299:	The Golgi apparatus of the scaly green flagellate Scherffelia dubia: Uncoupling of glycoprotein and polysaccharide synthesis during flagellar regeneration.

Authors:	Becker, Burkhard(A)Perasso, Lara(B)Grunow, Andrea(A)Brüntrup, Ines, M.(A)Bölinger, Barbara(A)Melkonian, Michael(A)
Affiliations:	(A): Botanical Institute, University of Cologne (B): Plant Cell Biology Group, Australian National University
Presenter:	Becker, Burkhard , bbecker@novell.biolan.uni-koeln.de

The flagella of the green alga Scherffelia dubia are covered by scales which consist of acidic polysaccharides and glycoproteins. Experimental deflagellation results in the regeneration of flagella complete with scales. During flagellar regeneration scales are newly synthesized in the Golgi apparatus, exocytosed and deposited on the growing flagella. Flagellar regeneration is dependent upon protein synthesis and N-glycosylation, as it is blocked by cycloheximide and partially inhibited by tunicamycin. Metabolic labelling with 35S methionine/cysteine demonstrated that scale-associated proteins were not newly synthesized during flagellar regeneration suggesting that the proteins deposited on regenerating flagella were drawn from a pool. Immunoelectron microscopy using a monospecific antibody directed against a scale-associated protein of 126 kDA (SAP126) revealed that SAP126 was largely confined to the plasma membrane, scale-reticulum and trans-Golgi cisternae both before deflagellation and during flagellar regeneration. Quantitative immunoelectron microscopy identified the pool of SAP126 to be primarily located at the plasma membrane. Since SAP126 was sequestered during flagellar regeneration into secretory vesicles together with newly synthesized scales, we conclude that the persistent presence of SAP126 in the trans-Golgi cisternae during scale biogenesis requires retrograde transport of the protein from the plasma membrane to the Golgi apparatus.