The Metabolic Fate of (4-Chloro-2-Methylphenoxy)Acetic Acid in Higher Plants: II. METABOLISM IN LIQUID CULTURED CALLUS CELLS OF WHEAT (Triticum aestivum L. )

Callus cells of two wheat cultivars in liquid medium rapidlyabsorbed (4-chloro-2-methylphenoxy)acetic acid (MCPA) and convertedit to ethanol-soluble products. The herbicide was transformedby methyl-hydroxylation, the major terminal residue being analcoholic glycoside of (4-chloro-2-hydroxymethylphenoxy)aceticacid. Minor metabolites were an ether-soluble conjugate of MCPA,an MCPA-glycoside and five additional aglycones. No metaboliteswere released into the medium. The rate of metabolism was lowerthan that of uptake such that a substantial amount of the radioactivityinitially accumulating in the cells was unmodified MCPA. Metabolismwas qualitatively and quantitatively similar to that in shootsexcised from seedlings. Cells also absorbed an ether-solubleconjugate of MCPA which had been isolated from carrot (Daucuscarota L. ), though less readily than MCPA itself. MCPA andthe above metabolites were produced, with the alcoholic glycosideagain as the major residue. Some MCPA was present in the medium,due probably to the action of extracellular hydrolases. Key words: MCPA, Triticum aestivum, Cell culture, Hydroxylation