The influence of photoperiod on incorporation of precursors into tocopherols and plastoquinone in Xanthium strumarium L.

Radioactivity from tyrosine applied to leaves of Xanthium strumarium L. was incorporated into α- and γ-tocopherol and plastoquinone. Time-course studies on vegetative plants showed that γ-tocopherol was rapidly labelled and turned over, while α-tocopherol showed no sign of turnover. The same pattern was observed in the light and in darkness. Plastoquinone synthesis was rapid in the light but it was greatly reduced in the dark. Following floral induction the accumulation of radioactivity in γ-tocopherol was at first slower, but it later readied higher levels than in the vegetative plants. Total incorporation into α-tocopherol and plastoquinone was greatly reduced.

Metabolism of 4-chloro-2-methylphenoxyacetate by a soil pseudomonad. Preliminary evidence for the metabolic pathway.

1. A pseudomonad capable of utilizing the herbicide 4-chloro-2-methylphenoxyacetate as a sole carbon source was isolated from soil and cultured in liquid medium. 2. Analysis of induction patterns of 4-chloro-2-methylphenoxyacetate-grown cells suggests that 5-chloro-o-cresol and 5-chloro-3-methylcatechol are early intermediates in the oxidation of 4-chloro-2-methylphenoxyacetate. Cells were not adapted to oxidize 4-chloro-6-hydroxy-2-methylphenoxyacetate. 3. In culture, 4-chloro-2-methylphenoxyacetate rapidly disappeared and the chlorine in the molecule was quantitatively released as Cl(-) ion. 4. A lactone (gamma-carboxymethylene-alpha-methyl-Delta(alphabeta)-butenolide) was isolated from cultures and established as an intermediate. 5. The following metabolic pathway is suggested: 4-chloro-2-methylphenoxyacetate --> 5-chloro-o-cresol --> 5-chloro-3-methylcatechol --> cis-cis-gamma-chloro-alpha-methylmuconate --> gamma-carboxymethylene-alpha-methyl-Delta(alphabeta)-butenolide --> gamma-hydroxy-alpha-methylmuconate. 6. The tentative identification of 5-chloro-o-cresol, a gamma-chloro-alpha-methylmuconate and gamma-hydroxy-alpha-methylmuconate in culture extracts supports this scheme. However, the catechol was never observed to accumulate in cultures. 7. The detection of 4-chloro-6-hydroxy-2-methylphenoxyacetate, 2-methyl-phenoxyacetate, a dehalogenated cresol and oxalate in culture extracts is discussed in relation to the proposed metabolic pathway.

Bacterial metabolism of 4-chloro-2-methylphenoxyacetate. Formation of glyoxylate by side-chain cleavage.

Crude extracts of Pseudomonas sp. grown on 4-chloro-2-methylphenoxyacetate as sole source of carbon were shown to oxidize 4-chloro-2-methylphenoxyacetate to 5-chloro-o-cresol and glyoxylate. A labelled 2,4-dinitrophenylhydrazone was isolated from an incubation mixture in which 4-chloro-2-methylphenoxy[carboxy-(14)C]acetate was used. The hydrazone was shown to behave identically on thin-layer chromatograms with the authentic 2,4-dinitrophenylhydrazone of glyoxylate. Radioactivity assay showed that 82% of the side chain of 4-chloro-2-methylphenoxyacetate was recovered as glyoxylate.

Metabolism of 4-chloro-2-methylphenoxyacetate by a soil pseudomonad. Ring-fission, lactonizing and delactonizing enzymes.

1. A cell-free system, prepared from Pseudomonas N.C.I.B. 9340 grown on 4-chloro-2-methylphenoxyacetate (MCPA) was shown to catalyse the reaction sequence: 5-chloro-3-methylcatechol --> cis-cis-gamma-chloro-alpha-methylmuconate --> gamma-carboxymethylene-alpha-methyl-Delta(alphabeta)-butenolide --> gamma-hydroxy-alpha-methylmuconate. 2. The activity of the three enzymes involved in these reactions was completely resolved and the lactonizing and delactonizing enzymes were separated. 3. This part of the metabolic pathway of 4-chloro-2-methylphenoxyacetate is thus confirmed for this bacterium. 4. The ring-fission oxygenase required Fe(2+) or Fe(3+) and reduced glutathione for activity; the lactonizing enzyme is stimulated by Mn(2+), Mg(2+), Co(2+) and Fe(2+); no cofactor requirement could be demonstrated for the delactonizing enzyme. 5. cis-cis-gamma-Chloro-alpha-methylmuconic acid was isolated and found to be somewhat unstable, readily lactonizing to gamma-carboxymethylene-alpha-methyl-Delta(alphabeta)-butenolide. 6. Enzymically the lactonization appears to be a single-step dehydrochlorinase reaction.

Uptake and metabolism of vitamins e and k by pea stem sections.

The uptake of alpha-tocopherol and vitamin K(1) by pea stem sections is described. Vitamin K(1) appears to be stable within the plant tissue and is found distributed in all particulate cell fractions following uptake. Only a small proportion of the tocopherol taken up is recoverable and the majority of the compound appears to undergo catabolism.The oxidation of tocopherols by a cell-free system is described. This system requires oxygen and appears to involve enzyme activity but does not appear to be linked with the action of lipoxidase.

Analysis and distribution of tocopherols and quinones in the pea plant.

A procedure is described and evaluated for the analysis of ubiquinone, plastoquinone, tocopherols and vitamin K(1) in Pisum sativum L. Vitamin K(1) appears to be absent from the roots of this plant. While the pea seed contains only gamma-tocopherol, the root and shoot contain only alpha-tocopherol. During the greening of etiolated tissue, plastoquinone and vitamin K(1) levels increase markedly while ubiquinone and alpha-tocopherol levels are unaffected. On homogenization or damage to tissue, considerable losses of alpha-tocopherol occur in the pea plant.