Cell Wall Peroxidase Research Articles

Changes in cucumber hypocotyl cell wall dynamics caused by Azospirillum brasilense inoculation

We previously reported that Azospirillum brasilense induced a more elastic cell wall and a higher apoplastic water fraction in both wheat coleoptile and flag leaf. These biophysical characteristics could permit increased growth. Knowledge of the biochemical effects the bacteria could elicit in plant cell walls and how these responses change plant physiology is still scarce. The objective of this work was to analyze whether A. brasilense Sp245 inoculation affected elongation and extensibility of growing cucumber (Cucumis sativus) hypocotyls and ionically bound cell wall peroxidase activities. Hypocotyl tip and basal segments were excised from A. brasilense Sp245-inoculated cucumber seedlings growing in darkness under hydroponic conditions. Elongation, cell wall extensibility, cell wall peroxidase activities against ferulic acid and guaiacol and NADH oxidase activities were analyzed. Azospirillum-inoculated cucumber seedlings grew bigger than non-inoculated ones. Dynamic cell wall differences were detected between inoculated and non-inoculated hypocotyls. They included greater acid-induced cell wall extension and in vivo elongation when incubated in distilled water. Although there was no difference between treatments in either region of the hypocotyl NADH oxidase and ferulic acid peroxidase activities were lower in both regions in inoculated seedlings. These lesser activities could be delaying the stiffening of cell wall in inoculated seedlings. These results showed that the cell wall is a target for A. brasilense growth promotion.

Structural Changes of Cell Wall and Lignifying Enzymes Modulations in Bean Roots in Response to Copper Stress

Fourteen-day-old bean seedlings were cultured in nutrient solution containing Cu(2+) ions at various concentrations (50 and 75 microM of CuSO(4)) for 3 days. This excess of copper induced a reduction in the water volume absorbed by the plants. Moreover, this reduction was accompanied by an increase of the amount of copper taken up by the roots. Analysis by native gel electrophoresis of cell wall peroxidase activities in the roots revealed a stimulation of two anionic isoforms (A(2) and A(3)) under cupric stress conditions. Moreover, the activity of phenylalanine ammonia lyase (EC. 4.3.1.5), which plays an important role in plant defense, was enhanced. Copper-treated bean roots showed modifications in the cell walls of various tissues. Label for lignin, callose, and suberin with berberine-aniline blue revealed abnormal cell wall thickenings in the endodermis, the phloem, and the xylem, especially in plants treated with 75 microM CuSO(4).

Ultraviolet Radiation as a Limiting Factor in Leaf Expansion and Development

Reductions in leaf growth are a commonly observed response to ultraviolet radiation, but the underlying mechanisms remain poorly defined. This study examined the response of leaves exposed to a UV environment across a range of organizational scales, including leaf expansion rate, epidermal cell size and number, biomechanical properties, leaf-water relations and activity of cell-wall peroxidases. Two experimental approaches were used; Lettuce (Lactuca sativa L.) plants were propagated under (a) supplementary UV-B (9 kJ m(-2) day(-1)) in controlled environment (CE) conditions, and (b) field conditions, where plants were placed under three horticultural films with differing UV transmissions. In both experiments, UV-B caused the greatest reductions in leaf expansion and final leaf size, with some reductions attributable to UV-A wavelengths. In supplementary UV-B conditions, adaxial cell size was reduced, while in field plants, both cell size and cell number were lower in an increased UV environment, as was the case with abaxial cells in CE plants. Although leaf turgor and leaf extensibility were not affected by UV wavelengths, breaking strain of leaf tissue was decreased under supplementary UV-B. Cell-wall peroxidase activity was increased in both supplementary UV conditions and in the field, where only a zero UV environment showed no upregulation of cell-wall peroxidase.

Effects of Partial Rootzone and Controlled Deficit Irrigation on Growth, Yield and Peroxidase Activities of Tomatoes (Lycopersicon esculentum Mill.)

The aim of the experiment was to examine the application of partial rootzone drying and deficit irrigation on growth and plant development of tomatoes. Potted fresh market tomatoes (Lycopersicon esculentum Mill.) in pots were subjected to partial root zone drying (PRD) and controlled deficit irrigation (CDI) under glasshouse conditions. Roots of plants were remained attached to plants and half the volume divided in one plant and the other half planted in the other adjacent pot. The treatments were: well-watered continually maintained close to field capacity in both pots (control), CDI50 (half the amount of water in control divided equally to both pots with each watering), PRD50 (half the amount of water in control applied to one pot while water was withheld from the other pot until soil water declined to 50-70% the field capacity and then water was applied to the other pot), PRD25 (half the amount of water in control was applied to one pot while water was withheld from the other pots until soil moisture declined to 25-50% field capacity and then water was applied to the other pot) and CDI25 (quarter amount of water in control divided equally to both pots with each watering). Imposing water deficit reduced fruit yield up to 18% in PRD50 and 33% in CDI50 which coincided with an impairment of fruit expansion. The percentage of fruit dry matter and osmotic potential increased in both PRD and CDI compared with the control. The incidence of blossom end rot increased in both CDI and PRD25 compared with the control and PRD50 treatments. Cell wall peroxidase in the epidermal layer of fruit may have a role in cessation of fruit expansion towards fruit maturity under reduced water availability.

Antioxidant status, peroxidase activity, and PR protein transcript levels in ascorbate-deficient Arabidopsis thaliana vtc mutants

Ascorbate is the most abundant small molecule antioxidant in plants and is proposed to function, along with other members of an antioxidant network, in controlling reactive oxygen species. A biochemical and molecular characterization of four ascorbate-deficient (vtc) Arabidopsis thaliana mutants has been carried out to determine if ascorbate deficiency is compensated by changes in the other major antioxidants. Seedlings grown in vitro were used to minimize stress and longer term developmental differences. Comparison was made with the low glutathione cad2 mutant and vtc2-1 treated with D,L-buthionine-[S,R]-sulphoximine to cause combined ascorbate and glutathione deficiency. The pool sizes and oxidation state of ascorbate and glutathione were not altered by deficiency of the other. alpha-Tocopherol and activities of monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, and catalase were little affected. Ascorbate peroxidase activity was higher in vtc1, vtc2-1, and vtc2-2. Ionically bound cell wall peroxidase activity was increased in vtc1, vtc2-1, and vtc4. Supplementation with ascorbate increased cell wall peroxidase activity. 2,6-Dichlorobenzonitrile, an inhibitor of cellulose synthesis, increased cell wall peroxidase activity in the wild type and vtc1. The transcript level of an endochitinase, PR1, and PR2, but not GST6, was increased in vtc1, vtc2-1, and vtc-2-2. Endochitinase transcript levels increased after ascorbate, paraquat, salicylic acid, and UV-C treatment, PR1 after salicylic acid treatment, and PR2 after paraquat and UV-C treatment. Camalexin was higher in vtc1 and the vtc2 alleles. Induction of PR genes, cell wall peroxidase activity, and camalexin in vtc1, vtc2-1, and vtc2-2 suggests that the mutants are affected in pathogen response signalling pathways.

Reactive oxygen species in programmed death of pea guard cells.

Hydrogen peroxide potentiates CN(-)-induced apoptosis of guard cells recorded as destruction of cell nuclei in the epidermis from pea leaves. A still stronger effect was exerted by the addition of H2O2 and NADH, which are the substrates of the plant cell wall peroxidase producing O2*- coupled to the oxidation of NADH. The CN(-)-or (CN(-) + H2O2)-induced destruction of guard cell nuclei was completely removed by nitroblue tetrazolium (NBT) oxidizing O2*- and preventing there-by the subsequent generation of H2O2. The reduced NBT was deposited in the cells as formazan crystals. Cyanide-induced apoptosis was diminished by mannitol and ethanol, which are OH* traps. The dyes Rose Bengal (RB) and tetramethylrhodamine ethyl ester (TMRE) photosensitizing singlet oxygen production suppressed the CN(-)-induced destruction of the cell nuclei in the light. This suppression was removed by exogenous NADH, which reacts with 1O2 yielding O2*-. Incubation of leaf slices with RB in the light lowered the photosynthetic O2 evolution rate and induced the permeability of guard cells for propidium iodide, which cannot pass across intact membranes. Inhibition of photosynthetic O2 evolution by 3-(3',4'-dichlorophenyl)-1,1-dimethylurea or bromoxynil prevented CN(-)-induced apoptosis of guard cells in the light but not in the dark. RB in combination with exogenous NADH caused H2O2 production that was sensitive to NBT and estimated from dichlorofluorescein (DCF) fluorescence. Data on NBT reduction and DCF and TMRE fluorescence obtained using a confocal microscope and data on the NADH-dependent H2O2 production are indicative of generation of reactive oxygen species in the chloroplasts, mitochondria, and nuclear region of guard cells as well as with participation of apoplastic peroxidase. Cyanide inhibited generation of reactive oxygen species in mitochondria and induced their generation in chloroplasts. The results show that H2O2, OH*, and O2*- resources utilized for H2O2 production are involved in apoptosis of guard cells. It is likely that singlet oxygen generated by RB in the light, judging from the permeability of the plasmatic membrane for propidium iodide, makes Photosystem II of chloroplasts inoperative and induces necrosis of the guard cells.

Aluminum-Induced Cell Wall Peroxidase Activity and Lignin Synthesis Are Differentially Regulated by Jasmonate and Nitric Oxide

Cassia tora is an annual legume and cultivated as a traditional medicinal herb for multiple therapies including regulation of blood pressure and blood lipid. Because of naturally occurring acidic soils in southeastern China, this plant species may possess strategies for tolerance to low pH and aluminum toxicity. In the search for the regulatory basis of biochemical response to Al, cell wall-bound peroxidases, including lignin-generated peroxidases and NADH oxidases, were investigated in the root tips of C. tora. Activities of both types of peroxidases significantly increased with Al concentrations. Analysis with native PAGE also demonstrated the strong induction of cell wall peroxidases by Al. The Al-induced increasing activities of peroxidases were closely correlated with lignin accumulation and H 2O 2 production. The biochemical effect of exogenous nitric oxide (NO) and methyl jasmonic acid (MJ) was examined to investigate signal properties and lignin synthesis under Al stress. Application of MJ at 10 microM promoted root sensitivity to Al by activating apoplastic peroxidase activity and accumulating H 2O 2 and lignin, whereas the opposite action was found for NO. The sensitivity of apoplastic peroxidases under Al stress was associated with the cross-talk of MJ and NO signals. The analysis reveals that the activity of lipoxygenase (an enzyme for MJ biosynthesis), with its transcripts increased in Al-exposed roots, was depressed by NO exposure. The effect of MJ on intracellular NO production was also investigated. It is shown that NO staining with 4,5-diaminofluorescein diacetate fluorescence was intensified by Al but was suppressed by MJ. These results suggest that NO and MJ may interplay in signaling the cell wall peroxidase activity and lignin synthesis in the roots exposed to Al.

Cadmium induced oxidative stress and changes in soluble and ionically bound cell wall peroxidase activities in roots of seedling and 3–4 leaf stage plants of Brassica juncea (L.) czern

Metabolic adaptations to heavy metal toxicity in plants are thought to be related with developmental growth stage and the type of metal by which plant is affected. In the present study, changes in ionically bound CWP, soluble peroxidase activity, H(2)O(2) level and Malonaldehyde content in roots of cadmium and copper stressed seedlings and cadmium stressed 3-4 leaf stage plants of Brassica juncea were investigated. Cadmium inhibits root growth and reduces fresh biomass. The reduction in root growth and fresh biomass is correlated with increased lipid peroxidation and reduced tolerance. Treatment with cadmium resulted in an increase in ionically bound CWP activity in roots of seedlings but no significant change in its activity was found in roots of 3-4 leaf stage plants. Increased level of H(2)O(2) in roots of cadmium and copper treated seedlings, show a direct correlation with increased activity of ionically bound CWP. H(2)O(2) level in 3-4 leaf stage plant roots was found to be very low. Soluble peroxidase activity decreased in cadmium (50 and 100 mu-icroM) treated seedlings but it was ineffective to cause any change in its activity in 3-4 leaf stage plants. Copper treated seedlings showed an increase in ionically bound CWP activity, H(2)O(2) level and MDA content. Ascorbic acid (50 mM) pretreated seedlings shows significant decrease in ionically bound CWP activity when exposed to 50 muM cadmium. Hence, it is concluded that inhibition of root growth in Brassica juncea seedlings by cadmium, is associated with CWP catalyzed H(2)O(2) dependent reactions which are involved in metabolic adaptations to heavy-metal stress.

Comparative effects of regulated deficit irrigation (RDI) and partial root-zone drying (PRD) on growth and cell wall peroxidase activity in tomato fruits

The effects of regulated deficit irrigation (RDI) and partial root-zone drying (PRD) on tomato fruit growth and cell wall peroxidase activity in tomato exocarp were investigated in growth chamber conditions. The RDI treatment was 50% of water given to fully irrigated (FI) plants and the PRD treatment was 50% of water of FI plants applied to one half of the root system while the other half dried down, with irrigation shifted when soil water content of the dry side decreased 15–20%. RDI significantly reduced fruit diameter, though PRD reduced fresh weight while having no significant effect on fruit diameter. The activity of peroxidase was significantly higher in RDI and PRD treated plants compared to those of FI. Differences between RDI and PRD were expressed on temporal basis. In the fruits of RDI treated plants peroxidase activity began to increase in the phase when fruit growth started to decline with the peak of enzyme activity of 6.1 HRPEU g −1 FW reached in the phase of mature green fruits when fruit growth rate was minimal. Increase of peroxidase activity in PRD fruits coincided with the ripening phase and the peak of enzyme activity (5.3 HRPEU g −1 FW) was measured at the end of fruit ripening. These data potentially identified contrasting and different roles of tomato exocarp cell wall peroxidase in RDI and PRD treated plants. In RDI treated plants peroxidase may have a role in restricting fruit growth rate, although the increase in enzyme activity during ripening of PRD treated fruit pointed out that peroxidase may also control fruit maturation by inducing more rapid process.

Physiological and biochemical changes at the rootstock-scion interface in graft combinations between Cucurbita rootstocks and a melon scion

SummarySuccess in grafting depends on the identification of a compatible rootstock (RS) that promotes rapid formation of vascular connections between the RS and the scion, and rapid resumption of root and shoot growth. In this study, we used compatible and incompatible Cucurbita rootstocks, with a melon (Cucumis melo L. ‘Arava’) scion, to identify physiological and biochemical factors in the scion-RS interface that could be associated with graft compatibility. Anatomical characterisation of the grafting interface showed that the regeneration and differentiation of vascular elements was similar, at first, in both compatible and incompatible grafted seedlings although, in the latter, a protective layer was formed, but did not interfere with communication between the RS and the scion. Water uptake and sugar distribution between the plant canopy and the roots, measured 14 d after grafting (DAG) were not correlated with compatibility or incompatibility. At 24 DAG, both water uptake and root sugar concentrations decreased significantly in the incompatible RS, reflecting deterioration of the RS. At 24 DAG, part of the RS collapsed, but only in incompatible grafted seedlings. Histochemical staining revealed that superoxide, H2O2, peroxidase (POX) activity, and lignin deposits at the scion-rootstock interface were similar in both compatible and incompatible grafting combinations at 14 DAG; but, at 24 DAG, H2O2 and superoxide levels were higher in the incompatible grafted transplants. In addition, cell-wall POX and superoxide dismutase (SOD) activities were lower in the incompatible RS-scion interface at 14 and 24 DAG. These results suggest that a physical barrier is unlikely to be formed between the incompatible partners early after grafting, but that lower anti-oxidant enzyme activities and higher levels of reactive oxygen species (ROS) in the incompatible RS-scion interface may be responsible for degradation of the grafting zone.

Influence of plant secondary metabolites on in vitro oxidation of methyl ferulate with cell wall peroxidases from lupine apoplast

Ionically bound cell wall peroxidases (POXs) were liberated to intercellular washing fluids (IWFs) and isolated together with other proteins and metabolites present in the apoplast of white lupine (Lupinus albus L. var. Bac) root. After separation of proteins from low molecular weight compounds, activity of peroxidases was monitored in in vitro experiments. Oxidation of methyl ferulate with H2O2 was studied in multi-component mixtures of plant metabolites. Secondary metabolites identified in IWFs or other natural products playing important roles in different physiological processes were applied as modifiers of the dehydrodimerization process during oxidation reactions performed in vitro. These were isoflavones and their conjugates, lupanine representing quinolizidine alkaloids synthesized in lupine, or other natural products such as quercetin, ascorbic, and salicylic acid. The influence of these substances on the oxidation kinetics of methyl ferulate was monitored with liquid chromatography with ultraviolet detection (LC/UV), and identification of compounds was confirmed with the liquid chromatography/mass spectroscopy (LC/MS) system. On the basis of data collected, it was possible to reveal changes in the activities of cell wall POXs. Application of the LC system permitted us to monitor, independently, quantitative changes of two or more reaction products in the mixtures. In multi-component combinations, oxidation yields of methyl ferulate by POXs were modified depending on the actual composition of the reaction mixture. We conclude that various classes of plant secondary metabolites can modify the yield of methyl ferulate oxidation by hydrogen peroxide in the presence of POX, due to interactions with the enzyme's active site (genistein) or radical scavenging properties of metabolites present in the reaction mixture.

Comparison of the removal of 2,4-dichlorophenol and phenol from polluted water, by peroxidases from tomato hairy roots, and protective effect of polyethylene glycol

Multiple efforts have been directed towards optimized processes in which enzymes, like peroxidases, are used to remove phenolic compounds from polluted wastewater. Here we describe the use of peroxidase isoenzymes from tomato hairy roots, which were able to oxidise 2,4-dichlorophenol (2,4-DCP) and phenol from aqueous solutions. This could be an interesting alternative for the removal of these compounds from contaminated sites. We used different enzyme fractions: total peroxidases (TP), ionically bound to cell wall peroxidases (IBP), basic (BP) and acidic peroxidases (AP). We analyzed the optimum conditions of removal, the effect of Polyethyleneglycol (PEG-3350) on the process and on the enzyme activities, to obtain the maximum efficiency. The optimal H 2O 2 concentrations for 2,4-DCP and phenol removal were 1 and 0.1 mM, respectively. TP, IBP and BP showed better removal efficiencies than AP, for both contaminants. The addition of different concentrations (10–100 mg l −1) of PEG-3350 to solutions containing 2,4-DCP showed no effect on the removal efficiencies of the isoenzymes. However, PEG (100 mg l −1) increased the removal efficiency of phenol by BP and IBP fractions. On the other hand, peroxidase activities from BP and IBP fractions were 3 and 13 times higher, respectively, than those detected for the same fractions in phenol treated solutions without PEG. The protective effect of PEG, which depends on the contaminant as well as of the enzyme fraction used, would be important to improve the removal efficiency of phenol by some peroxidase isoenzymes.

The genome of the thermoacidophilic red microalga Galdieria sulphuraria encodes a small family of secreted class III peroxidases that might be involved in cell wall modification

We report the identification of a small family of secreted class III plant peroxidases (Prx) from the genome of the unicellular thermoacidophilic red alga Galdieria sulphuraria (Cyanidiaceae). Apart from two class I ascorbate peroxidases and one cytochrome c peroxidase, the red algal genome encodes four class III plant peroxidases, thus complementing the short list of algal cell wall peroxidases (Passardi et al. in Genomics 89:567-579, 2007). We have characterized the family gene structure, analyzed the extracellular space and cell wall fraction of G. sulphuraria for the presence of peroxidase activity and used shotgun proteomics to identify candidate extracellular peroxidases. For a detailed enzymatic characterization, we have purified a secreted peroxidase (GsPrx04) from the cell-free medium using hydrophobic interaction chromatography. The enzyme proved heat and acid-stable and exhibited an apparent molecular mass of 40 kDa. Comparative genomics between endolithically growing G. sulphuraria and a close relative, the obligatory aquatic, cell wall-less Cyanidioschyzon merolae, revealed that class III peroxidases only occur in the terrestrial microalga, thus supporting the key function of these enzymes in the process of land colonization.

Purification and characterization of cell wall-bound peroxidase from vanilla bean

A cold-active ionically bound cell wall peroxidase was purified from a polyvinylpolypyrrolidone extract of mature vanilla beans by ultra filtration of 10 kDa and gel filtration chromatography on Sephacryl S-200. The M r was 46.5 kDa determined by electrophoresis on SDS–PAGE, while native gel filtration confirmed tetramer enzyme form of approximately 186 kDa. The optimum pH and temperature were 3.8 and 16 °C, respectively, as determined with guaiacol as the substrate ( K m 3.8 mmol/L). The p I was approximately 7.7. The POD was inhibited by 1,4-dithiothreitol, β-mercaptoethanol and sodium azide. The POD showed decreasing activity in the presence of ascorbic acid, NaEDTA and sodium dodecyl sulfate at 1 mmol/L. The enzyme lost 80% of its activity in the presence of 20% ethanol. These results will permit better understanding of POD role in vanilla curing process.

Membrane‐trafficking RabA4c involved in the effect of glycine betaine on recovery from chilling stress in Arabidopsis

Glycine betaine (GB) can confer tolerance to several types of stress at low concentrations, either after application to plants or in transgenics engineered to overproduce GB. Based on earlier studies on levels of GB in plants and evidence for effects on gene expression, we hypothesized that at least part of this effect could be ascribed to the activation of the expression of stress tolerance genes. Using a strategy based on high‐throughput gene expression analysis with microarrays followed by confirmation with northern blots, we identified Arabidopsis genes upregulated in roots that reinforce intracellular processes protecting cells from oxidative damage and others that appear to be involved in reinforcing a scavenging system for reactive oxygen species (ROS) in cell walls. Upregulated genes in roots include those for the membrane‐trafficking RabA4c, the root‐specific NADPH‐dependent ferric reductase (FRO2) localized to the plasma membrane, mitochondrial catalase 2 and the cell wall peroxidase ATP3a. Comparative studies with wild‐type Arabidopsis and knockout mutants for the membrane‐trafficking RabA4c gene demonstrated that the mutants respond only slightly to GB, if at all, compared with wild‐type in relation to root growth recovery after chilling stress, demonstrating the role of RabA4c in relation to the GB effect. The results point toward links between oxidative stress, gene expression, membrane trafficking and scavenging of ROS such as superoxide and hydrogen peroxide in relation to GB effects on chilling tolerance in plants.

Mechanisms of response to ultraviolet-b radiation — A whole plant perspective

Plant responses to ultraviolet (UV) radiation are numerous, resulting in rapid and permanent alteration to numerous aspects of plant form, physiology and biochemistry. Such responses to UV and UV-B (290–320 nm) radiation in particular have been previously studied largely due to concerns over ozone depletion, but a recent refocus towards the effects of environmentally relevant UV-B doses has provided an opportunity to investigate the mechanistic basis for several well defined plant responses. We have characterised some of these underlying mechanisms using a combination of crop species and Arabidopsis mutants, in an effort to build up a model of whole-plant response. (1) The role of UV in regulating leaf growth has been investigated using Lactuca sativa as a model species in a top-down approach, whereby leaf expansion rate, leaf biophysical properties, cell growth and cell wall peroxidase content have been subject to UV-B mediated change. (2) Upregulation of secondary metabolite biosynthesis has also been characterised in L. sativa, with UV absorbing compounds increased according to UV-B, plus leaf anthocyanin (pigment compound) concentration elevated by 60% in plants exposed to the highest UV dose compared to control. (3) The importance of various key pathways to the UV whole plant response are also currently under investigation with a selection of A. thaliana mutants. Such findings will not only add to the understanding of fundamental photobiological responses, but are also currently being successfully integrated into sustainable agronomic practice.

The relationship between the resistance of Aegilops umbellulata Zhuk. seedlings to Septoria nodorum Berk. and peroxidase isozyme pattern

The resistance of Aegilops umbellulata Zhuk. to blotch pathogen Septoria nodorum Berk. has been studied. Cytoplasmic peroxidase activity in normal seedlings could not be used for biochemical prediction of Ae. umbellulata resistance to Septoria blotch. At the same time, isoperoxidases with pI approximately 7.5 and infection-induced activity of anionic isoforms with pI approximately 3.5 were markers of the resistant Aegilops plants. Aegilops resistance to the fungus depended on the activity of cell wall peroxidases.

Cadmium induced changes in cell wall peroxidase isozyme pattern in barley root tips

Changes in peroxidase activity as well as isozyme peroxidase pattern were analyzed in five cell wall (CW) fractions of barley roots exposed to 1mM CdCl<sub>2</sub>for 48 and 72 h. Whereas strong inhibition of peroxidase activity was detected in fraction CW I and weak inhibition in fractions CW II, III and IV, strong activation of peroxidase was observed in fraction V after Cd application. Despite the inhibition of enzyme activity in most CW fractions, induction of several isoperoxidases was discovered after separation on PAGE. In fraction CW I inhibition of one cathodic isoperoxidase and activation of two anodic and two cathodic isoperoxidases was detected. Additional two anodic and one cathodic Cd-induced isozyme appeared in CW II and CW III. Strongly activated anodic isoperoxidase was detected in fraction CW V. Our results demonstrate that monitoring the stress modified peroxidase activity in enzyme extracts using guaiacol as a non-specific peroxidase substrate is not sufficient enough. Since some isozymes can be activated and some inhibited, isozyme pattern analysis is recommended.

Role of Calcium on Phenolic Compounds and Enzymes Related to Lignification in Soybean (Glycine max L.) Root Growth

Changes in soluble and cell wall bound peroxidases activities, phenylalanine ammonia-lyase activity and phenolic compounds and lignin contents in roots of calcium-treated soybean (Glycine max (L.) Merr.) seedlings and their relationships with root growth were investigated. Three-day-old soybean seedlings were cultivated in nutrient solution with or without 0.025–5.0 mM calcium for 24 h. In general, length and fresh and dry weights of roots increased, while activities of enzymes (soluble and cell-wall peroxidases and phenylalanine ammonia-lyase) and phenolic compounds and lignin contents decreased against calcium concentrations. In the absence of calcium, phenylalanine ammonia-lyase and peroxidases activities increased by accumulating phenolic compounds and lignin due to restricted growth of roots. Enhanced calcium supply reduced the production of phenolic compounds and lignification due to low phenylalanine ammonia-lyase and peroxidases activities, reinforcing the essential role of calcium to improve the soybean root growth.

Role of Reactive Oxygen Species in Abiotic and Biotic Stresses in Plants

Biotic and abiotic stresses induce increased formation of reactive oxygen species (ROS) through distinct pathways: pathogen infections activate specific ROS-producing enzymes (i.e. NADPH oxidase, cell wall peroxidases), which results in accumulation of cellular or intercellular ROS, such as superoxide or hydrogen peroxide. Abiotic stresses, on the other hand, cause elevated ROS production principally through an impairment of photosynthetic and respiratory electron transport pathways. Also, these two types of stresses have diverse effects on the antioxidant system of the plant. Results of experiments studying the interaction of abiotic and biotic stresses largely depend on the degree of the applied abiotic stress treatment, the compatible or incompatible host-pathogen interaction and the timing of inoculation in relation to the timing of a preceding abiotic stress treatment.