The Glucan Synthases from Suspension-Cultured Sugar Cane Cells

Organelles from 10 g phase suspension-cultured sugar cane cellshave been analysed by isopyenic sucrose density gradient centrifugation.The distribution profiles for marker enzymes have allowed therecognition of tonoplast, endoplasmic reticulum, Golgi apparatus,plasma membrane, mitochondrial and microbody fractions. In thissystem the glucan synthases I and II, which have previouslybeen regarded as specific marker enzymes for the Golgi apparatusand plasma membrane respectively, show a two-peak profile inthe gradient. For each glucan synthase the peaks correspondroughly with the positions of the Golgi apparatus and plasmamembrane. Analysis of the in vitro synthesized polymers fromthe glucan synthase assay indicates that a mixed-linked (ß,l 3; ß l 4) glucan is produced by both organelle fractions.Supported by individual observations from other authors we suggestthat, in the case of members of the Gramineae, the allocationof the two glucan synthases to two different membrane fractionsis not possible. Key words: Golgi apparatus, Glucan synthases, Plasma membrane, Sugar cane cells