Intracellular localization of sucrose‐phosphate phosphatase in storage cells

The intracellular location of sucrose‐phosphate phosphatase (SPP; EC 3.1, 3.24) was investigated by comparing the ratios of SPP to vacuolar and cytosolic markers in protoplasts and vacuoles from storage tissues of red beet ( Beta vulgaris ) and turnip ( Brassica rapa L. var. rapa ) hypocotyl, and carrot ( Daucus carota ) root. In all three instances, SPP activity was found not to be associated with vacuolar markers ß‐acetyl‐glucosaminidase and α‐mannosidase, but proportionally associated with the cytosolic marker alcohol dehydrogenase. It was determined that in storage cells of red beet and turnip hypocotyl, as well as in carrot root, SPP is located in the cytoplasm. Discrepancies with earlier reports indicating SPP of vacuolar origin are discussed.