Functional imaging of plants: a nuclear magnetic resonance study of a cucumber plant. (49/376)

Functional magnetic resonance imaging was used to study transients of biophysical parameters in a cucumber plant in response to environmental changes. Detailed flow imaging experiments showed the location of xylem and phloem in the stem and the response of the following flow characteristics to the imposed environmental changes: the total amount of water, the amount of stationary and flowing water, the linear velocity of the flowing water, and the volume flow. The total measured volume flow through the plant stem was in good agreement with the independently measured water uptake by the roots. A separate analysis of the flow characteristics for two vascular bundles revealed that changes in volume flow of the xylem sap were accounted for by a change in linear-flow velocities in the xylem vessels. Multiple-spin echo experiments revealed two water fractions for different tissues in the plant stem; the spin-spin relaxation time of the larger fraction of parenchyma tissue in the center of the stem and the vascular tissue was down by 17% in the period after cooling the roots of the plant. This could point to an increased water permeability of the tonoplast membrane of the observed cells in this period of quick recovery from severe water loss.  (+info)

Purification of an aminopeptidase preferentially releasing N-terminal alanine from cucumber leaves and its identification as a plant aminopeptidase N. (50/376)

In this study, a highly active foliar aminopeptidase preferentially releasing N-terminal alanine from artificial substrates was purified and characterized from cucumber (Cucumis sativus L. suyo). The enzyme had a molecular mass of 200 kDa consisting of two subunits of 95 kDa. It was a metalloprotease the pH optimum of which was 8 to 9. It cleaved Ala-, Gly-, Met-, Ser-, Leu-, Lys-, and Arg artificial substrates. An internal amino acid sequence was similar to those of aminopeptidase N (clan MA, family M1) of microorganisms, and was very similar to that of a putative aminopeptidase N of Arabidopsis thaliana. From these results, the highly active aminopeptidase in cucumber leaves was identified to be a plant aminopepitdase N.  (+info)

Polyphenol increases in safflower and cucumber seedlings exposed to strong visible light with limited water. (51/376)

To assess effects of the environmental stress on polyphenol compounds (polyphenols) in plants, the polyphenol contents were investigated in the seedlings of safflower (Carthamus tinctrius L.) and cucumber (Cucumis sativus L.) grown under three types of growth conditions: control; light stress, irradiated with strong light in the visible wavelength range; and light/water stress, irradiated with strong visible light with a limited water supply. The total polyphenol contents and the amounts of the major polyphenols, especially luteolin 7-O-glucoside in safflower cotyledons, and luteolin 7-O-glucoside and luteolin in safflower foliage leaves, increased in response to both stresses. The polyphenol increasing effect of light/water stress was clearly observed in safflower compared to cucumber, suggesting that plants that are resistant to these stresses can accumulate substantial amounts of polyphenols compared to the plants which respond weakly to the stresses.  (+info)

Gibberellin produced in the cotyledon is required for cell division during tissue reunion in the cortex of cut cucumber and tomato hypocotyls. (52/376)

Cucumber (Cucumis sativus) hypocotyls were cut to one-half of their diameter transversely, and morphological and histochemical analyses of the process of tissue reunion in the cortex were performed. Cell division in the cortex commenced 3 d after cutting, and the cortex was nearly fully united within 7 d. 4',6-Diamidino-2-phenylindole staining and 5-bromo-2'-deoxyuridine labeling experiments indicate that nDNA synthesis occurred during this process. In addition, specific accumulation of pectic substances was observed in the cell wall of attached cells in the reunion region of the cortex. Cell division during tissue reunion was strongly inhibited when the cotyledon was removed. This inhibition was reversed by applying gibberellin (GA, 10(-4) M GA3) to the apical tip of the cotyledon-less plant. Supporting this observation, cell division in the cortex was inhibited by treatment of the cotyledon with 10(-4) M uniconazole-P (an inhibitor of GA biosynthesis), and this inhibition was also reversed by simultaneous application of GA. In contrast to the essential role of cotyledon, normal tissue reunion in cut hypocotyls was still observed when the shoot apex was removed. The requirement of GA for tissue reunion in cut hypocotyls was also evident in the GA-deficient gib-1 mutant of tomato (Lycopersicon esculentum). Our results suggest that GA, possibly produced in cotyledons, is essential for cell division in reuniting cortex of cut hypocotyls.  (+info)

Arbuscular mycorrhizal fungus-promoted accumulation of two new triterpenoids in cucumber roots. (53/376)

Cucumber (Cucumis sativus L.) roots were analyzed by HPLC and TLC for their levels of secondary metabolites upon inoculation with the arbuscular mycorrhizal fungus, Glomus caledonium. Three compounds in EtOAc extracts from the mycorrhizal roots showed significant increases six weeks after inoculation. These compounds were isolated by column chromatography and determined to be two novel triterpenes, 2beta-hydroxybryonolic acid (2beta,3beta-dihydroxy-D:C-friedoolean-8-en-29-oic acid) and 3beta-bryoferulic acid [3beta-O-trans-ferulyl-D:C-friedooleana-7,9(11)-diene-29-oic acid], and the known triterpene, bryonolic acid, by spectroscopic methods. Time-course experiments showed that the levels of the three terpenoids in cucumber roots were significantly increased by the application of a 53-microm sieving from a soil inoculum of the arbuscular mycorrhizal fungus containing soil microbes but no mycorrhizal fungi, and that mycorrhizal colonization further promoted the terpenoid accumulation. Inoculation with Glomus mosseae also enhanced the accumulation of the triterpenes, whereas no accumulation was observed by inoculating with the fungal pathogen, Fusarium oxysporum f. sp. cucumerinum. 2Beta-hydroxybryonolic acid was also isolated from the roots of melon and watermelon.  (+info)

Reaction of diphenyl diselenide with hydrogen peroxide and inhibition of delta-aminolevulinate dehydratase from rat liver and cucumber leaves. (54/376)

The interaction of the product of H2O2 and (PhSe)2 with delta-aminolevulinate dehydratase (delta-ALA-D) from mammals and plants was investigated. (PhSe)2 inhibited rat hepatic delta-ALA-D with an IC50 of 10 microM but not the enzyme from cucumber leaves. The reaction of (PhSe)2 with H2O2 for 1 h increased the inhibitory potency of the original compound and the IC50 for animal delta-ALA-D inhibition was decreased from 10 to 2 microM. Delta-ALA-D from cucumber leaves was also inhibited by the products of reaction of (PhSe)2 with H2O2 with an IC50 of 4 microM. The major product of reaction of (PhSe)2 with H2O2 was identified as seleninic acid and produced an intermediate with a (lambda)max at 265 nm after reaction with t-BuSH. These results suggest that the interaction of (PhSe)2 with mammal delta-ALA-D requires the presence of cysteinyl residues in close proximity. Two cysteine residues in spatial proximity have been recently described for the mammalian enzyme. Analysis of the primary structure of plant delta-ALA-D did not reveal an analogous site. In contrast to (PhSe)2, seleninic acid, as a result of the higher electrophilic nature of its selenium atom, may react with additional cysteinyl residue(s) in mammalian delta-ALA-D and also with cysteinyl residues from cucumber leaves located at a site distinct from that found at the B and A sites in mammals. Although the interaction of organochalcogens with H2O2 may have some antioxidant properties, the formation of seleninic acid as a product of this reaction may increase the toxicity of organic chalcogens such as (PhSe)2.  (+info)

Deleterious impact of a virulent bacteriophage on survival and biocontrol activity of Pseudomonas fluorescens strain CHAO in natural soil. (55/376)

Many biotic and abiotic factors affect the persistence and activity of beneficial pseudomonads introduced into soil to suppress plant diseases. One such factor may be the presence of virulent bacteriophages that decimate the population of the introduced bacteria, thereby reducing their beneficial effect. We have isolated a lytic bacteriophage (phi)GP100) that specifically infects the biocontrol bacterium Pseudomonas fluorescens CHA0 and some closely related Pseudomonas strains. phiGP100 was found to be a double-stranded-DNA phage with an icosahedral head, a stubby tail, and a genome size of approximately 50 kb. Replication of phiGP100 was negatively affected at temperatures higher than 25 degrees C. phiGP100 had a negative impact on the population size and the biocontrol activity of P. fluorescens strain CHA0-Rif (a rifampicin-resistant variant of CHA0) in natural soil microcosms. In the presence of phiGP100, the population size of strain CHA0-Rif in soil and on cucumber roots was reduced more than 100-fold. As a consequence, the bacterium's capacity to protect cucumber against a root disease caused by the pathogenic oomycete Pythium ultimum was entirely abolished. In contrast, the phage affected neither root colonization and nor the disease suppressive effect of a phiDGP100-resistant variant of strain CHA0-Rif. To our knowledge, this study is the first to illustrate the potential of phages to impair biocontrol performance of beneficial bacteria released into the natural soil environment.  (+info)

Analysis of minimal promoter sequences for plus-strand synthesis by the Cucumber necrosis virus RNA-dependent RNA polymerase. (56/376)

Tombusviruses are small, plus-sense, single-stranded RNA viruses of plants. A partially purified RNA-dependent RNA polymerase (RdRp) preparation of Cucumber necrosis virus (CNV), which is capable of de novo initiation of complementary RNA synthesis from either plus-strand or minus-strand templates, was used to dissect minimal promoter sequences for tombusviruses and their defective interfering (DI) RNAs. In vitro RdRp assay revealed that the core plus-strand initiation promoter included only the 3'-terminal 11 nucleotides. A hypothetical promoter-like sequence, which has been termed consensus sequence by Wu and White (1998, J. Virol. 72, 9897-9905), is recognized less efficiently by the CNV RdRp than the core plus-strand initiation promoter. The CNV RdRp can efficiently recognize the core plus-strand initiation promoter for a satellite RNA associated with the distantly related Turnip crinkle virus, while artificial AU- or GC-rich 3'-terminal sequences make poor templates in the in vitro assays. Comparison of the "strength" of minimal plus-strand and minus-strand initiation promoters reveals that the latter is almost twice as efficient in promoting complementary RNA synthesis. Template competition experiments, however, suggest that the minimal plus-strand initiation promoter makes an RNA template more competitive than the minimal minus-strand initiation promoter. Taken together, these results demonstrate that promoter recognition by the tombusvirus RdRp requires only short sequences present at the 3' end of templates.  (+info)