Methyl-beta-D-glucopyranoside in higher plants: accumulation and intracellular localization in Geum montanum L. leaves and in model systems studied by C-13 nuclear magnetic resonance
Résumé
Using C-13-NMR, methyl-beta-D-glucopyranoside (MeG) was characterized as a major compound in the leaves of the alpine herb Geum montanum L. MeG continuously accumulated during the life span of G. montanum leaves, and accounted for up to 20% of the soluble carbohydrates in aged overwintering leaves, without being reallocated during senescence. Incubating intact plant tissues, culture cells, and purified organelles with C-13-labelled substrates showed that MeG was synthesized in the cytosol of cells, directly from glucose and methanol molecules. There was no contribution of the C-1 pathway. MeG was subsequently stored in the vacuole without being re-exported to the cytoplasm. All the dicots tested contained the enzymatic machinery permitting MeG synthesis from methanol and glucose, but the plants accumulating this compound at concentrations higher than 1 mumol g(-1) wet wt were mainly members of the Rosaceae family belonging to the Rosoideae subfamily. It is suggested that the synthesis of MeG may contribute to reduce the accumulation in the cytoplasm of methanol and its derived compounds.