EFFECTS OF VALIDAMYCIN-A, A POTENT TREHALASE INHIBITOR, AND PHYTOHORMONES ON TREHALOSE METABOLISM IN ROOTS AND ROOT-NODULES OF SOYBEAN AND COWPEA

Trehalose, a common microbial disaccharide, has been reported to be to xic to plants, and plant trehalase has therefore been hypothesized to function as a detoxifying enzyme. To test this, aseptically grown soyb ean (Glycine max L. Merr.) plantlets were supplied with trehalose. The plants accumulated trehalose only when validamycin A, a potent trehal ase inhibitor, was added as well. Under these conditions, they accumul ated trehalose to up to 8% of the dry weight in their primary leaves w ithout any detectable impairment of growth or health. We have previous ly shown that in soybean nodules, trehalose is generated by the symbio tic bacteria, and trehalase is strongly induced. However, direct expos ure of plants to trehalose did not affect their trehalase activity, wh ereas a treatment with auxin strongly increased it, indicating that th e enzyme level is regulated by hormones rather than by its substrate. Addition of validamycin A to nodules caused an increase in the amount of trehalose and a decrease in the sucrose and starch pools, but nitro gen fixation was not affected. Similar results were obtained with cowp ea (Vigna unguiculata L.) plantlets and nodules. These results indicat e that plant trehalase is functional in metabolizing trehalose from ex ogenous and endogenous sources, even though the disaccharide has no ob vious toxic effects.