The Israeli Journal of Aquaculture - Bamidgeh 55(4), 2003
The 7th Annual Dan Popper Symposium


BREFELDIN A INFLUENCES CELL-WALL PRODUCTION IN THE
RED MICROALGA PORPHYRIDIUM SP.THROUGH ITS EFFECT
ON THE GOLGI APPARATUS


Marina Keidan¹,², Y. Weinstein³ and S. (Malis) Arad¹*

1 Institute for Applied Biosciences, Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel

2 Department of Life Sciences, Faculty of Health Sciences Ben Gurion University of the Negev, Beer Sheva, Israel

3 Department of Microbiology and Immunology, Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel


Abstract

The cells of red microalga Porphyridium sp.are encapsulated within a complex sulfated polysaccharide, the external part of which dissolves continuously in the medium. This cell-wall polysaccharide is composed of 10 different sugars and contains non-covalently bound cell-wall proteins. The Golgi apparatus of all eukaryotic cells is the site of glycosylation of proteins and biosynthesis of complex polysaccharides. In some mammalian cells the Golgi apparatus is involved in sulfation of proteoglycans. In this study, we investigated the effect of Brefeldin A on cell-wall synthesis in Porphyridium sp. Brefeldin A is a fungal metabolite that disassembles the Golgi apparatus into a tubular network and causes dissociation of coatomer proteins from the Golgi membranes. Brefeldin A acts on the ADP-ribosylation factor (ARF), the small G protein that plays a key role in vesicular transport processes. Treatment with Brefeldin A had the following effects on the Porphyridium sp.
Cell growth was inhibited.
Polysaccharide production was reduced.
Golgi structure was disrupted (as shown by electron microscopy).
Incorporation of 14C and 35S into the polysaccharide was reduced (pulse-chase experiments).
ARF mRNA transcription ceased (Northern blot analysis).
ARF level was reduced (Western blot analysis).
These findings suggest that Brefeldin A affects polysaccharide biosynthesis and secretion in Porphyridium sp. cells through its action on the structure of the Golgi apparatus and through the ARF protein.


*email: Arad@bgumail.bgu.ac.il

home