The mathematical treatment of leaf venation: the variation in secondary vein length along the midrib.
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BACKGROUND AND AIMS: In some dicotyledonous leaves and leaflets, the secondary veins run more-or-less straight to the margins and have well-defined lengths. For a given half-lamina of length L, an equation, previously proposed, relates the lengths of these veins, p, to the distances, l, between the leaf tip and their insertions on the midrib: p = B2(x+y)l(x)(L - l)(y)/L(x+y-1), where B, x and y are fitted parameters. Aspects of the formula are re-examined, including its general applicability, significance and usefulness. METHODS: Length measurements were made on leaves of various dicotyledons, notably Ulmus glabra, U. procera, Alnus viridis, A. glutinosa, Corylus avellana and Crataegus monogyna. Equations were fitted by non-linear regression. KEY RESULTS: The equation has now been applied descriptively to 23 species of eight families, but it is sometimes preferable or necessary to replace the measured length, L, with a fourth parameter that may differ significantly from it. Within a given species, values of the indices x and y are positively correlated. Leaves of some U. glabra depart qualitatively from the general pattern. As an example of hypothesis testing, the equation was used to show that the retuse or emarginate leaf tips of A. glutinosa are not due to stunting. CONCLUSIONS; That the equation applies to many species suggests that the underlying processes of leaf growth are quantitatively similar. Although relevant knowledge of these is scant, consideration of mathematical relationships may help their elucidation. (+info)
Fluctuation of endophytic bacteria and phytoplasmosis in elm trees.
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A total of 658 heterotrophic bacterial colonies isolated from phloem tissues of roots and branches in four months (April, June, September and December) from two elm plants, one of which affected by phytoplasmosis, were typed by means of ARDRA. This analysis revealed the existence of a high degree of variability within the community and was able to detect 84 different ARDRA groups. The Analysis of Molecular Variance was applied to ARDRA patterns to analyze the differentiation between communities isolated from the various samplings. Data obtained were compared with those from a previous work (Mocali et al. 2003). Results indicated that plants with symptoms of phytoplasmosis showed marked alterations in the extent of the fluctuations of the community along the seasons in the different plant organs. (+info)
Inoculum size effect in dimorphic fungi: extracellular control of yeast-mycelium dimorphism in Ceratocystis ulmi.
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We studied the inoculum size effect in Ceratocystis ulmi, the dimorphic fungus that causes Dutch elm disease. In a defined glucose-proline-salts medium, cells develop as budding yeasts when inoculated at > or = 10(6) spores per ml and as mycelia when inoculated at <10(6) spores per ml. The inoculum size effect was not influenced by inoculum spore type, age of the spores, temperature, pH, oxygen availability, trace metals, sulfur source, phosphorous source, or the concentration of glucose or proline. Similarly, it was not influenced by added adenosine, reducing agents, methyl donors, amino sugars, fatty acids, or carbon dioxide. Instead, growing cells excreted an unknown quorum-sensing factor that caused a morphological shift from mycelia to budding yeasts. This yeast-promoting effect is abolished if it is extracted with an organic solvent such as ethyl acetate. The quorum-sensing activity acquired by the organic solvent could be added back to fresh medium in a dose-dependent fashion. The quorum-sensing activity in C. ulmi spent medium was specific for C. ulmi and had no effect on the dimorphic fungus Candida albicans or the photomorphogenic fungus Penicillium isariaeforme. In addition, farnesol, the quorum-sensing molecule produced by C. albicans, did not inhibit mycelial development of C. ulmi when present at concentrations of up to 100 microM. We conclude that the inoculum size effect is a manifestation of a quorum-sensing system that is mediated by an excreted extracellular molecule, and we suggest that quorum sensing is a general phenomenon in dimorphic fungi. (+info)
Classification of phytoplasma strains in the elm yellows group (16SrV) and proposal of 'Candidatus Phytoplasma ulmi' for the phytoplasma associated with elm yellows.
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Elm yellows group (16SrV) phytoplasmas, which are associated with devastating diseases in elm, grapevine, blackberry, cherry, peach and several other plant species in America, Europe and Asia, represent one of the most diverse phytoplasma clusters. On the basis of phylogenetic analysis of 16S rDNA sequences, elm yellows group phytoplasmas form a discrete subclade within the phytoplasma clade. Three phylogenetic parameters, namely 16S rRNA, ribosomal protein and secY genes, have been evaluated for their usefulness in differentiating elm yellows group phytoplasmas. RFLP analysis of 16S rRNA sequences differentiated the elm yellows group phytoplasmas into five subgroups. Twelve RFLP subgroups were differentiated on the basis of ribosomal protein and 13 were differentiated using secY gene sequences. Phylogenetic analysis of the ribosomal protein genes and secY gene alone or in combination indicated that the subgroups constitute 12 genetically distinct lineages, each of which appears to have evolved under different ecological constraints such as specific vector or plant hosts. On the basis of unique DNA and biological properties, it is proposed that the elm yellows phytoplasma EY1(T) represents a novel taxon, 'Candidatus Phytoplasma ulmi'. (+info)
Microbacterium ulmi sp. nov., a xylanolytic, phosphate-solubilizing bacterium isolated from sawdust of Ulmus nigra.
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A xylanolytic and phosphate-solubilizing bacterium isolated from sawdust of Ulmus nigra in Salamanca was characterized by a polyphasic approach. The novel strain, designated XIL02(T), was Gram-positive, aerobic, catalase- and oxidase-negative, rod-shaped and non-motile. Phylogenetically and chemotaxonomically, it was related to members of the genus Microbacterium. According to 16S rRNA gene sequence analysis, it is closely related to Microbacterium arborescens and Microbacterium imperiale; however, DNA-DNA hybridization showed reassociation values less than 70 % with the type strains of these species. In chemotaxonomic analyses, the major menaquinones detected were MK-12, MK-13 and MK-11 and the major fatty acids were anteiso-C(15 : 0), anteiso-C(17 : 0) and iso-C(16 : 0); the peptidoglycan was of the type B2beta. The G+C content determined was 69 mol%. Based on the present data, it is proposed that strain XIL02(T) (=LMG 20991(T)=CECT 5976(T)) be classified as the type strain of a novel Microbacterium species, for which the name Microbacterium ulmi sp. nov. is proposed. (+info)
Cellulomonas xylanilytica sp. nov., a cellulolytic and xylanolytic bacterium isolated from a decayed elm tree.
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A Gram-positive, aerobic, non-motile bacterium was isolated from a decayed elm tree. Phylogenetic analysis based on 16S rDNA sequences revealed 99.0 % similarity to Cellulomonas humilata. Chemotaxonomic data that were determined for this isolate included cell-wall composition, fatty acid profiles and polar lipids; the results supported the placement of strain XIL11(T) in the genus Cellulomonas. The DNA G+C content was 73 mol%. The results of DNA-DNA hybridization with C. humilata ATCC 25174(T), in combination with chemotaxonomic and physiological data, demonstrated that isolate XIL11(T) should be classified as a novel Cellulomonas species. The name Cellulomonas xylanilytica sp. nov. is proposed, with strain XIL11(T) (=LMG 21723(T)=CECT 5729(T)) as the type strain. (+info)
Cytotoxic effects of mansonone E and F isolated from Ulmus pumila.
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Two sesquiterpenoids, mansonone E (ME) and mansonone F (MF) were first isolated from the dried root bark of Ulmus pumila (shironire in Japanese), and their antiproliferative activities on human tumor cells were evaluated in vitro. ME had more potent cytotoxic effects on four tumor cell lines, human cervical cancer HeLa, human malignant melanoma A375-S2, human breast cancer MCF-7, and human histiocytic lymphoma U937, than those of MF. The results showed that ME induced oligonucleosomal fragmentation of DNA in HeLa cells and activated caspase-3, followed by the degradation of the inhibitor of caspase-activated DNase, decreased the expression of anti-apoptotic mitochondrial proteins Bcl-2 and Bcl-(XL), and increased that of proapoptotic Bax. (+info)
Effects of sand burial on survival, growth, gas exchange and biomass allocation of Ulmus pumila seedlings in the Hunshandak Sandland, China.
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BACKGROUND AND AIMS: In the last decade, the number of young plants of Ulmus pumila in the Hunshandak Sandland has decreased sharply because of severe sand burial, and their ecological protective function has been weakened. In order to develop an understanding of the tolerance of U. pumila to sand burial and to suggest reasonable measures to protect the sparse-elm-grassland ecosystem, the effects of burial on the survival, growth, photosynthesis and biomass allocation in U. pumila were studied. METHODS: Seedlings were buried at five different depths in pot experiments: no burial (control), partial burial (33 % and 67 % stem height), and complete burial (100 % and 133 % stem height). Growth analyses and measurements of photosynthesis were carried after the plants had been uncovered. KEY RESULTS: All the plants survived partial burial, but about 30 % and 80 % of the seedlings died as a result of the 100 % and 133 % sand burial treatments, respectively. The numbers of newly produced leaves and branches, and the height of the stems of the seedlings in the 33 % and 67 % burial treatments during the period of the experiment were significantly greater than those in the control. Furthermore, net photosynthetic rate, transpiration rate and water use efficiency were also elevated by the partial burial, but not affected by burial time. This might be attributed to the increased root length, which improved water acquisition. The biomass and biomass allocation of the seedlings were significantly changed by the burial treatments and burial times. The biomass was enhanced by partial burial but was reduced by complete burial at each burial time. However, the biomass allocation was not significantly changed by the 33 % and 67 % sand burial treatments 2 or 4 weeks following the burial. CONCLUSIONS: Ulmus pumila was shown to be tolerant to partial sand burial, but must be protected from complete burial. (+info)