IV. - CARACTÉRISTIQUES DE LA FRACTION GLUCIDIQUE DES ÉCHANTILLONS DE MAÏS GRAIN

International audienc

The Role of Auxin and Gibberellin in Controlling Lignin Formation in Primary Phloem Fibers and in Xylem of Coleus blumei Stems

The hypothesis that auxin (IAA) and gibberellic acid (GA(3)) control the formation of lignin is confirmed for the primary phloem fibers and for the secondary xylem in the stem of Coleus blumel Benth. Indoleacetic acid alone, or a combination of high IAA/low GA(3) (w/w), induced short phloem fibers with thick secondary walls, that contained lignin rich in syringyl units (high ratio of syringyl/guaiacyl). On the other hand, a combination of high GA(3)/low IAA (w/w), which promoted the differentiation of long phloem fibers with thin walls, decreased the relative content of the syringyl units (low syringyl/guaiacyl ratio). In the secondary xylem, these hormonal treatments yielded only slight changes in the noncondensed monomeric guaiacyl units, confirming the relative stability of the guaiacyl lignification pattern in this tissue. In the xylem, indoleacetic acid alone, or a combination of high IAA/low GA(3) induced lignin poor in syringyl units (low syringyl/guaiacyl ratio). A combination of high GA(3)/low IAA promoted a relatively slight increase in syringyl yield, indicating greater responsiveness of the syringyl lignification pattern to growth regulators. The possible functional and technological significance of our results is discussed

LE TOURTEAU DE COLZA EXEMPT DE THIOGLUCOSIDES OU DÉTOXIQUÉ PAR FERMENTATION. I. — UTILISATION DIGESTIVE DES GLUCIDES ET DE L'ÉNERGIE PAR LE PORC EN CROISSANCE

International audienc

Lignins with altered composition in the cell of transgenic plants

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Altered lignin composition in transgenic tobacco expressing O-methyltransferase sequences in sense and antisense orientation

International audienceThe monomeric composition of tobacco lignin has been modified by genetic engineering. Sense or antisense expression of sequences encoding O-methyltransferase (OMT), a lignin biosynthetic enzyme, was shown to modulate enzyme activity. Ten constructs harboring the entire or a partial OMT cDNA were used. Populations of 20 trensgenic plants per construct were analyzed for OMT activity and compared with untransformed controls. As expected, expression of only the full-length sense construct led to an increase in OMT activity. An important reduction of activity was found in a variable number of plantlets from all other transgenic populations but the inhibition was sustained through the adult stage only in plants transformed with the complete cDNA. T-DNA genes were shown to be stably integrated into the tobacco genome and to be transmitted to the progeny. By using gene-specific probes, OMT inhibition in stems was correlated to a parallel disappearance of OMT transcripts originating from both the resident gene and the transgene. In contrast, transgene transcripts were detected in leaf tissues where the resident gene is poorly expressed, thus indicating that relative expression of the two OMT genes controls transcript turnover. In stems of inhibited plants, a marked decrease of syringyl units and the appearance of 5-hydroxy guaiacyl units were demonstrated. These two structural features are also characteristic of natural mutants of maize with an improved digestibility compared with wild lines. These data demonstrate the feasibility and the potential benefits of lignin manipulation

Lignin composition in transgenic poplar plants with modified cinnamyl alcohol dehydrogenase activity with reference to dehydropolymer models of lignin

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Lignin composition in transgenic poplar plants with modified cinnamyl alcohol deshydrogenase activity with reference to dehydropolymer models of lignin

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