BETA-GLUCOSIDASE IN THE INDIGO PLANT - INTRACELLULAR-LOCALIZATION ANDTISSUE-SPECIFIC EXPRESSION IN LEAVES

beta-Glucosidase of indigo plant (Polygonum tinctorium) has a high sub strate specificity for indican (indoxyl beta-D-glucoside). To examine the localization of this beta-glucosidase, we fractionated the cells o f the leaves and analysed them immunocytochemically. Immunoelectron mi crographs with specific antibodies against the beta-glucosidase clearl y showed that the beta-glucosidase was localized in the stroma of the chloroplasts in mesophyll cells, but not in the thylakoid membrane. Ch loroplasts were isolated from the crude homogenate of the fresh leaves by Percoll density gradient centrifugation and then subjected to subo rganellar fractionation. beta-Glucosidase activity was specifically de tected in the stromal fraction, but not in the thylakoid membrane. Thi s was also supported by the result of an immunoblot of the fractions w ith anti-beta-glucosidase antibodies. The beta-glucosidase was immunoc ytochemically localized in the chloroplasts of mesophyll cells, but no t in any chloroplasts in marginal cells of the vascular bundle or epid ermal cells; ribulose 1,5-bisphosphate carboxylase (Rubisco), a typica l stromal protein, was observed in all chloroplasts in these cells. Th ese results suggest that beta-glucosidase is tissue specific in its ex pression in the leaves of the indigo plant.