Etsuo Yamamoto

Monitoring biosynthesis of wheat cell-wall phenylpropanoids in situ.

Lignins and suberins are complex plant cell-wall macromolecules that are composed mainly of phenylpropanoid residues derived from L-phenylalanine. Lignins and suberins are considered to be covalently linked to carbohydrates and to lipids, respectively. The bonding of these important structural materials within cell walls has never been established. By feeding specifically labeled [13C] ferulic acid over extended durations to seedlings of Triticum aestivum L. and by using solid-state carbon-13 nuclear magnetic resonance techniques, the major resonances due to specific carbons in the propanoid side chains of these cell-wall polymers have been identified in situ. The signals were found to differ significantly from those of synthetic lignins, which have usually been considered to be good approximations of natural lignin structure.

Tannins — Their Place in Plant Metabolism

Terrestrial vascular plants synthesize, in addition to structural polymers like cellulose and lignin, a rather bewildering array of metabolic products, such as lignans, phenolic acids, tannins, alkaloids, terpenoids etc. Excluding the structural polymers, the functions of many of these compounds (i.e., so-called secondary metabolites) are not well understood. This chapter presents an overview of the metabolism of phenylpropanoids, particularly hydrolyzable and condensed tannins, and then reexamines these pathways in the context of their relationships to general plant metabolism. Calculations show that the cost of diversion of biochemical energy of living plants into tannins is high compared to energy requirements for the structural cell wall polysaccharides. Hence, in many high-tannin-content plants, tannin synthesis contributes significantly to captured photosynthetic energy usage. Phenylpropanoid (hence, tannin) synthesis is also particularly important to nitrogen recycling.

5-hydroxyferulic acid in Zea mays and Hordeum vulgare cell walls

Abstract Considerable amounts of esterified E -5-hydroxyferulic acid and very small amounts of esterified E -sinapic acid were detected and identified in cell walls of young Zea mays and Hordeum vulgare , in addition to known E - p -coumaric and ferulic acids. Their relative amounts were determined by peak areas using GC. The ratios of E - p -coumaric-5-hydroxyferulic-sinapic-ferulic acid were 440:46:2:100 in corn, and 37:26:3:100 in barley, respectively.

Lignan biosynthesis in forsythia species

Both (+)-pinoresinol 6a in Forsythia suspensa and (–)-secoisolariciresinol 14a in F. intermedia are formed via a direct stereochemically-controlled coupling of coniferyl alcohol 2 derived moieties (cf. the typical peroxidase-catalysed reaction in the presence of H2O2), and the dibenzylbutyrolactone lignan, (–)-matairesinol 10a, in F. intermedia is formed from a post-coupling modification of (–)-secoisolariciresinol 14a; this transformation has been demonstrated in vivo, and in vitro with a crude enzyme preparation, and represents the first report of an enzyme specifically involved in lignan biosynthesis.

High-performance liquid chromatographic separation of E- and Z-monolignols and their glucosides

Abstract Photoirradiation of the E -monolignols, E-p -coumaryl, coniferyl and sinapyl alcohols gave mixtures of the corresponding E/Z monolignols. Similar treatments of the glucosides, E - and Z -coniferin, Z -isoconiferin and Z -isoconiferin and Z -syringin afforded comparable E/Z mixtures. Without derivatization, separation of the individual E - and Z -monolignols, and the E - and Z -monolignol glucosides could only be obtained by high-performance liquid chromatography. This development now permits the long-awaited facile analysis of plant extracts for E/Z monolignol and corresponding glucoside composition.

Exclusive accumulation of Z-isomers of monolignols and their glucosides in bark of Fagus grandifolia

In addition to Z-coniferyl and Z-sinapyl alcohols, bark extracts of Fagus grandifolia also contain significant amounts of the glucosides, Z-coniferin, Z-isoconiferin (previously called faguside) and Z-syringin. The corresponding E-isomers of these glucosides do not accumulate to a detectable level. The accumulation of the Z-isomers suggests that either they are not lignin precursors or that they are reservoirs of monolignols for subsequent lignin biosynthesis; it is not possible to distinguish between these alternatives. The co-occurrence of Z-coniferin and Z-isoconiferin demonstrate that glucosylation of monolignols can occur at either the phenolic or the allylic hydroxyl groups.

The E/Z isomerization step in the biosynthesis of Z-coniferyl alcohol in Fagus grandifolia

Abstract Beech bark contains significant amounts of Z-coniferyl and Z-sinapyl alcohols but not the corresponding E-isomers. There are a number of steps along the cinnamate pathway where E/Z isomerism of the cinnamyl double bond could occur. Studies of the conversion, in beech bark, of 14C-labelled E- and Z-ferulic acids, E-coniferylaldehyde and E- and Z-coniferyl alcohols indicate that this isomerism occurs at the level of the hydroxycinnamyl alcohols. This system differs, therefore, from that described for the isomerism of geraniol to nerol which proceeds via the corresponding aldehyde.

Incorporation of [2-13C]ferulic acid, a lignin precursor, into Leucaena leucocephala and its analysis by solid state 13C n.m.r. spectroscopy

Solid state 13C n.m.r. analysis of lignin in situ, in the root tissue of the woody angiosperm, Leucaena leucocephala, and specifically labelled at a carbon site thought to be involved in the majority of inter-unit linkages, revealed significant bonding differences when compared to an artificial lignin preparation generally viewed more or less to represent native lignin structure.