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Analysis of bud exudates of Populus deltoides , P. fremontii , P. sargentii and P. wislizenii (Section Aigeiros ) by GC-MS identified a total of 78 components, of which 58 were phenolics. The composition of the bud exudate of all four species was highly similar, the most abundant components being pinocembrin and its chalcone, pinobanksin and its 3-methyl ether, pinobanksin-3-acetate and galangin.

The nove 3-methyl-3-butenyl, 2-methyl-2-butenyl, 3-methyl-2-butenyl and 2-phenylethyl esters of 3-acetyloxycaffeic acid and 4-acetyloxycaffeic acid were synthesised on a micro scale and characterised by gas chromatography—mass spectrometry. These compounds are identified for the first tiem in poplar bud exudates.

Analysis by GC-MS separated 50 components of bud exudate from P. sieboldii (Section Leuce ) of which 36 were phenolics. The bulk of the bud exudate (66.7%) was composed of the flavanone naringenin and its methyl ethers sakuranetin and isosakuranetin, together with their corresponding chalcones. These flavanones are minor components (

GC-MS analysis of bud exudate composition of a number of poplars of the section Leuce indicated that Populus alba, P. grandidentata and P. tomentosa were similar in secreting bud exudate containing only hydrocarbon material whereas P. sieboldii, P. tremula and P. tremuloides secreted bud exudate which also included phenolics. The latter three species were distinct from other poplars in secreting an exudate containing flavanones produced only by the first steps of flavonoid biosynthesis, such as naringenin and its methyl ethers, sakuranetin and isosakuranetin, together with their chalcones. Principal component analysis indicated that there are hybrids which are not clearly distinct morphologically from one of the parent species.

The complex mixture of phenolic compounds which is present in the bud exudate of many poplars may be resolved by single ion reconstructions of gas chromatography-mass spectrometry data. The prominent [M − 15]+ ions of the trimethylsilyl derivatives of chalcones, dihydrochalcones, flavones and flavanones render them particularly suitable for location by single ion reconstructions.

GC-MS analysis of bud exudate composition of Populus angustifolia indicated that it was not related chemotaxonomically to the sect. Tacamahaca poplars P. balsamifera and P. trichocarpa but was related to the sect. Aigeiros poplars P. deltoides and P. nigra .

Analysis by GC-MS separated 52 components from the bud exudate of P. ciliata of which 38 were phenolics. The exudate was unusual in completely lacking the flavonoids which occur in most poplar bud exudates. Over 70% of the exudate consisted of esters of caffeic acid or acetyloxycafreic acids.

Analysis by GC-MS identified 57 phenolic compounds in the bud exudate of Populus trichocarpa. Of these 11 have not been previously identified in poplar bud exudate. The bulk of the exudate was composed of acetophenones, substituted benzoic acids and their esters, cinnamic acid and its esters, dihydrochalcones, terpenoids and hydrocarbons.

Analysis by GC-MS separated 59 components of the bud exudate from Populus euphratica of which 37 were phenolics. The bulk of the exudate was composed of phenylpropenoic acids and their glyceryl-, monoacetyl glyceryl-and diacetyl glyceryl-esters. Flavonoids, common in many poplar exudates, were lacking.

Cysteinyl- and methionyl-tRNA synthetases (EC 6.1.1.-) were purified 1200and 1000-fold, respectively, from sonic extracts of Paracoccus denitrificans strain 8944, and kinetics, substrate specificity and regulatory properties were determined using the ATP-PP i exchange reaction. Both enzymes had pH optima of approx. 8 and were inhibited by sulphydryl-group reagents. Cysteinyl-tRNA synthetase catalysed l -selenocysteine- and α-aminobutyric acid-dependent ATP-PP i exchange and methionyl-tRNA synthetase catalysed l -homocysteine-, l -selenomethionine- and norleucine-dependent ATP-PPg exchange. Both enzymes were inhibited by O -acetylserine. Cysteinyl-tRNA synthetase activity was stimulated by methionine and methionyl-tRNA synthetase activity was stimulated by sulphide, cysteine, and cysteic acid.

We here identify five chalcones and six dihydrochalcones. Of these, three chalcones and five dihydrochalcones have not, we believe, been previously identified in Populus bud exudate. The technique of GC-MS has not been previously applied successfully to the resolution of such a complex mixture

1. 1.Serine transacetylase, O-acetylserine sulphydrylase and β-cystathionase were purified from Paracoccus denitrificans strain 8944. 2. 2.Serine transacetylase was purified 150-fold. The enzyme has a pH optimum between 7.5 and 8.0, is specific for l -serine and is inhibited by sulphydryl-group reagents. The apparent Km values for serine and acetyl-CoA are 4.0 · 10−4 and 1.0 · 10−4 M, respectively. Serine transacetylase is strongly inhibited by cysteine. 3. 3.O-Acetylserine sulphydrylase was purified 450-fold. The enzyme has a sharp pH optimum at pH 7.5. In addition to catalysing the synthesis of cysteine, O-acetylserine sulphydrylase catalyses the synthesis of selenocysteine from Oacetylserine and selenide. The Km values for sulphide and O-acetylserine are 2.7 · 10−3 and 1.25 · 10−3 M, respectively. The enzyme was stimulated by pyridoxal phosphate and was inhibited by cystathionine, homocysteine and methionine. 4. 4.β-Cystathionase was purified approx. 50-fold. β-Cystathionase has a pH optimum between pH 9.0 and 9.5, is sensitive to sulphydryl-group reagents, required pyridoxal phosphate for maximum activity and has an apparent Km for cystathionine of 4.2 · 10−3 M. β-Cystathionase also catalyses the release of keto acid from lanthionine, djenkolic acid and cystine. Cysteine, O-acetylserine, homocysteine and glutathione strongly inhibit β-cystathionase activity and homocysteine and methionine represses enzyme activity. 5. 5.O-Acetylserine lyase was identified in crude extracts of Paracoccus denitrificans. The enzyme is specific for O- acetyl- l -serine , requires pyridoxal phosphate and is inhibited by KCN and hydroxylamine. The enzyme has a high Km value for O-acetylserine (50–100 mM).

The summer bud exudate of two plants of P. lasiocarpa analysed by GC/MS lacked the flavonoid aglycones and substituted benzoic and phenolic acid esters characteristic of other poplar species. Other compounds, such as syringaldehyde, syringic acid and shikimic acid, not previously identified in bud exudate of other poplar species were found, as were catechin, catechol, quinic acid and salicin, compounds not normally present in poplar bud exudate. The exudates from the two sources differed considerably in detailed composition.

4,4′-Dihydroxytruxillic acid was released from the cell walls of Lolium multiflorum by treatment with sodium hydroxide. Combined gas chromatography-mass spectrometry indicated that other similar dimers, probably resulting from the photodimerization of p-coumaric acid or ferulic acid, were also released from the cell walls. The possible role of the dimers in cross-linking cell wall heteroxylans is discussed.