A trans-zeatin riboside in root xylem sap negatively regulates adventitious root formation on cucumber hypocotyls.
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Shoot cultures of cucumber were used to analyse the roles of root-derived substances in adventitious root formation on hypocotyl tissues. Xylem sap collected from the roots of squash had a strong inhibitory effect on the formation of hypocotyl adventitious roots. Double-solvent extraction followed by fractionation with both normal and reverse phase column chromatographies and analysis by liquid chromatography/tandem mass spectrometry identified trans-zeatin riboside (ZR) as the primary suppressor of adventitious root formation. ZR was the predominant cytokinin present in the xylem sap, occurring at a concentration of 2x10(-8 )M. Application of ZR at concentrations from 3.16x10(-9) M effected inhibition of adventitious root formation. These results suggest that ZR transported from roots via xylem sap may act as an endogenous suppressor of hypocotyl adventitious root formation in planta. (+info)
Chilling root temperature causes rapid ultrastructural changes in cortical cells of cucumber (Cucumis sativus L.) root tips.
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Examination of root tips from cucumber (Cucumis sativus L.) seedlings grown at 8 degrees C for varying periods ranging from 15 min to 96 h, showed marked changes in the ultrastructure of cortical cells within only 15 min of exposure. Greater parts of the cortex were affected with longer periods of exposure, but the sequence of morphological changes in cell components was similar to that found for the roots exposed for 15 min. The effect of chilling injury included alterations in cell walls, nuclei, ER, mitochondria, plastids, and ribosomes. The extent of alterations varied greatly among cells, moderate to severe alterations to cell components being observable among adjoining cells. The measurements of root pressure using the root pressure probe showed a sudden, steep drop in the root pressure in response to lowering of the temperature of the bathing solution from 25 degrees C to 8 degrees C. These observations are discussed in the light of the information available on the ultrastructural and biochemical characteristics of the effect of cold exposure in chilling-sensitive plants. (+info)
The mitogen-activated protein kinase gene MAF1 is essential for the early differentiation phase of appressorium formation in Colletotrichum lagenarium.
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Colletotrichum lagenarium, the causal agent of cucumber anthracnose, invades host plants by forming a specialized infection structure called an appressorium. In this fungus, the mitogen-activated protein kinase (MAPK) gene CMK1 is involved in several steps of the infection process, including appressorium formation. In this study, the goal was to investigate roles of other MAPKs in C. lagenarium. The MAPK gene MAF1, related to Saccharomyces cerevisiae MPK1 and Magnaporthe grisea MPS1, was isolated and functionally characterized. The maf1 gene replacement mutants grew normally, but there was a significant reduction in conidiation and fungal pathogenicity. The M. grisea mps1 mutant forms appressoria, but conidia of the C. lagenarium maf1 mutants produced elongated germ tubes without appressoria on both host plant and glass, on which the wild type forms appressoria, suggesting that MAF1 has an essential role in appressorium formation on inductive surfaces. On a nutrient agar, wild-type conidia produced elongated germ tubes without appressoria. The morphological phenotype of the wild type on the nutrient agar was similar to that of the maf1 mutants on inductive surfaces, suggesting repression of the MAF1-mediated appressorium differentiation on the nutrient agar. The cmk1 mutants failed to form normal appressoria but produced swollen, appressorium-like structures on inductive surfaces, which is morphologically different from the maf1 mutants. These findings suggest that MAF1 is required for the early differentiation phase of appressorium formation, whereas CMK1 is involved in the maturation of appressoria. (+info)
Synthesis and insecticidal activity of N-oxydihydropyrroles: 4-hydroxy-3-mesityl-5,5-dimethyl derivatives with various substituents at the 1-position.
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A new series of N-oxydihydropyrrole derivatives was synthesized and evaluated for insecticidal activity against Nilaparvata lugens and Myzus persicae. Various substituents were introduced to the 1-position of the dihydropyrrole ring, and the derivatives obtained exhibited systemic and/or contact insecticidal activity. The structure-activity relationship revealed that small alkyoxy and alkoxyalkoxy groups were more favorable than alkylcarbonyloxy, alkoxycarbonyloxy, or sulfonyloxy groups as substituents at the 1-position. (+info)
RNA recombination between cucumoviruses: possible role of predicted stem-loop structures and an internal subgenomic promoter-like motif.
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We previously analyzed hybrids of Cucumber mosaic virus (CMV) and Tomato aspermy virus (TAV) that contained CMV RNA2 with the 3'-terminal sequence from TAV RNA2. In this article, we scrutinized the RNA3 molecules in these hybrid viruses by Northern hybridization and RT-PCR and found some recombinant CMV RNA3 molecules and various recombinant RNA4 molecules whose 3'-termini were derived from TAV RNA1 or 2. Sequence analyses revealed that most of the crossover sites for recombination were located near putative stem-loop structures and an internal subgenomic promoter-like motif. We inoculated in vitro transcripts synthesized from cDNA clones of the recombinant RNA3 onto N. benthamiana along with either CMV RNA1 and 2 or TAV RNA1 and 2. Although all of the hybrids were infectious, many sequence deletions and nucleotide substitutions were found when RNA1 and 2 from TAV were used, which suggests that fidelity of TAV replicase was lower than that of CMV replicase. The possible role of secondary structures and an internal subgenomic promoter-like motif in RNA recombination is discussed. (+info)
Evidence that binding of cucumber necrosis virus to vector zoospores involves recognition of oligosaccharides.
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Despite the importance of vectors in natural dissemination of plant viruses, relatively little is known about the molecular features of viruses and vectors that permit their interaction in nature. Cucumber necrosis virus (CNV) is a small spherical virus whose transmission in nature is facilitated by zoospores of the fungus Olpidium bornovanus. Previous studies have shown that specific regions of the CNV capsid are involved in transmission and that transmission defects in several CNV transmission mutants are due to inefficient attachment of virions to the zoospore surface. In this study, we have undertaken to determine if zoospores contain specific receptors for CNV. We show that in vitro binding of CNV to zoospores is saturable and that vector zoospores bind CNV more efficiently than nonvector zoospores. Further studies show that treatment of zoospores with periodate and trypsin reduces CNV binding, suggesting the involvement of glycoproteins in zoospore attachment. In virus overlay assays, CNV binds to several proteins, whereas CNV transmission mutants either fail to bind or bind at significantly reduced levels. The possible involvement of specific sugars in attachment was investigated by incubating CNV with zoospores in the presence of various sugars. Two mannose derivatives (methyl alpha-D-mannopyranoside and D-mannosamine), as well as three mannose-containing oligosaccharides (mannotriose, alpha3,alpha6-mannopentaose, and yeast mannan) and L-(-)-fucose, all inhibited CNV binding at relatively low concentrations. Taken together, our studies suggest that binding of CNV to zoospores is mediated by specific mannose and/or fucose-containing oligosaccharides. This is the first time sugars have been implicated in transmission of a plant virus. (+info)
CsAGP1, a gibberellin-responsive gene from cucumber hypocotyls, encodes a classical arabinogalactan protein and is involved in stem elongation.
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Fluorescence differential display was used to isolate the gibberellin (GA)-responsive gene, CsAGP1, from cucumber (Cucumis sativus) hypocotyls. A sequence analysis of CsAGP1 indicated that the gene putatively encodes a "classical" arabinogalactan protein (AGP) in cucumber. Transgenic tobacco (Nicotiana tabacum) plants overexpressing CsAGP1 under the control of the cauliflower mosaic virus 35S promoter produced a Y(betaGlc)(3)-reactive proteoglycan in addition to AGPs present in wild-type tobacco plants. Immuno-dot blotting of the product, using anti-AGP antibodies, showed that the CsAGP1 protein had the AGP epitopes common to AGP families. The transcription level of CsAGP1 in cucumber hypocotyls increased in response not only to GA but also to indole-3-acetic acid. Although CsAGP1 is expressed in most vegetative tissues of cucumber, including the shoot apices and roots, the GA treatment resulted in an increase in the mRNA level of CsAGP1 only in the upper part of the hypocotyls. Y(betaGlc)(3), which selectively binds AGPs, inhibited the hormone-promoted elongation of cucumber seedling hypocotyls. Transgenic plants ectopically expressing CsAGP1 showed a taller stature and earlier flowering than the wild-type plants. These observations suggest that CsAGP1 is involved in stem elongation. (+info)
Nucleotide sequence and genome organization of Cucumber yellows virus, a member of the genus Crinivirus.
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The genome of Cucumber yellows virus (CuYV), isolated in Japan from cucumber (Cucumis sativus L.), was completely sequenced and shown to be bipartite. CuYV RNA1 consisted of 7889 nucleotides and encompassed seven open reading frames (ORFs), which is typical of the Closteroviridae, including a heat-shock protein 70 homologue, a coat protein and a diverged coat protein (CPd). CuYV RNA2 consisted of 7607 nucleotides and included two ORFs: ORF1a potentially encoded a polyprotein containing putative papain-like protease, methyltransferase and helicase domains, and ORF 1b potentially encoded an RNA-dependent RNA polymerase, which is probably expressed via a +1 ribosomal frameshift. The size and organization of the CuYV genome are similar to those of Lettuce infectious yellows virus (LIYV), the type member of the genus Crinivirus in the family Closteroviridae, indicating that CuYV is a member of that genus, although CuYV differed in several points from LIYV. (+info)