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Results for “Phenols/metabolism”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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3 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

The western red cedar (Thuja plicata) 8-8' DIRIGENT family displays diverse expression patterns and conserved monolignol coupling specificity

The isolation and characterization of a multigene family of the first class of dirigent proteins (namely that mainly involved in 8-8' coupling leading to (+)-pinoresinol in this case) is reported, this comprising of nine western red cedar (Thuja plicata) DIRIGENT genes (DIR1-9) of 72-99.5% identity to each other. Their corresponding cDNA clones had coding regions for 180-183 amino acids with each having a predicted molecular mass of ca. 20 kDa including the signal peptide. Real time-PCR established that the DIRIGENT isovariants were differentially expressed during growth and development of T. plicata (P < 0.05). The phylogenetic relationships and the rates and patterns of nucleotide substitution suggest that the DIRIGENT gene may have evolved via paralogous expansion at an early stage of vascular plant diversification. Thereafter, western red cedar paralogues have maintained an high homogeneity presumably via a concerted evolutionary mode. This, in turn, is assumed to be the driving force for the differential formation of 8-8'-linked pinoresinol derived (poly)lignans in the needles, stems, bark and branches, as well as for massive accumulation of 8-8'-linked plicatic acid-derived (poly)lignans in heartwood.

Non-NASA Center↗
NASA NTRS1995

Towards the specification of consecutive steps in macromolecular lignin assembly

When Pinus taeda cell suspension cultures are exposed to 8% sucrose solution, the cells undergo significant intracellular disruption, irregular wall thickening/lignification with concomitant formation of an 'extracellular lignin precipitate. However, addition of potassium iodide (KI), an H202 scavenger, inhibits this lignification response, while the ability to synthesize the monolignols, p-coumaryl and coniferyl alcohols, is retained. Lignin synthesis (i.e. polymerization) is thus temporarily correlated with H202 generation, strongly implying a regulatory role for the latter. Time course analyses of extracellular metabolites leading up to polymer formation reveal that coniferyl alcohol, but not p-coumaryl alcohol, undergoes substantial coupling reactions to give various lignans. Of these, the metabolites, dihydrodehydrodiconiferyl alcohol, shonanin (divanillyl tetrahydrofuran) and its apparent aryl tetralin derivative, cannot be explained simply on the basis of phenolic coupling. It is proposed that these moieties are the precursors of so-called reduced substructures in the lignin macromolecule. This adds a new perspective to the lignin assembly mechanism.

Non-NASA Center↗
NASA NTRS2001

Dirigent proteins and dirigent sites in lignifying tissues

Tissue-specific dirigent protein gene expression and associated dirigent (site) localization were examined in various organs of Forsythia intermedia using tissue printing, in situ mRNA hybridization and immunolabeling techniques, respectively. Dirigent protein gene expression was primarily noted in the undifferentiated cambial regions of stem sections, whereas dirigent protein sites were detected mainly in the vascular cambium and ray parenchyma cell initials. Immunolocalization also revealed cross-reactivity with particular regions of the lignified cell walls, these being coincident with the known sites of initiation of lignin deposition. These latter regions are considered to harbor contiguous arrays of dirigent (monomer binding) sites for initiation of lignin biopolymer assembly. Dirigent protein mRNA expression was also localized in the vascular regions of roots and petioles, whereas in leaves the dirigent sites were primarily associated with the palisade layers and the vascular bundle. That is, dirigent protein mediated lignan biosynthesis was initiated primarily in the cambium and ray cell initial regions of stems as well as in the leaf palisade layers, this being in accordance with the occurrence of the lignans for defense purposes. Within lignified secondary xylem cell walls, however, dirigent sites were primarily localized in the S(1) sublayer and compound middle lamella, these being coincident with previously established sites for initiation of macromolecular lignin biosynthesis. Once initiation occurs, lignification is proposed to continue through template polymerization.

NASA Discipline Plant Biology↗