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Resultados filtrados por Publicador: American Society of Plant Biologists

‣ Separation of Arabidopsis Pollen Tetrads Is Regulated by QUARTET1, a Pectin Methylesterase Gene1[W]

Francis, Kirk E.; Lam, Sandy Y.; Copenhaver, Gregory P.
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /11/2006 Português
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163.1485%
Arabidopsis (Arabidopsis thaliana) QUARTET (QRT) genes are required for pollen separation during normal floral development. In qrt mutants, the four products of microsporogenesis remain fused and pollen grains are released as tetrads. In Arabidopsis, tetrad analysis in qrt mutants has been used to map all five centromeres, easily distinguish sporophytic from gametophytic mutations, and accurately assess crossover interference. Using a combination of forward and reverse genetics, we have identified the gene responsible for the qrt1 phenotype. Annotation predicts that QRT1 encodes a pectin methylesterase (PME), and enzymatic assays of QRT1 expressed in Escherichia coli indicate that QRT1 has PME activity. Promoter and transcription analysis demonstrate QRT1 is expressed in anther tissues shortly after meiosis is complete. Unexpectedly, the QRT1 promoter is also active in a variety of developmentally unrelated tissues, including developing guard cells, the hypocotyl-root transition zone, areas of lateral root emergence, and floral nectaries. PMEs constitute a large gene family in Arabidopsis, are involved in cell wall loosening, and have been implicated in various aspects of floral development and pollen tube elongation. The identification of QRT1 as a PME contributes to our understanding of pollen development and may help to provide valuable genetic tools in other plant species.

‣ Pectin Methyl Esterase Inhibits Intrusive and Symplastic Cell Growth in Developing Wood Cells of Populus12[W][OA]

Siedlecka, Anna; Wiklund, Susanne; Péronne, Marie-Amélie; Micheli, Fabienne; Leśniewska, Joanna; Sethson, Ingmar; Edlund, Ulf; Richard, Luc; Sundberg, Björn; Mellerowicz, Ewa J.
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /02/2008 Português
Relevância na Pesquisa
163.1485%
Wood cells, unlike most other cells in plants, grow by a unique combination of intrusive and symplastic growth. Fibers grow in diameter by diffuse symplastic growth, but they elongate solely by intrusive apical growth penetrating the pectin-rich middle lamella that cements neighboring cells together. In contrast, vessel elements grow in diameter by a combination of intrusive and symplastic growth. We demonstrate that an abundant pectin methyl esterase (PME; EC 3.1.1.11) from wood-forming tissues of hybrid aspen (Populus tremula × tremuloides) acts as a negative regulator of both symplastic and intrusive growth of developing wood cells. When PttPME1 expression was up- and down-regulated in transgenic aspen trees, the PME activity in wood-forming tissues was correspondingly altered. PME removes methyl ester groups from homogalacturonan (HG) and transgenic trees had modified HG methylesterification patterns, as demonstrated by two-dimensional nuclear magnetic resonance and immunostaining using PAM1 and LM7 antibodies. In situ distributions of PAM1 and LM7 epitopes revealed changes in pectin methylesterification in transgenic trees that were specifically localized in expanding wood cells. The results show that en block deesterification of HG by PttPME1 inhibits both symplastic growth and intrusive growth. PttPME1 is therefore involved in mechanisms determining fiber width and length in the wood of aspen trees.

‣ Cell Wall Polysaccharides Are Specifically Involved in the Exclusion of Aluminum from the Rice Root Apex1

Yang, Jian Li; Li, Ya Ying; Zhang, Yue Jiao; Zhang, Shan Shan; Wu, Yun Rong; Wu, Ping; Zheng, Shao Jian
Fonte: American Society of Plant Biologists Publicador: American Society of Plant Biologists
Tipo: Artigo de Revista Científica
Publicado em /02/2008 Português
Relevância na Pesquisa
163.1485%
Rice (Oryza sativa) is the most aluminum (Al)-resistant crop species among the small-grain cereals, but the mechanisms responsible for this trait are still unclear. Using two rice cultivars differing in Al resistance, rice sp. japonica ‘Nipponbare’ (an Al-resistant cultivar) and rice sp. indica ‘Zhefu802’ (an Al-sensitive cultivar), it was found that Al content in the root apex (0–10 mm) was significantly lower in Al-resistant ‘Nipponbare’ than in sensitive ‘Zhefu802’, with more of the Al localized to cell walls in ‘Zhefu802’, indicating that an Al exclusion mechanism is operating in ‘Nipponbare’. However, neither organic acid efflux nor changes in rhizosphere pH appear to be responsible for the Al exclusion. Interestingly, cell wall polysaccharides (pectin, hemicellulose 1, and hemicellulose 2) in the root apex were found to be significantly higher in ‘Zhefu802’ than in ‘Nipponbare’ in the absence of Al, and Al exposure increased root apex hemicellulose content more significantly in ‘Zhefu802’. Root tip cell wall pectin methylesterase (PME) activity was constitutively higher in ‘Zhefu802’ than in ‘Nipponbare’, although Al treatment resulted in increased PME activity in both cultivars. Immunolocalization of pectins showed a higher proportion of demethylated pectins in ‘Zhefu802’...