Structure and Activity of Water Expulsion Vacuoles in
Monoblepharella sp. Zoospores
Fungal Genetics and Biology (1997) In Review.
John P. Shields* and David Porter
*Plant Pathology Department and Dept. of Botany, Miller Plant
Science Bldg., University of Georgia, Athens, GA 30602-7274 USA
Water expulsion vacuole (WEV) activity in Monoblepahrella sp.
zoospores cycled every 6 sec and was confined to an anterior "clear zone"
in zoospores. Large expulsion vacuoles (EVs) formed through the fusion of
smaller accumulation vacuoles and vesicles. The EV eventually fused with
the spore's plasma membrane and expelled its contents to the exterior
while collapsing. Coated lobes formed as the EV collapsed and broke into
clathrin-coated vesicles. Immunoelectron microscopy labeling of the
zoospore surface indicated membrane differentiation. Immunofluorescence
localization of the cytoskeleton revealed that microtubules (MTs) formed a
basket extending from the kinetosomal region and ending short of the clear
zone. Actin localized throughout the zoospore with actin plaques
concentrated along the spore periphery. MT depolymerization had no
visible effect on WEV activity, while microfilament depolymerization
resulted in WEV activity cessation and eventual spore lysis. These
results suggested that actin was involved with WEV function, while MTs
were not directly involved.