Peroxidase Activity In Plants Research Articles

Unlocking the Potential of Fertilizer and Pesticide Integration: Investigating the Promoting Effect of Organic Water-Soluble Fertilizers on Pesticide Degradation for Sustainable Agriculture

Abstract: 
 In the present study, the dynamic degradation profile of the pesticide acaricide was investigated in the presence of varying concentrations of organic water-soluble fertilizers. Field experiments were carried out to assess the influence of organic water-soluble fertilizers on pesticide degradation rates. It was found that, under specific conditions, organic water-soluble fertilizers can promote the degradation of pesticides. To elucidate the factors responsible for this observation, both biological and abiotic aspects were examined. With regard to the biological factors, plant peroxidase activity was analyzed at different concentration levels of organic water-soluble fertilizers during the course of the field experiments. It was determined that organic water-soluble fertilizers can enhance peroxidase activity. Concerning the abiotic factors, high-pressure mercury lamps were utilized in ultraviolet (UV) degradation experiments on the acaricide, incorporating various concentrations of organic water-soluble fertilizers. Furthermore, washing experiments simulating rainwater effects were conducted on representative vegetable species from the Brassicaceae, Asteraceae, Amaranthaceae and Amaranthus tricolor families. The results of the UV degradation experiment showed no significant difference in the acaricide degradation rate, regardless of the presence or absence of organic water-soluble fertilizers. Additionally, the washing experiment demonstrated the effectiveness of organic water-soluble fertilizers in reducing pesticide residues in common vegetable varieties. The findings of this study have important implications for pesticide management and agricultural practices, emphasizing the potential of organic water-soluble fertilizers in facilitating the degradation of pesticides and minimizing their environmental impact.

Resistance against phomopsis leaf blight disease induced by potassium salts in strawberry plants

BackgroundGrowing interest of strawberry cultivation in Egypt necessitates more efforts towards its severe phomopsis leaf blight disease caused by Phomopsis obscurans. Synthetic fungicides could control this fungus but due to their critical impact on human beings and the environment, we are in dire need of safe alternatives for its control. Therefore, the leverage of the potassium bicarbonate and dipotassium phosphate on P. obscurans suppression on strawberry plants was examined.ResultsFull inhibition of the fungal linear growth was achieved at the highest concentration (2%) of the two salts. Under field conditions, 87.5, 81.3, and 81.3% were the best decreases in disease severity gained by the two salts at 2% of both salts and the fungicide Amstar, respectively. Potassium bicarbonate at 1.5% reduced severity by 68.8%. Concentrations 1, 1.5, and 2% of each salt considerably enhanced strawberry yield. The increases were 66.7 and 61.7%, at 2% concentration by the two salts, respectively. Increments by 126.7 and 150% of peroxidase activity in plant leaves and by 140 and 148% of chitinase activity were noted by the two salts, respectively, at 2%.ConclusionsThe examined bicarbonate and phosphate salts could suppress P. obscurans growth and spread. The more the used salt concentration, the better it suppresses the fungal growth with consequent effect on the plants which apparently promoted their field yield. Potential implications of the two salts on enhancing activities of the two enzymes reflected their role in suppressing the disease. Further research is needed to integrate these salts in management strategies of P. obscurans in Egypt to foster strawberry yield utilizing ecofriendly approaches.

Phytotoxicity of gaseous limit and aromatic hydrocarbons in relation to some agricultural plants

The authors of the article determine the phytoxicity of aromatic hydrocarbons in various concentrations in relation to some agricultural plants and the ability of these plants to accumulate hydrocarbons. This is done for the first time on the basis of field studies of plantings at different distances from the enterprise for the production of carbon black, which is a source of gaseous saturated and aromatic hydrocarbons, as well as after exposure of these mixtures to methane, phenol, benzene and toluene. The objects of study were Phaseolus vulgaris, Hordeum vulgare and soft spring wheat called “Memory of Aziev”. Statistically significant changes in the pigment complex of plants, expressed in a decrease in the content of pigments and carotenoids, an increase in the ratio of b and a chlorophyll under the action of hydrocarbons were revealed. The activity of the polyphenol oxidase enzyme tended to initially increase, in response to pollution, and to a subsequent decrease under the action of higher concentrations and high toxicity of the gas. Plant peroxidase activity increased 1.5–7 times with an increase in the concentration of toxin in comparison with the control analogues. According to the degree of phytotoxicity, the studied gases are arranged in the following sequence: phenol > mixture of aromatic hydrocarbons > benzene > toluene > methane. Phaseolus vulgaris turned out to be the most sensitive to the action of hydrocarbons, and also capable of active absorption of hydrocarbons.

Effect of Pseudomonas Bacteria on Peroxidase Activity in Wheat Plants when Infected with Bipolaris sorokiniana

We investigated the effect of treating soft wheat seeds (Triticum aestivum L.) with two Pseudomonas bacteria strains, isolated from earthworm coprolites, showing a significant antifungal and growth-promoting action in preliminary screening on the activity of guaiacol-dependant peroxidase under phytopathogenic load in the presence of Bipolaris sorokiniana (Sacc.) Shoemaker as a mechanism for inducing plant resistance to the pathogen. We established a statistically significant decrease (P < 0.05) in root rot disease incidence and severity during bacterization, which is indicative both of antifungal activity of the used bacterial isolates and of their successful colonizing the rhizosphere of wheat plants. We noted a response of free and weakly bound peroxidase of wheat plants to infection with B. sorokiniana: the enzyme activity increased during pathogenesis. Bacterization also increased peroxidase activity in plant leaves and roots, the greatest differences from non-bacterized plants being observed in wheat roots in the presence of the pathogen. We detected a direct link between peroxidase activity in wheat roots and leaf tissues in the absence of the pathogen and the feedback between peroxidase activity and plant infestation by the root rot pathogen. In the presence of the phytopathogen, there is a lack of correlation between peroxidase activity in wheat roots and leaves, and there is a shift of activity towards its increase in roots, which plays an important role in the development of systemic resistance against the root rot pathogen that penetrates into plants through the roots and root collar.

Analysis of Changes of POD Activity of Indoor Plants under the Stress of Benzene Pollution

Benzene is the main pollutant of indoor chemical pollution, which is severely threatening the human-being’s daily life. To find a reasonable and safety method to control the indoor benzene pollution has become an urgent issue. The activity of peroxidase in plants is an important basis of judging the resistance ability of plants to benzene pollution stress. The study made 8 kinds of shade tolerant foliage-plants live under benzene stress. The results show that both of the benzene and the plant species and the collaboration of them have an significant effect on plant POD activity, the resistance capability of Sansevieria trifasciata is the best, with Scindapsus aureun least.

The adaptability of a wetland plant species Myriophyllum aquaticum to different nitrogen forms and nitrogen removal efficiency in constructed wetlands.

Constructed wetlands (CWs) cultivated with Myriophyllum aquaticum showed great potential for total nitrogen (TN) removal from aquatic ecosystems in previous studies. To evaluate the growth characteristics, photosynthetic pigment content, and antioxidative responses of M. aquaticum, as well as its TN removal efficiency in CWs, M. aquaticum was treated with different levels of ammonium (NH4+) and nitrate (NO3-) for 28days. The results indicated that M. aquaticum had strong nitrogen stress tolerance and was more likely to be suppressed by high levels of NH4+ than NO3-. High levels of NH4+ also led to inhibition of synthesis of photosynthetic pigments and increased peroxidase activity in plant leaves, which was not found in the NO3- treatments. High levels of both NH4+ and NO3- generated obvious oxidative stress through elevation of malondialdehyde content while decreasing superoxide dismutase activity in the early stage. A sustainable increase of TN removal efficiency in most of the CWs indicated that M. aquaticum was a candidate species for treating wastewater with high levels of nitrogen because of its higher tolerance for NH4+ and NO3- stress. However, the increase of TN removal efficiency was hindered in the late stage when treated with high levels of NH4+ of 26 and 36mmol/L, indicating that its tolerance to NH4+ stress might have a threshold. The results of this study will enrich the studies on detoxification of high ammonium ion content in NH4+-tolerant submerged plants and supply valuable reference data for proper vegetation of M. aquaticum in CWs.

Agronomic application of olive mill wastewater: Effects on maize production and soil properties

This study investigates the effect of direct amendment of olive mill wastewater (OMW) on the fertility of soil, described as poor in the area of Marrakech (semi-arid region) in Morocco. The treated plots were amended with untreated OMW generated by a traditional extraction process at the amount of 10 L/m2/year during two consecutive years. Results of these two years treatments with crude OMW at relatively high dose reveal an important increase in soil physicochemical characteristics, namely electric conductivity (EC), Na+, K+, phosphorus, nitrogen, organic matter and soluble phenolic compounds. EC of treated soil was enhanced from 0.34 to 2.91 mS/cm as compared to the control soil. After spreading OMW in soil, the amounts of its nutritive elements increased by 81% for nitrogen, 66% for phosphorus and 88% for potassium. The accumulation of phenolic compounds and the increase of total peroxidase activity in plants provide evidence of their protective role against the physiological stress induced by OMW. However, this enrichment in mineral and nutritive elements decreased three months after OMW application, revealing OMW biodegradation in the studied calcareous soil. In parallel, an increase in the contents of the soluble phenolic compounds on the upper layer of soil was denoted and maize plants growth was efficiently raised. Significant amelioration was obtained notably in terms of fresh and dry weight of leaves, leaves area, spikes fresh and dry weight, 100 seeds weight and straw yield (37, 54, 27, 24, 14 and 9% respectively). Along with the correct choice of convenient soils notably calcareous ones and tolerant crops such as maize, this method could constitute an efficient approach for avoiding problems attributed to the uncontrolled disposal of these effluents and an effective strategy to regenerate degraded soils and represents an economical alternative that provides a local fertilizer.

Effects of silicon and drought stress on biochemical characteristics of leaves of upland rice cultivars

Silicon (Si) has beneficial effects on many crops, mainly under biotic and abiotic stress. Silicon can affect biochemical, physiological, and photosynthetic processes and, consequently, reduce drought stress. However, the effects of Si on rice (Oryza sativa L.) plants under drought stress are not well known. The objective of this study was to evaluate the effects of supplemental Si on proline content and peroxidase activity in upland rice plants in the presence and absence of drought stress. The experiment was conducted under greenhouse conditions and was arranged in completely randomized blocks in a 2 x 2 x 2 factorial scheme. Treatments comprised combinations of (1) presence or absence of Si supply (0 or 350 kg ha-1 of Si), (2) presence or absence of a water deficit (-0.050 MPa or -0.025 MPa soil water potential values, respectively), and (3) two upland rice cultivars: Caiapo (traditional type) and Maravilha (modern type), with eight replications. Under water stress conditions, silicon fertilization reduced the proline content in the vegetative and reproductive phases of upland rice plants and increased peroxidase activity in the plants' reproductive phase, which could be indicative of stress tolerance.

Letter to Editor: Antioxidant Action of Phenols under Heavy Metal Stress

The conception of antioxidant action of phenolic compounds is not novel. There have been many reports of induced accumulation of phenolic compounds and peroxidase activity in plants treated with high concentrations of metals.1 Antioxidant action of phenolic compounds is due to their high tendency to chelate metals. Phenolics possess hydroxyl and carboxyl groups, able to bind particularly iron and copper. The roots of many plants exposed to heavy metals exude high levels of phenolics. They may inactivate iron ions by chelating and additionally suppressing the superoxide-driven Fenton reaction, which is believed to be the most important source of ROS. Tannin-rich plants such as tea, which are tolerant to Mn excess, are protected by the direct chelatation of Mn. Direct chelation, or binding to polyphenols, was observed with methanol extracts of rhizome polyphenols from Nympheae for molecules, and the number and position of the hydroxyl group in the molecules. 2

Enzymatic Modification of Flaxseed Fibers

Flaxseed (Linum usitatissimum L.) fibers were modified by oxidoreductive and cellulolytic enzymes. The lignin amount and intrinsic plant peroxidase activity was evaluated by histochemical and spectrophotometric assays. Peroxidase activity was not found from bast fibers. The flaxseed fibers were further separated and treated with laccase to conjugate the model compounds, that is, the hydrophobic gallate molecules on fiber surfaces. Laccase was able to slowly oxidize fiber-conjugated phenolics, but no fundamental changes in fiber cell surface structure or notable coupling of the applied hydrophobic gallate molecules onto the fibers occurred, as revealed by Fourier transform infrared spectroscopy. The reactivity of the mature fibers was further investigated using cellulolytic enzymes. Cellobiohydrolase (CBH) and endoglucanase (EG)-rich enzyme preparations were applied to reach a hydrolysis degree of 1-6% (of the fiber dry matter) using a standard enzyme dosage. The CBH mixture altered the fiber surface morphology distinctly, and SEM images illustrated fibers in which the cellulose fibrils seemed to be loosened and partially hydrolyzed. In contrast, the effect of the EG-rich preparation without CBH activity was notable on the fiber surface, polishing the surfaces. The cellulolytic treatments were potentially interesting for specific enzymatic modifications of flax fiber surfaces, whereas the approach to use oxidoreductive enzyme treatments on mature linseed fibers offered little potential, obviously due to the low lignin content of the fibers.

Effect of industrial wastewater ontotal protein and the peroxidase activity in plants

The aim of this study is to investigate the effects of industrial wastewaters on protein and the peroxidase activity in Lycopersicon esculentum Mill., Capsicum annuum L., Phaseolus vulgaris L. and Vicia faba L. Industrial wastewaters were taken from Dardanel Fisheries Company, Tekel alcoholic drinks companies’ wastewater treatment plants and from one station which is located in the middle of the Sarýcay River. Wastewaters were applied to 6 weeks old plants with directly irrigation water. Physiological changes in the plants were observed by the means of measuring the protein and enzyme activity. The largest increase in protein was observed as 190.9 and 136.3% in V. faba treated with Sarýcay River water and Tekel wastewater, respectively. In P. vulgaris which was treated with Dardanel wastewater, the total protein amount increased by 84% compared to control plants. After the wastewater treatment, the peroxidase activity decreased in all plants. The largest peroxidase decrease was 80% in L. esculentum treated with Tekel wastewater. In P. vulgaris, peroxidase decreased by 59 and 51% when treated with Dardanel wastewater and Sarýcay River water, respectively. It was concluded that the increase in total protein amount and the decrease in peroxidase activity demonstrated the industrial wastewater’s blocking effects on plants defense systems.

Indução de resistência a doenças foliares em tomateiro por indutores biótico (Bacillus subtilis) e abiótico (Acibenzolar-S-Metil)

O objetivo deste trabalho foi investigar se doenças foliares do tomateiro (Lycopersicon esculentum) podem ser afetadas pela indução de resistência proporcionada pela aplicação de Bacillus subtilis, no solo e nas folhas e aplicação via foliar de acibenzolar-S-metil. A fim de investigar o modo de ação envolvido no controle foi avaliada a atividade de peroxidases nas folhas do tomateiro tratado com os indutores biótico e abiótico. Para se avaliar a severidade das doenças foliares foi avaliado o número de folhas de tomate com algum sintoma de doença e determinado o percentual de folhas doentes em relação ao total de folhas por planta. O aumento significativo da concentração de peroxidases nas plantas tratadas com os indutores, assim como a ausência de controle das doenças no tratamento com pulverização direta de B. subtilis nas folhas, são evidências que sugerem que o mecanismo de controle das doenças em questão está relacionado à resistência induzida.

Indução de resistência em tomateiro por extratos aquosos de Lentinula edodes e Agaricus blazei contra Ralstonia solanacearum

O presente trabalho foi conduzido com o objetivo de avaliar o efeito dos extratos aquosos dos cogumelos Lentinula edodes e Agaricus blazei e do indutor de resistência acibenzolar-S-metil (ASM) no controle da murcha bacteriana em tomate (Lycopersicon esculentum Mill.), bem como investigar o modo de ação destes produtos na atividade protetora, através de alterações na atividade de determinadas enzimas. Extratos aquosos dos cogumelos e o ASM foram testados na inibição do crescimento da bactéria in vitro. Em casa-de-vegetação, plantas foram tratadas com diferentes doses dos extratos e com ASM (0,05 g/L), dois dias antes da inoculação. As avaliações foram efetuadas com base na severidade da doença e determinação da atividade de algumas enzimas. Os isolados de A. blazei e L. edodes, bem como o ASM, não exerceram efeito inibitório direto no crescimento da bactéria. Quanto à indução de resistência, o isolado Le-96/17 de L. edodes na concentração de 10 % (v/v) e o ASM reduziram significativamente a ocorrência de murcha. As atividades de quitinase, fenilalanina amônia-liase e polifenoloxidase não foram alteradas para a maioria dos tratamentos, porém foi constatado um aumento na atividade de quitinase nas plantas tratadas com ASM. Para a peroxidase, os tratamentos ASM, Abl-26 e Le-96/17 ocasionaram aumentos na atividade da enzima e, com base nos resultados, o cogumelo L. edodes e o ASM apresentam potencial para reduzir a murcha bacteriana provavelmente através da indução de resistência.

Friend or Foe?: A Plant's Induced Response to an Omnivore

Omnivorous natural enemies of herbivores consume plant-based resources and may elicit induced resistance in their host plant. A greater induction threshold for damage produced by omnivorous predators than for strict herbivores might be expected if omnivore performance is enhanced on noninduced plants, allowing them to reduce future levels of herbivory. Currently, it is not known if a plant responds to feeding by omnivorous predators and by herbivores similarly. To examine this question, we chose herbivore and omnivore species that produce the same kind of quantifiable damage to cotton leaves, enabling us to control statistically for the intensity of plant damage, and ask whether plant responses differed depending on the identity of the damaging species. We first compared changes in plant peroxidase activity, gossypol gland number and density, and leaf area in response to feeding by the spider mite Tetranychus turkestani (Ugarov and Nikolski) (an herbivore) and by one of the mite’s principal natural enemies, the western flower thrips Frankliniella occidentalis (Pergande) (an omnivore). Both species increased the activity of peroxidase, but when we controlled for the amount of damage, the peroxidase activity of mite-damaged plants was higher than that of thrips-damaged plants. We also found that thrips, but not spider mites, increased the density of gossypol glands in the second true leaf. In a second experiment we included an additional herbivore, the bean thrips Caliothrips fasciatus (Pergande), to see if the different responses of cotton to thrips and mite herbivory we first observed were attributable to differences in trophic function (herbivore versus omnivore) or to other differences in feeding generated by thrips versus mites. Cotton plants exhibited the same pattern of induced responses (elevated peroxidase, increased number of glands, reduced leaf area) to herbivory generated by the bean thrips (an herbivore) and western flower thrips (an omnivore), suggesting that trophic function was not a key determinant of plant response. Thrips-damaged plants again showed a significantly higher density of gossypol glands than did mite-damaged plants. Overall, our results suggest that (1) an omnivorous predator systemically induces resistance traits in cotton and (2) whereas there is evidence of taxonomic specificity (thrips versus mites), there is little support for trophic specificity (herbivorous thrips versus omnivorous thrips) in the elicitation of induced responses.

Friend or Foe?: A Plant’s Induced Response to an Omnivore

Omnivorous natural enemies of herbivores consume plant-based resources and may elicit induced resistance in their host plant. A greater induction threshold for damage produced by omnivorous predators than for strict herbivores might be expected if omnivore performance is enhanced on noninduced plants, allowing them to reduce future levels of herbivory. Currently, it is not known if a plant responds to feeding by omnivorous predators and by herbivores similarly. To examine this question, we chose herbivore and omnivore species that produce the same kind of quantifiable damage to cotton leaves, enabling us to control statistically for the intensity of plant damage, and ask whether plant responses differed depending on the identity of the damaging species. We first compared changes in plant peroxidase activity, gossypol gland number and density, and leaf area in response to feeding by the spider mite Tetranychus turkestani (Ugarov and Nikolski) (an herbivore) and by one of the mite's principal natural enemies, the western flower thrips Frankliniella occidentalis (Pergande) (an omnivore). Both species increased the activity of peroxidase, but when we controlled for the amount of damage, the peroxidase activity of mite-damaged plants was higher than that of thrips-damaged plants. We also found that thrips, but not spider mites, increased the density of gossypol glands in the second true leaf. In a second experiment we included an additional herbivore, the bean thrips Caliothrips fasciatus (Pergande), to see if the different responses of cotton to thrips and mite herbivory we first observed were attributable to differences in trophic function (herbivore versus omnivore) or to other differences in feeding generated by thrips versus mites. Cotton plants exhibited the same pattern of induced responses (elevated peroxidase, increased number of glands, reduced leaf area) to herbivory generated by the bean thrips (an herbivore) and western flower thrips (an omnivore), suggesting that trophic function was not a key determinant of plant response. Thrips-damaged plants again showed a significantly higher density of gossypol glands than did mite-damaged plants. Overall, our results suggest that (1) an omnivorous predator systemically induces resistance traits in cotton and (2) whereas there is evidence of taxonomic specificity (thrips versus mites), there is little support for trophic specificity (herbivorous thrips versus omnivorous thrips) in the elicitation of induced responses.

Effect of Low and Very Low Doses of Simple Phenolics on Plant Peroxidase Activity

Changes in the activity of horseradish peroxidase resulting from an addition of ethanol water dilutions of 19 phenolic compounds were observed. For each compound, the enzyme activity was plotted against the degree of dilution expressed as n = -log(100) (mol/L) in the range 0 </= n >/= 20. All the curves showed sinusoidal activity, more or less regular, with two to four peaks on average. Each analyzed compound had a characteristic sinusoidal shape, which was constant for samples of peroxidase from various commercial firms. This was clearly visible after function fitting to experimental results based on the Marquadt-Levenberg algorithm using the least-squares method. Among the 19 phenolics, the highest amplitudes were observed for phenol and iso- and vanillate acids and aldehydes. The specific character of each of the analyzed curves offers a possibility of choosing proper dilutions of phenolic compound for activating or inhibiting of peroxidase activity.

Properties of guaiacol peroxidase activities isolated from corn root plasma membranes.

Although several investigations have demonstrated a plasma membrane (PM)-bound peroxidase activity in plants, this study is the first, to our knowledge, to purify and characterize the enzymes responsible. Proteins were extracted from highly enriched and thoroughly washed PMs. Washing and solubilization procedures indicated that the enzymes were tightly bound to the membrane. At least two distinct peroxidase activities could be separated by cation exchange chromatography (pmPOX1 and pmPOX2). Prosthetic groups were identified in fractions with peroxidase activity by absorption spectra, and the corresponding protein bands were identified by heme staining. The activities of the peroxidase enzymes responded different to various substrates and effectors and had different thermal stabilities and pH and temperature optima. Because the enzymes were localized at the PM and were not effected by p-chloromercuribenzoate, they were probably class III peroxidases. Additional size exclusion chromatography of pmPOX1 revealed a single activity peak with a molecular mass of 70 kD for the native enzyme, whereas pmPOX2 had two activity peaks (155 and 40 kD). Further analysis of these fractions by a modified sodium dodecyl sulfate-polyacrylamide gel electrophoresis in combination with heme staining confirmed the estimated molecular masses of the size exclusion chromatography.

POLIAMINAS E ATIVIDADE DA PEROXIDASE EM FEIJÃO (Phaseolus vulgaris L.) CULTIVADO SOB ESTRESSE SALINO

O teor de poliaminas (putrescina, espermidina e espermina) e a atividade enzimática da peroxidase (EC 1.11.1.7) foram determinados em plantas de Phaseolus vulgaris L. cv Carioquinha, após terem sido submetidas a estresse salino (50 e 100 mM de NaCl). Foram observadas alterações nos teores das poliaminas, principalmente putrescina, que aumentou com o tempo e a concentração de NaCl. Também ocorreu aumento na atividade da peroxidase em ambas concentrações de NaCl utilizadas. Os resultados mostraram alterações no metabolismo de poliaminas e peroxidases nas plantas de feijão cultivadas em meio salino.

The induction of soluble peroxidase activity in bean leaves by wind‐induced mechanical perturbation

The induction of defense-related peroxidase (POD) activity in plants occurs in response to many biotic and abiotic stimuli. This controlled greenhouse study was an attempt to provide insight into the nature of the induction of soluble POD activity by noninjurious wind-induced mechanical perturbation (MP). In a time course study, exposure of common bean (Phaseolus vulgaris) seedlings to daily periods of fan-produced wind induced a significant and sustained increase in soluble POD activity in primary leaves of 7-9-d-old seedlings. In a wind-gradient study, wind-induced MP led to increases in soluble POD activity in leaves that were proportionally related to the wind speed experienced by individual seedlings. Wind-induced MP enhanced soluble POD activity to a degree similar to treatment with 5 mmol/L HgCl(2), a potent oxidizing elicitor of POD activity in plants. However, no further increases in POD activity were induced by HgCl(2) on plants that were preconditioned with wind-induced MP. Finally, short periods of brushing-induced MP enhanced soluble POD activity to the same degree as longer periods of wind-induced MS, suggesting a greater sensitivity to thigmic stimuli than to seismic stimuli in leaves of bean seedlings. This study illustrates the potential importance of wind and other mechanical stimuli as inducers of POD activity and interacting factors in the elicitation of POD activity by other environmental stimuli.

Evidence for a primary role of active oxygen species in induction of host cell death during infection of bean leaves withBotrytis cinerea

Bean genotypes (Phaseolus vulgaris) selected for high or low sensitivity to oxidants showed similar stress responses to ozone, paraquat and to infection withBotrytis cinerea. The potentially oxidative nature of the fungal attack was investigated on bean leaf discs floated in diluted malt broth medium and inoculated with conidia ofB. cinereaisolates differing in aggressiveness. Hydrogen peroxide and OH* radicals were measuredin situduring infection. Additionally, peroxidases, cellulases, xylanases and polygalacturonases (PG) diffusing into the incubation medium during infection were analysed. An assay based on the oxidative degradation of 2-deoxyribose enabled the specific detection ofin situgenerated OH* radicals. The aggressiveness of six isolates ofBotrytiswas closely correlated with the amount of H2O2and OH* radicals detected in the leaf tissue during infection. Aggressive isolates induced peak signals of OH* radical formation within 24 h and strongly elevated levels of H2O2within 48 h post-inoculation (hpi), in a phase of most rapidly progressing infection. No such increases in active oxygen species (AOS) were detected in non-aggressive interactions. All fungal isolates tested suppressed plant peroxidase activity as compared to non-inoculated leaf discs. However, aggressive isolates were significantly more suppressive than non-aggressive ones, suggesting a role for peroxidases in plant resistance as scavengers of harmful AOS. Hydrogen peroxide production measured in infected leaf discs was stronger than its accumulation in the incubation medium, pointing to sources of H2O2inside the plant. The scavengers of AOS, catalase and D-mannitol significantly reduced severity of infection. Secretion of cellulases and xylanases occurred later than the start of infection, suggesting a role of these cell-wall degrading enzymes in the digestion of dead rather than the killing of living host tissue. PGs were produced by all fungal isolates much earlier (12 hpi) but the production did not reflect the isolate aggressiveness. This is the first study to directly detect toxic AOSin situduring infection of plant tissue byB. cinerea. It is concluded that AOS, besides their probable role in plant resistance, might be instrumental for necrotrophs likeB. cinereato kill the host tissue in initial stages of infection.