THE STRUCTURAL AND FUNCTIONAL ANALYSIS OF THE SURFACE APPARATUS IN FOUR SPECIES OF SARCOCYSTIS
(SPOROZOA, APICOMPLEXA)
A. I. Radchenko, T. V. Beyer
Institute of Cytology RAS, St. Petersburg, Russia;
e-mail: sarcocystis@mail.ru
The comparable ultrastructural analysis of the sarcocyst surface apparatus (SSA) was made for four species of
Sarcocystis: Sarcocystis muris, S.fusiformis, S. medusiformis, and Sarcocystis sp. from buffalo heart muscles. In
all these species, SSA contains a surface membrane, overmembrane complex with glycocalyx, and submembrane complex made of two
glycoprotein SSA primembrane layers. SSA makes numerous primary vesicle-like protrusions and pits in between. Some vesicles
containing two layers, PM1 and PM2, are pinching off from the totally formed protrusions. Then these vesicles are directed into
infected host cell to participate in its degradation. In the SSA pits neither over-, nor submembrane complex is present, the pits
being made of the surface membrane only. It is important that fibrillar structures penetrate through the SSA membrane into pits
from the host cell. Besides, SSA forms secondary protrusions with different structures in various species of Sarcocystis. They
increase the sarcocyst surface and transport different substances along intermediate filaments from the SSA pits membrane to the
sarcocyst body. At the same time, deep invaginations are found in the SSA of old sarcocysts. We thought that these structures
increased the sarcocyst surface and thus promote to intensify metabolism. This study-defined presence of membranous vesicles in
secondary protrusions. According to their structure and localization, the membranous vesicles may be involved in the building of
the sarcocyst surface membrane.
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