Meier R, Lefort-Tran M, Pouphile M, Reisser W, Wiessner W
J Cell Sci. 1984 Oct;71:121-40. doi: 10.1242/jcs.71.1.121.
In the endosymbiotic unit of Paramecium bursaria (Ciliata) and Chlorella sp. (Chlorophyceae) algae are enclosed individually in perialgal vacuoles, which do not show acid phosphatase activity and thus differ from digestive vacuoles. Both types of vacuoles have been studied by freeze-fracture. Perialgal vacuoles are nearly spherical; their membrane always fits tightly to the algal surface. The vacuole size and shape do not vary much. During division of the algal cell into four autospores the vacuole diameter only doubles. After autospore formation the vacuole invaginates around the algal daughter cells and divides. Newly formed perialgal vacuoles remain in intimate contact and exhibit characteristic attachment zones before final separation. The two fracture faces of perialgal vacuole membranes are homogeneously covered with intramembranous particles (IMPs) but rarely show signs of vesicles pinching off or fusing with the membrane, except during vacuole division. The P-faces bear more IMPs (3164 +/- 625 IMP/micron 2) than the E-faces (654 +/- 208 IMP/micron 2). The range of IMP density on both faces is enormous, suggesting that the membrane is not static. Membrane changes are supposed to occur simultaneously with the enlargement of the vacuole and to be caused by fusion with cytoplasmic vesicles, as the fractured necks on vacuole membranes may indicate. Digestive vacuoles in P. bursaria show significant variations in size, shape, membrane topography and IMP density, as well as signs of endocytic activity. Different vacuole populations are present in P. bursaria according to different feeding conditions: ciliates fed for a long time have small vacuoles with few IMPs (322 +/- 198 IMP/micron 2 on the E-faces, 1438 +/- 458 IMP/micron 2 on the P-faces), which are probably condensed digestive vacuoles, whereas organisms fed for a short time have larger vacuoles with highly particulate faces (680 +/- 282 IMP/micron 2 on the E-faces, 2701 +/- 503 IMP/micron 2 on the P-faces) and thus are supposed to be older vacuoles. The digestive vacuole membrane changes continuously. Compared to digestive vacuoles perialgal vacuoles are characterized by small size combined with high IMP density on the two fracture faces. Their IMP densities resemble those of old digestive vacuole membranes. However, it would be premature to conclude that membranes of perialgal and old digestive vacuoles are identical. Membranes of old digestive vacuoles are mainly derived from lysosomal material, which presumably does not contribute to the formation of perialgal vacuole membranes as is indicated by the small vacuole diameter; fusion with lysosomes would considerably enlarge it.(ABSTRACT TRUNCATED AT 400 WORDS)
在草履虫（纤毛虫纲）和小球藻（绿藻纲）形成的内共生单元中，藻类被分别包裹在藻周液泡中，这些液泡不显示酸性磷酸酶活性，因此与消化液泡不同。这两种液泡都已通过冷冻断裂法进行了研究。藻周液泡近似球形；其膜总是紧密贴合藻类表面。液泡的大小和形状变化不大。在藻类细胞分裂成四个游动孢子的过程中，液泡直径仅翻倍。游动孢子形成后，液泡围绕藻类子细胞内陷并分裂。新形成的藻周液泡在最终分离前保持紧密接触并呈现出特征性的附着区域。藻周液泡膜的两个断裂面均匀地覆盖着膜内颗粒（IMPs），但除了在液泡分裂期间，很少有小泡从膜上 pinched off 或与膜融合的迹象。P面的IMPs（3164±625个IMPs/微米²）比E面（654±208个IMPs/微米²）多。两个面上IMPs密度的范围很大，这表明膜不是静态的。膜的变化应该与液泡的扩大同时发生，并且可能是由与细胞质小泡的融合引起的，正如液泡膜上断裂的颈部所表明的那样。草履虫中的消化液泡在大小、形状、膜拓扑结构和IMPs密度上有显著变化，以及内吞活动的迹象。根据不同的摄食条件，草履虫中存在不同的液泡群体：长期摄食的纤毛虫有小液泡，IMPs较少（E面为322±198个IMPs/微米²，P面为1438±458个IMPs/微米²），这些可能是浓缩的消化液泡，而短期摄食的生物体有较大的液泡，其表面有高度颗粒化（E面为680±282个IMPs/微米²，P面为2701±503个IMPs/微米²），因此被认为是较老的液泡。消化液泡膜不断变化。与消化液泡相比，藻周液泡的特征是体积小，且两个断裂面上的IMPs密度高。它们的IMPs密度类似于老消化液泡膜的密度。然而，得出藻周液泡膜和老消化液泡膜相同的结论还为时过早。老消化液泡膜主要来源于溶酶体物质，而液泡直径较小表明溶酶体物质大概对藻周液泡膜的形成没有贡献；与溶酶体融合会使其显著增大。（摘要截短至400字） 注：原文中“pinched off”未翻译完整，推测可能是“掐断、脱离”之类意思，这里保留英文以便理解。
