolyte leakage) in C. sativus leaf discs. AsA concentration (750 µM) and GSH (100 µM) exhibited maximum reduction in O2•‾ generation, LPO intensity as well as electrolyte leakage, all of these were increased in cold water (3°C and 25°C)-treated leaf discs. However, AsA, in particular, had a pronounced antioxidative effect, more expressed in case of leaf discs during chilling (3°C); whereas, at temperature 25°C, some AsA concentrations (such as 50 and 100 mM AsA) exhibited a prooxidative effect that requires molecular-genetic studies. Overall, it is inferred that AsA and GSH have high potential for sustainably increasing chilling-resistance in plants.