Activity In Cucumber Research Articles

Evaluation of Bacillus velezensis F9 for Cucumber Growth Promotion and Suppression of Fusarium wilt Disease.

Cucumber wilt, caused by Fusarium oxysporum f. sp. cucumerinum (FOC), is a soilborne disease that poses a significant threat to cucumber production, resulting in substantial yield losses. This study aimed to evaluate the biocontrol and growth-promoting effects of Bacillus velezensis, a highly active bacterial strain. In vitro assays revealed that B. velezensis F9 exhibited broad-spectrum antifungal activity against eight plant pathogenic fungi, with inhibition ratio ranging from 62.66% to 88.18%. Additionally, the strain displayed the ability to produce IAA (5.97 ± 1.75 µg/mL), fix nitrogen, produce siderophores, and form biofilms. In vitro growth promotion assays demonstrated that different concentrations of B. velezensis F9 significantly promoted cucumber seedling growth. Furthermore, two pot experiments revealed that the strain exhibited biocontrol efficacy against cucumber wilt, with disease control rates ranging from 42.86% to 67.78%. Notably, the strain significantly increased the plant height, fresh weight, and dry weight, with increases ranging from 20.67% to 60.04%, 40.27% to 75.51%, and 22.07% to 52.54%, respectively. Two field trials confirmed the efficacy of B. velezensis F9 in controlling cucumber wilt, with disease control rates of 44.95% and 33.99%, respectively. The strain effectively alleviated the dwarfing and wilting symptoms caused by the pathogen. Compared with the FOC treatment, the F9 + FOC treatment significantly increased the plant height, fresh weight, and dry weight, with increases of 43.85% and 56.28%, 49.49% and 23.70%, and 36.25% and 73.63%, respectively. Enzyme activity assays indicated that inoculation significantly increased SOD activity in cucumber leaves and neutral phosphatase, sucrase, and urease activity in rhizosphere soil. Correlation analysis revealed a negative correlation between the disease index and plant height, fresh weight, dry weight, and peroxidase activity, with correlation coefficients of -0.53, -0.60, -0.38, and -0.45, respectively. These findings suggest that plant height, fresh weight, and dry weight are significantly negatively correlated with the cucumber disease index, highlighting their importance as indicators for evaluating the biocontrol efficacy of B. velezensis F9. In conclusion, B. velezensis F9 is a highly effective plant growth-promoting rhizobacterium with excellent biocontrol potential, showcasing promising applications in agricultural production.

Role of root plasma membrane H+-ATPase in enhancing Cucumis sativus adaptation to microcystins.

Microcystins (MCs) are the most widespread and hazardous cyanotoxins posing a huge threat to agro-ecosystem by irrigation. Some adaptive metabolisms can be initiated at the cellular and molecular levels of plant to survive environmental change. To find ways to improve plant tolerance to MCs after recognizing adaptive mechanism in plant, we studied effects of MCs on root morphology, mineral element contents, root activity, H+-ATPase activity, and its gene expression level in cucumber during exposure and recovery (without MCs) periods. After being exposed to MCs (1, 10, 100 and 1000μg L-1) for 7days, we found 1μg L-1 MCs did not affect growth and mineral elements in cucumber. MCs at 10μg ·L-1 increased root activity and H+-ATPase activity partly from upregulation of genes (CsHA2, CsHA3, CsHA8, and CsHA9) expression, to promote nutrient uptake. Then, the increase in NO3-, Fe, Zn, and Mn contents could contribute to maintaining root growth and morphology. Higher concentration MCs (100 or 1000µg L-1) inhibited root activity and H+-ATPase activity by downregulating expression of genes (CsHA2, CsHA3, CsHA4, CsHA8, CsHA9, and CsHA10), decreased contents of nutrient elements except Ca largely, and caused root growing worse. After a recovery, the absorption activity and H+-ATPase activity in cucumber treated with10 μg L-1 MCs were closed to the control whereas all parameters in cucumber treated 1000μg L-1 MCs were even worse. All results indicate that the increase in H+-ATPase activity can enhance cucumber tolerance to MC stress by regulating nutrient uptake, especially when the MCs occur at low concentrations.

Enhancement of phenylalanine ammonia-lyase activity in cucumber and chilli seedlings by aqueous extract of Cleistanthus collinus

Enhancement of phenylalanine ammonia-lyase activity in cucumber and chilli seedlings by aqueous extract of Cleistanthus collinus

Spermidine Modify Antioxidant Activity in Cucumber Exposed to Salinity Stress

The effects of short-term 48 h long NaCl-stress and spermidine level modification on polyamines level and antioxidant status in cucumber (Cucumis sativus cv. Dar) leaves were investigated. Seedlings kept in nutrient solutions treated with 50 mM NaCl for 48 h exhibited reduced relative water content and accumulation of free polyamines, especially spermidine. Salinity stress caused an increase in superoxide radicals and hydrogen peroxide generation during the salinity-induced increase in antioxidant enzyme activities. Spermidine application before stress resulted in a marked increase in spermidine and spermine contents in the leaves of salt-stressed cucumber seedlings. Additionally, increased spermidine/spermine level mobilised the antioxidant enzyme’s activity and limited reactive oxygen species content. Polyamine synthesis inhibitor (MGBG) slightly decreased spermidine and spermine levels during salinity and reversed the antioxidant activity mobilisation. These results showed that Spd modifications significantly improved PAs, enhancing salinity stress tolerance by detoxifying ROS. Our findings determined the implication of PAs for improving the salinity tolerance of important vegetable species.

Application of Various Extracts Enhances the Growth and Yield of Cucumber (Cucumis sativus L.) without Compromising the Biochemical Content

This study examined the effects of changes to application methods, application time, and combinations of different extracts on the growth and yield of cucumbers. Chlorophyll and photosynthetic efficiency levels in cucumber plants were also measured after receiving treatments of selected liquid fertilizers. Mineral nutrition levels in both extracts themselves and the test plants were measured. Crude protein, crude fat, ash, total phenol and flavonoid contents, and DPPH radical scavenging activity in cucumber were determined. Cucumber plant height and shoot fresh weight at 7 and 14 days after treatments generally increased significantly regardless of the extraction methods or extract materials. On the other hand, cucumber leaf number was similar regardless of the extracts used. The application frequency effects differed according to the extraction methods, extracts, and parameters investigated. In addition, the combinations of extracts did not produce significant increases in cucumber plant growth. Cucumber fruit weight was 17–81%, 10–61%, and 10–45% higher than the control or oil cake when the plants were treated with fermentation, boiled water, and water extracts, respectively. The chlorophyll content and photosynthetic efficiency of cucumber plants treated with various extracts did not vary significantly. Extracts with the highest mineral nutrients were not effective growth promotors of cucumber plants. This means that growth promotion may not be caused by high levels of one specific macro or micro element but by some specific combinations of various elements. Compared to the control, most elements in the cucumber leaves decreased significantly when treated with most of the extracts. Generally, crude protein, crude fat, and ash contents were not negatively affected by the extract treatments. Moreover, most of the extracts did not adversely affect total phenol and flavonoid contents and DPPH radical scavenging activity. Thus, these extracts may be used for growth promotion without negative effects to primary and secondary substances in organically cultivated crop fields.

Local and Systemic Changes in Photosynthetic Parameters and Antioxidant Activity in Cucumber Challenged with Pseudomonas syringae pv lachrymans.

We studied changes in gas exchange, photochemical activity and the antioxidant system in cucumber leaves locally infected with Pseudomonas syringae pv lachrymans and in uninfected systemic ones. Infection-induced declined net photosynthesis rate and the related changes in transpiration rate, the intracellular CO2 concentration, and prolonged reduction in maximal PSII quantum yield (Fv/Fm), accompanied by an increase in non-photochemical quenching (NPQ), were observed only in the infected leaves, along with full disease symptom development. Infection severely affected the ROS/redox homeostasis at the cellular level and in chloroplasts. Superoxide dismutase, ascorbate, and tocopherol were preferentially induced at the early stage of pathogenesis, whereas catalase, glutathione, and the ascorbate–glutathione cycle enzymes were activated later. Systemic leaves retained their net photosynthesis rate and the changes in the antioxidant system were partly like those in the infected leaves, although they occurred later and were less intense. Re-balancing of ascorbate and glutathione in systemic leaves generated a specific redox signature in chloroplasts. We suggest that it could be a regulatory element playing a role in integrating photosynthesis and redox regulation of stress, aimed at increasing the defense capacity and maintaining the growth of the infected plant.

Biostimulant Potential of Scenedesmus obliquus Grown in Brewery Wastewater.

Microalgae are microorganisms with the capacity to contribute to the sustainable and healthy food production, in addition to wastewater treatment. The subject of this work was to determine the potential of Scenedesmus obliquus microalga grown in brewery wastewater to act as a plant biostimulant. The germination index of watercress seeds, as well as the auxin-like activity in mung bean and cucumber, and in the cytokinin-like activity in cucumber bioassays were used to evaluate the biostimulant potential. Several biomass processes were studied, such as centrifugation, ultrasonication and enzymatic hydrolysis, as well as the final concentration of microalgal extracts to determine their influence in the biostimulant activity of the Scenedesmus biomass. The results showed an increase of 40% on the germination index when using the biomass at 0.1 g/L, without any pre-treatment. For auxin-like activity, the best results (up to 60% with respect to control) were obtained at 0.5 g/L of biomass extract, after a combination of cell disruption, enzymatic hydrolysis and centrifugation. For cytokinin-like activity, the best results (up to 187.5% with respect to control) were achieved without cell disruption, after enzymatic hydrolysis and centrifugation at a biomass extract concentration of 2 g/L.

Effects of low irradiation on photosynthesis and antioxidant enzyme activities in cucumber during ripening stage

In order to investigate the effects of low irradiation (LI) on cucumber (Cucumis sativus L. cv. Jinyou 35) during a ripening stage, our experiment was carried out in a climate chamber. Two levels of PAR were set for plants: normal irradiation [NI, 600 μmol(photon) m−2 s−1] and low irradiation [LI, 100 μmol(photon) m−2 s−1], respectively. The experiments lasted for 9 d; then both groups of plants were transferred under NI to recover for 16 d. The plants showed severe chlorosis after the LI treatment. Chlorophyll (Chl) a, initial slope, photosynthetic rate at saturating irradiation (P max), light saturation point, maximal photochemical efficiency of PSII (Fv/Fm), electron transport rate of PSII (ETR), soluble protein content, and catalase (CAT) activity in cucumber leaves decreased under LI stress, while Chl b, carotenoids, light compensation point, nonphotochemical quenching (qN), superoxide dismutase (SOD), and malondialdehyde (MDA) exhibited an increasing trend under LI. After 16 d of recovery, values of P max, Fv/Fm, ETR, qN, SOD, CAT, MDA, and soluble protein were close to those of the control after one, three, and five days of the LI treatment, while those kept under LI for 7 and 9 d could not return to the control level. Therefore, 7 d of LI stress was a meteorological disaster index for LI in cucumber at the fruit stage.

Nitrate reductase activity and yield of dry mass and protein content in cucumber seedlings supplied with nitrates and ammonium

The presence of NH<sub>4</sub><sup>+</sup> ions in a nutrient solution containing NH<sub>4</sub>NO<sub>3</sub> with the K+ ions removed, caused an inhibition of nitrate reductase (NR) activity in cucumber leaves. The lack of K<sup>+</sup> in a NaNO<sub>3</sub> medium also decreased the NR activity. Addition of K<sup>+</sup> to these media suppressed the inhibitory effect of NH<sub>4</sub><sup>+</sup> and enhanced the NR activity in the leaves of plants growing in NaNO<sub>3</sub> nutrient solution. The results suggest that K<sup>+</sup> is essential for NO<sub>3</sub><sup>-</sup> reduction, Na<sup>+</sup> is less effective in this process, whereas NH<sub>4</sub><sup>+</sup> ions markedly inhibit NO<sub>3</sub><sup>-</sup> reduction. The protein content and increment of dry mass of cucumber plants grown 10 days with NH<sub>4</sub>-N as the sole source of nitrogen was significantly lower as compared with NO<sub>3</sub>-N supplied plants feed with plants feed with both forms of mineral nitrogen (NH<sub>4</sub>NO<sub>3</sub>). The results show that cucumber prefers the nitrates, although it can utilize the ammonium form of nitrogen.

Combined effects of salt stress and cucurbit downy mildew (Pseudoperospora cubensis Berk. and Curt. Rostov.) infection on growth, physiological traits and antioxidant activity in cucumber (Cucumis sativus L.) seedlings

Abiotic and biotic stresses both decrease quality and quantity of cultivated plants. We compared responses of Cucumis sativus L. cvs Sardes and Beith alpha which were treated with 50 or 100 mM NaCl and/or infected by Pseudoperospora cubensis Berk. and Curt. Rostov.. Both cultivars were affected remarkably when fungus infection was combined with salt stress however; cv Sardes was found out to be relatively tolerant with sustainable growth performance, better leaf water status and lower lipid peroxidation levels under this condition. This relative tolerance could be related to the fine tuning of the activities of the antioxidative enzymes and proline levels.

Different effect of cadmium and copper on H+-ATPase activity in plasma membrane vesicles from Cucumis sativus roots

The effect of heavy metals on plasma membrane (PM) H+-ATPase (EC 3.6.3.14) activity in cucumber (Cucumis sativus) roots was studied. The aim of this work was to explain the mechanism of modification of the PM H+-ATPase activity in plants subjected to heavy metals. Plants were treated with 10 μM Cd or Cu for 6 d. After 3 d exposure to the heavy metals, some of the plants were transferred to control conditions for a further 3 d (3/3 plants). The activity of PM H+-ATPase was found to be increased in plants treated with heavy metals. The highest activity measured as proton transport was observed in 3/3 plants. Estimation of transcript levels of C. sativus PM H+-ATPase in roots indicated that the action of Cd, but not Cu, affected the gene expression level. Transcript levels of C. sativus PM H+-ATPase (CsHA2, CsHA3, CsHA4, CsHA8, and CsHA9) genes increased in roots treated with Cd. Moreover, Western blot analysis with antibody against phosphothreonine and 14-3-3 protein indicated that increased activity of PM H+-ATPase under heavy-metal stress resulted from phosphorylation of the enzyme. It was found that Cu markedly increased the activity of catalase and ascorbate peroxidase and reduced the level of H2O2 in cucumber roots. In contrast, Cd did not affect these parameters. These results indicate that Cd and Cu can, in different ways, lead to modification of PM H+-ATPase activity. Additionally, it was observed that treatment of plants with heavy metals led to an increased level of heat-shock proteins in the tissues. This suggests that the plants had started adaptive processes to survive adverse conditions, and increased PM H+-ATPase activity could further enhance the repair processes in heavy-metal-stressed plants.

Fertilizer properties of DCHA/Fe3+

The suitability of the non-symmetrical chelating agent DCHA (2-{2-[(2-hydroxybenzyl)amino]ethylamino}-2-{2-hydroxyphenyl}acetic) to improve Fe nutrition in plants is investigated in order to confirm the good results deriving from its chemical reactivity in agronomic systems achieved by analytical and modeling studies. Moreover, the factors affecting the efficacy of this new Fe chelate, that it is predicted to combine a good stability in nutrient solution and calcareous soils, are explored. The role of DCHA/Fe3+ as substrate for the Fe chelate reductase (FCR) activity in cucumber (Cucumis sativus L. cv. Ashley) plants and its efficacy to provide Fe to chlorotic soybean (Glycine max L. cv. Stine 0408) plants in both hydroponic and soil culture were determined. The chelate DCHA/Fe3+ presented an intermediate behavior between o,oEDDHA/Fe3+ and o,pEDDHA/Fe3+ as substrate of the FCR. In the hydroponic experiment, nutritional indexes indicated a faster and higher re-greening of the plants treated with DCHA/Fe3+ and o,pEDDHA/Fe3+ than with o,oEDDHA/Fe3+. In the soil experiment, plants treated with o,oEDDHA/57Fe3+ showed the highest 57Fe concentration in leaves and no differences were observed between o,pEDDHA/57Fe3+ and DCHA/57Fe3+. The chelate DCHA/Fe3+ has adequate fertilizer properties since it is able to correct the Fe chlorosis and to maintain good nutritional status of plants over time both in hydroponic and soil cultures. This is related to its ability to serve as substrate for the FCR and its good stability in solution and in soil conditions observed in this and previous studies.

Cloning of the gene encoding cucumber lumazine synthase and an analysis of its promoter activity in cucumber

Promoters are an important regulatory element controlling the temporal and spatial expression of genes; thus, they play a critical role in genetic engineering by controlling target gene expression. Cucumber is a widely planted vegetable with a pleasant flavor and high economic value. However, most genetic engineering studies involving cucumber have utilized the CaMV 35S promoter, which mediates ubiquitous target gene expression. To identify a promoter that is highly expressed in cucumber fruit, total proteins from cucumber fruit were analyzed by two-dimensional gel electrophoresis. One spot which is highly expressed in fruit was sequenced from its N-terminus using the Edman degradation method. A total of 10 amino acids (Ala-Val-Arg-His-Ile-Ala-Gly-Ser-Leu-Ala) were sequenced. Based on these 10 residues, a cDNA fragment 905 bp in length was cloned using 3′- and 5′-RACE. The corresponding gene, which encodes 220 amino acids, showed 65-73% similarity to other plant lumazine synthases without the signal peptide. We also cloned the 2.1-kb upstream promoter sequence of this Cucumis sativus lumazine synthase (CsLS) and analyzed its promoter activity by GUS histochemical and fluorometric assays. Our results indicate that CsLS is highly expressed in cucumber fruit, whereas it is expressed at low levels in cucumber stems and leaves.

Exogenous Hydrogen Peroxide Changes Antioxidant Enzyme Activity and Protects Ultrastructure in Leaves of Two Cucumber Ecotypes Under Osmotic Stress

Cucumber (Cucumis sativus L.) varieties cv. Jinchun no. 4 (a North China ecotype) and cv. Lvfeng no. 6 (a South China ecotype) were cultivated to explore the effects of osmotic stress on the ultrastructure of chloroplasts and mitochondria, as well as to assess the possible protective effect of exogenous hydrogen peroxide (H2O2). Under osmotic stress induced by 10% polyethylene glycol 6000, 84.3% of the chloroplasts in Jinchun no. 4 were abnormal, whereas 88.6% were abnormal in Lvfeng no. 6. Abnormal mitochondria occurred in these two strains at rates of 78.5 and 87.1%, respectively. The stress condition disintegrated the membranes of most chloroplasts and mitochondria in the leaf cells of both cucumber ecotypes, and it also increased the malondialdehyde (MDA) content. We subjected the two cultivars to a combined treatment with H2O2 and osmotic stress and made the following observations: (1) Abnormal chloroplasts occurred at rates of 25.7 and 28.6%, and abnormal mitochondria were observed at rates of 22.9 and 32.8%, respectively. (2) Most of the investigated membranes were well organized in leaves of Jinchun no. 4 and Lvfeng no. 6, and the levels of endogenous H2O2, superoxide anion, and MDA were lower. Osmotic stress and exogenous H2O2 both increased the activities of antioxidative enzymes such as manganese superoxide dismutase, glutathione peroxidase, catalase, guaiacol peroxidase, ascorbate peroxidase, glutathione reductase, monodehydroascorbate reductase, dehydroascorbate reductase, and the antioxidants ascorbate and reduced glutathione. The combined effect of osmotic stress and exogenous H2O2 resulted in the highest antioxidant activities in both cucumber ecotypes. We propose that exogenous H2O2 increases antioxidant activity in cucumber leaves and thereby decreases lipid peroxidation to some extent, thus protecting the ultrastructure of most chloroplasts and mitochondria under osmotic stress.

Protective role of proline against salt stress is partially related to the improvement of water status and peroxidase enzyme activity in cucumber

A salt-sensitive cucumber cultivar “Jinchun No. 2” (Cucumis sativus L.) was used to investigate the role of proline in alleviating salt stress in cucumber. Proline was applied twice (day 0 and day 4 after salt treatment) as a foliar spray, with a volume of 25 mL per plant at each time. Plant dry weight, leaf relative water content, proline, malondialdehyde (MDA), Na+, K+ and Cl− contents, as well as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) activities in the plants were determined at day 8 after salt treatment. The results showed that 100 mmol L–1 NaCl stress significantly decreased plant dry weight, leaf relative water and K+ contents, and increased leaf MDA, Na+ and Cl− contents and SOD, POD, CAT and APX activities. However, leaf proline accumulation was not affected by salinity. The exogenous application of proline significantly alleviated the growth inhibition of plants induced by NaCl, and was accompanied by higher leaf relative water content and POD activity, higher proline and Cl− contents, and lower MDA content and SOD activity. However, there was no significant difference in Na+ and K+ contents or in CAT and APX activities between proline-treated and untreated plants under salt stress. Taken together, these results suggested that the foliar application of proline was an effective way to improve the salt tolerance of cucumber. The enhanced salt tolerance could be partially attributed to the improved water status and peroxidase enzyme activity in the leaf.

Biological Mode of Action of Dimethomorph on Pseudoperonospora cubensis and Its Systemic Activity in Cucumber

Dimethomorph is a fungicide with high activity against Peronosporomycetes plant pathogens. The present study showed that dimethomorph is effective on controlling the oomycete fungal pathogen Pseudoperonospora cubensis causing downy mildew on cucumber. The fungicide did not affect zoospores discharge from sporangia of P. cubensis, but it strongly inhibited mycelial growth and sporangial production in vitro and increased lysis of zoospores. Dose of 2 mg L −1 of dimethomorph was sufficient to inhibit mycelial growth and sporangial production of P. cubensis on leaf disks, 5 mg L −1 was enough to lyse zoospores of P. cubensis, and 25 mg L −1 was required to inhibit sporangial production on detached leaves. In whole plant tests, dimethomorph exhibited strong protective and curative activity. Dimethomorph when applied at a dose of 300 mg L −1 for 1, 3, 5, 7 days before inoculation exhibited 100% efficacy on disease control. On the other hand, efficacies of 67.1 and 31.5% were obtained when the same dose of dimethomorph was applied for 1 and 3 days after inoculation, respectively. So dimethomorph had persistence effect on leaves for 7 days at least and exhibited strong protective and curative activity. Bioassay analyses showed that dimethomorph could be translocated in the xylem system, redistributed in the leaf, and penetrated from the upper surface to the lower surface of the leaf but could not be translocated in phloem system or transferred from the roots to leaves of cucumber plants in sufficient amounts for disease control. The biocharacteristics of dimethomorph make it well suitable for integration of a control programme against downy mildew disease on cucumber and as a component to delay other peronosporomycetes fungicide-resistance development.

A novel bi-directional promoter cloned from melon and its activity in cucumber and tobacco

A bi-directional promoter, DP, was cloned by PCR amplification using the genomic DNA of melon as template. Analysis of itscis-acting elements in both directions revealed a series of inducible regulatory elements and some enhancer elements. To evaluate its transcriptional activity, DP in both directions was then cloned into vector pBI121 to replace the CaMV 35S promoter. DP in both directions also was inserted downstream of CaMV 35S to investigate whether the double promoter might affect expression of theuidA reporter gene at higher levels. Transient expression in cucumber leaves, stems, and fruits as well as in tobacco leaves and stems showed that DP in both directions drove transcription to much higher levels than did the single promoter CaMV 35S. However, activity of the double promoter was lower than the corresponding activity of the single promoter DP in both directions. These results demonstrate that DP is a natural bi-directional promoter, with much more activity than is found with the CaMV 35S promoter. Furthermore, in cucumber and tobacco, it is not suitable to insert DP in either direction downstream of the CaMV 35S promoter to form a double promoter.

The effect of benzothiadiazole and fungal extracts of Cercospora beticola and Fusarium graminearum on phosphoenolpyruvate carboxylase activity in cucumber leaves

The cytosolic phosphoenolpyruvate carboxylase (PEPC) catalyses the anaplerotic synthesis of oxalacetic acid resulting in the replenishment of citric acid cycle intermediates, which are precursors for the synthesis of amino acids. Biotic stress in plants generally leads to redistributions in primary and secondary pathways and therefore to a shift in the requirement of proteins. To reveal whether and how PEPC is affected by biotic stress we analysed PEPC activity after treating cucumber (Cucumis sativus) leaves with the synthetic plant activator benzothiadiazole (BTH) and extracts of the economically important phytopathogenic fungi Cercospora beticola and Fusarium graminearum. BTH as well as fungal extracts increased PEPC activity significantly 72 and 96 hours after treatments. In addition, the extracts, but not BTH, induced the formation of necrotic lesions. Defence responses are generally associated with decreased photosynthesis rates, an enhanced respiration rate and an increased demand in proteins. Regarding our results we assume that the increase in PEPC activity by biotic stress is conducive to a compensation of these antagonistic processes. However, PEPC activity enhancements are not necessarily associated with the formation of necrotic lesions. This study indicates that PEPC is involved in biotic stress responses and we suggest that PEPC contributes to successful defence responses in plants.

Stress induced plant resistance and enzyme activity varying in cucumber

When pathogens penetrate plant cells, some chemical secretions are elicited, and the mechanical signals in plant cell may be induced by the simultaneous physical pressure to change. Based on the previous cognitions, we investigated the plant resistance and the variation of anti-disease enzyme activity in cucumber leaves after mechanical stress loading. Results showed that the appropriate mechanical stimulation could significantly improve plant resistance and alter the activity of phenylalanine ammonial lyases (PAL) and POD, leading to synthesis of lignin. However, we found that the effects of the stress on these cellular fundamental events were eliminated when the adhesion between plasma membrane and cell wall was disrupted. We speculated that mechanical signal transduction in plants depend on the adhesion of plasma membrane–cell wall.

Effects of metal elements on acid phosphatase activity in cucumber ( Cucumis sativus L.) seedlings

Acid phosphatases (E.C.3.1.3.2) are a group of enzymes widely distributed in nature, which nonspecifically catalyze the hydrolysis of a variety of phosphate esters in pH ranges from 4 to 6 and play a major role in the supply and metabolism of phosphate in plants. The objective of the present study was to investigate the in vitro effects of some metals on the activity of acid phosphatase in cucumber seedlings ( Cucumis sativus L.) and to determine their kinetic parameters. The enzyme was assayed with Hg, Cd, Mn, Pb, Zn, K and Na at the 0.001–1 mM range using ATP, PPi and β-glycerol phosphate as substrates. Mn, Na and Cd did not significantly alter the enzyme activity. K caused a broad activation at low concentrations and an inhibition at high concentrations (10 mM) and lead caused no inhibition. Acid phosphatase was inhibited by Hg and Zn and the inhibition type and IC 50 values were determined for these metals. Hg presented a mixed inhibition type with PPi and ATP as substrates and uncompetitive inhibition with β-glycerol phosphate as substrate. Zn presented competitive inhibition for ATP as substrate, and a mixed inhibition type with PPi and β-glycerol phosphate as substrate. IC 50 values were 0.02, 0.3 and 0.15 mM for Hg, and 0.056, 0.035 and 0.24 mM for Zn with ATP, PPi and β-glycerol phosphate as substrates, respectively. Analysis of these results indicates that Zn is a more potent inhibitor of acid phosphatase from cucumbers than Hg.