Subcellular Localization of a UDP-Glucose:Aldehyde Cyanohydrin β-Glucosyl Transferase in Epidermal Plastids of Sorghum Leaf Blades

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Abstract
Epidermal and mesophyll protoplasts, prepared from leaf blades of 6-day-old light-grown S. bicolor seedlings were separated by differential sedimentation and assayed for a number of enzymes. The epidermal protoplasts contained higher levels of NADPH-cytochrome c reductase (EC 1.6.2.4), triose phosphate isomerase (EC 5.3.1.1), phosphoenolpyruvate carboxylase (EC 4.1.1.31) and a UDP-glucose:cyanohydrin .beta.-glucosyl transferase (EC 2.4.1.85), but lower levels of NADP+ triosephosphate dehydrogenase (EC 1.2.1.13) than did mesophyll protoplasts. When protoplast preparations were lyzed and applied to linear sucrose density gradients, triosephosphate isomerase was present in epidermal plastids. A significant fraction (41%) of the glucosyl transferase activity was also associated with the epidermal plastids.