Journal Article

Methylation reactions and the phytoalexin response in alfalfa suspension cultures

Gregory, A.C.E. (Durham Univ. (United Kingdom). Dept. of Biological Sciences), Daniell, T.J, Edwards, R

1997

Overview

In order to determine why the activated methyl cycle is up-regulated in plants undergoing defence responses to fungal pathogens we have monitored the utilisation of methyl groups derived from methionine in cell-suspension cultures of alfalfa (Medicago sativa L.) treated for various times with fungal elicitor, by carrying out a parallel labelling study with [35S]methionine and [methyl-3H]methionine. The distribution of the two radiolabels among the medium, soluble cellular components and cell wall was then determined. In the absence of elicitor the utilisation of the two radiolabels was similar. However, in the presence of the elicitor the total incorporation of radioactivity from [methyl-3H]methionine into metabolites was far greater than from [35S]methionine, indicating that the methyl label had been utilised in methylation reactions. Elicitor treatment resulted in up to a sixfold increase in the use of 3H-methyl groups in the methylation of hydrophobic metabolites. In the period 0—24 h after elicitor treatment, increased methylation was directed largely into the synthesis of the isoflavonoid phytoalexin medicarpin and related metabolites. Newly synthesized phytoalexins were exported into the medium, while a significant proportion of the medicarpin accumulating in the cell in the early stages of elicitation was derived from the hydrolysis of its respective conjugate. Elicitor treatment also modified the incorporation of 3H-methyl groups into the cell wall. Between 0 and 24 h after elicitor treatment the methylation of pectin in the cell wall declined. After 24 h, pectin methylation recovered and was associated with an increase in the methylation of other wall-bound polysaccharide components. Since no other major metabolic sink for the increased methylation was determined we conclude that the increased activity of the activated methyl cycle during defence interactions in alfalfa is required to support phytoalexin synthesis and cell wall modifications.

• Publisher: Springer-Verlag,Springer,Springer Nature B.V
• Subject: Acetates / ACTIVIDAD ENZIMATICA / ACTIVITE ENZYMATIQUE / AGENT PATHOGENE / Alfalfa / Bacteria / Biological and medical sciences / Cell culture techniques / cell suspension culture / Cell wall components / CELL WALLS / Cellular metabolism / Cultured cells / Elicitor / ENFERMEDADES FUNGOSAS / ENZYMIC ACTIVITY / FITOALEXINA / FLAVONOIDE / FLAVONOIDES / FLAVONOIDS / Fundamental and applied biological sciences. Psychology / FUNGAL DISEASES / Fungal plant pathogens / Fungi / Hydrophobicity / isotopes / Labeling / MALADIE FONGIQUE / MEDICAGO SATIVA / Medicarpin / METABOLISM / METABOLISME / METABOLISMO / Metabolites / METHIONINE / METHYLATION / METILACION / METIONINA / ORGANISMOS PATOGENOS / PARED CELULAR / PAROI CELLULAIRE / PATHOGENS / Pathology, epidemiology, host-fungus relationships. Damages, economic importance / Pectin / pectins / PHYTOALEXINE / PHYTOALEXINS / Phytopathology. Animal pests. Plant and forest protection / Plants / POLISACARIDOS / POLYHOLOSIDE / POLYSACCHARIDES / proteins / Radioactive decay / Radioactivity / radioaktive Markierung / Saccharomyces cerevisiae / solubility / Stoffwechsel / sulfur / Synthesis / TECHNIQUE DES TRACEURS / TECNICAS DE TRAZADORES / TRACER TECHNIQUES / tritium / Zellsuspension