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The aim of this study was to investigate the bacterial communities on paclobutrazol [(2RS, 3RS)-1-(4-Chlorophenyl)-4, 4-dimethyl-2-(1H-1,2,4-triazol-1-yl) pentan-3-ol]-applied agricultural soils by denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR) amplified 16S rDNA gene fragments. Three different agricultural soil samples were collected from paclobutrazol applied mango and waxapple orchards, peanut fields and untreated rice fields as a control for DGGE analysis. The DGGE pattern of PCR- generated 16S rDNA gene fragments indicated that the bacterial populations from four paclobutrazol-applied soils of peanut fields were closely related to each other and two paclobutrazol-applied soils of mango and waxapple orchards harbored closely related bacterial communities. But, paclobutrazol-free agricultural soils comprised relatively a different bacterial group. However, the bacterial populations of mango and waxapple orchard are completely different from the bacterial communities of peanut field. Further purification and sequence analysis of 40 DGGE bands followed by phylogenetic tree assay showed similar results that soil bacteria from paclobutrazol applied mango and waxapple orchard are phylogenetically related. Based on the phylogenetic analysis, the clone M-4 was clad 100 % (bootstrap value) with Mycobacterium sp. The Mycobacterium sp. has been proved to degrade the phenolic compounds such as phenol, 4-chlorphenol, 2,4-dichlorophenol and paclobutrazol molecule containing chlorobenzene ring.

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Scientific evidences in the literature have shown that plants treated exogenously with micromole concentration of hydrogen peroxide (H(2)O(2)) acquire abiotic stress tolerance potential, without substantial disturbances in the endogenous H(2)O(2) pool. In this study, we enhanced the endogenous H(2)O(2) content of tobacco (Nicotiana tabaccum L. cv. SR1) plants by the constitutive expression of a glucose oxidase (GO; EC 1.1.3.4) gene of Aspergillus niger and studied their cold tolerance level. Stable integration and expression of GO gene in the transgenic (T(0)-T(2)) tobacco lines were ascertained by molecular and biochemical tests. Production of functionally competent GO in transgenic plants was confirmed by the elevated levels of H(2)O(2) in the transformed tissues. When three homozygous transgenic lines were exposed to different chilling temperatures for 12 h, the electrolyte conductivity was significantly lower in GO-expressing tobacco plants than the control plants; in particular, chilling protection was more prominent at -1 degree C. In addition, most transgenic lines recovered within a week when returned to normal culture conditions after -1 degree C-12 h cold stress. However, control plants displayed symptoms of chilling injuries such as necrosis of shoot tip, shoots and leaves, consequently plant death. The protective effect realized in the transgenic plants was comparable to cold-acclimatized wild tobacco. The chilling tolerance of transgenic lines was found associated, at least in part, with elevated levels of total antioxidant content, CAT and APX activities. Based on our findings, we predict that the transgenic expression of GO may be deployed to improve cold tolerance potential of higher plants.

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Two inhibitors, aviglycine and propargylglycine, were tested for their ability to suppress methionine synthesis thus inhibit conidial germination and mycelial growth of Czapek-Dox liquid medium grown Fusarium oxysporum f. sp. luffaemuM. The linear inhibition range for mycelial growth was about 7.6-762.9 microM. Although aviglycine did not completely inhibit both conidial germination and mycelial growth, it showed significant inhibitory effect at 1.5 microM. The inhibition range for propargylglycine against conidial germination and mycelial growth were from 0.08 to 8841 microM and from 0.8 to 884.1 microM, respectively. Propargylglycine inhibited conidial germination and mycelial growth at a concentration of 8841 muM. The EC(50) values of aviglycine were 1 microM for conidial growth and 122 microM for mycelial growth, and the EC(50) values of propargylglycine were 47.7 microM for conidial growth and 55.6 muM for mycelial growth. Supplement of methionine released inhibition of aviglycine or propargylglycine to conidial germination. In addition, a mixture of aviglycine (1.5 microM) and propargylglycine (8841 microM) showed additive inhibitive effect than applied alone on 10 isolates. From these results, both aviglycine and propargylglycine exhibited inhibitory activity, and suggest that they can provide potential tools to design novel fungicide against fungal pathogens.

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Transient oxidative shock induced by pretreatment of leaves with H2O2 effectively increased chilling tolerance in mung bean and Phalaenopsis. Seedlings of the chilling-tolerant (V3327) cultivar of mung bean (Vignaradiata L.) were employed to study the mechanism of H2O2-induced chilling tolerance. Pretreatment with 200 mM H2O2 increased survival rates of seedlings chilled at 4°C for 36 h from 30% to 70%. The same treatment also lowered the electrolyte leakage from 86% to 21%. Time-course analysis immediately after the treatment demonstrated that exogenous application of H2O2 did not alter the endogenous H2O2 level of the plants. This observation suggests that the primary receptor for the exogenous H2O2 is localized on the leaf surface or in some other way isolated from the endogenous H2O2 pool. Oxidative shock inhibited the induction of the antioxidant enzymes, ascorbate peroxidase and catalase; however, it substantially increased glutathione content both under chilling and control conditions. Combined pretreatment of mung bean plants with abscisic acid and H2O2 showed no synergistic effect on glutathione content and decreased survival rate relative to treatment with either compound alone. These results suggest that the H2O2-induced chilling tolerance in these plants might be mediated by an elevation of glutathione content and is independent of the ABA mechanism of chilling protection.

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Mung bean (Vigna radiata L. cv. TN5, a chilling-sensitive cultivar) was employed to evaluate the importance of glutathione in hydrogen peroxide (H2O2)-induced chilling tolerance. Seeds germinated at 25°C for 7d were subjected to different periods of chilling treatment, prior to analysis of the glutathione contents of their leaves. In a comparison of acclimation temperatures from 2-12°C, it was found that an 8°C acclimation for 36 h induced a 5.7-fold increase, the highest glutathione level among the temperatures tested. Seedlings acclimated at 8°C for 36 h showed 97% survival after a 36-h, 4°C chilling stress, compared with 33% survival of non-acclimated plants. Pretreatment with 200 mM H2O2 for 12 h before a 36-h, 4°C chilling treatment increased glutathione levels by 30% and reduced electrolyte leakage to 43%, relative to the untreated control. Treated seedlings also showed a survival rate of 71% after the same chilling treatment. Application of 1 mM buthionine sulfoximine, a specific inhibitor of glutathione synthesis, reversed the protection against chilling stress provided to seedlings either by acclimation at 8°C for 36 h or H2O2 pretreatment. The role of glutathione in chilling acclimation or H2O2-pretreatment-induced chilling tolerance is thus confirmed.