Pseudopod formation and membrane production during prey capture by a heliozoon (feeding by Actinophrys, II)

Abstract

Two phases of prey capture by the heliozoon Actinophrys sol are documented by electron microscopy. The phases are those of prey adhesion to the predator and enclosure of the prey by the predator. Adherence is brought about by numerous small pieces of adhesive membrane produced by the predator at the site of prey contact. Some of the heliozoan extrusomes expel their contents at this time, but the significance of this event is unclear. Enclosure of the prey is effected by a funnelshaped pseudopodium. This is drawn over the prey by the action of the leading margin. The ultrastructural appearance of the cytoplasm of the leading margin differs from the rest of the cell, being homogeneous and finely filamentous. Both force and traction for the progression of the pseudopod are generated primarily at the tip. During the development of the funnel-pseudopod, extrusomes expand and fuse with each other and with the plasma membrane. Their investing membrane is thereby made available as food vacuole membrane.

Insights into the evolution of heliozoa (Protozoa, Sarcodina) as provided by ultrastructural studies on a new species of flagellate from the genus Pteridomonas

“…as food, with or without Bacillus mycoides as a substrate for attachment. Light-microscopy was carried out using the procedure described elsewhere (Patterson, 1982). For electron-microscopy cells were fixed in 2.5% (w/v) glutaraldehyde with 1% (w/v) osmium tetroxide in 50 mM/1.…”

“…The taxon contains two genera (Actinophrys and Actinosphaerium), both of which have been fairly well studied. Some recent accounts of the biology of these organisms are given by Hausmann & Patterson (1982), Mignot (1979Mignot ( , 1980a, Patterson (1979), Patterson & Hausmann (1981), Patterson & Thompson (1981) and Suzaki, Shigenaka, Watanabe & Toyohara (1980). The constitution of this taxon is discussed by Patterson (1985).…”

“…However, when viewed with the electron-microscope, several distinct patterns of cytoplasmic organization are encountered (for data see Bardele, 1972Bardele, , 1975Bardele, , 1977Cachon & Cachon, 1978Febvre-Chevalier, 1973Hausmann & Patterson, 1982;Jones, 1976;Mignot, 1979Mignot, , 1980aPatterson, 1979;Patterson & Hausmann, 1981;Patterson & Thompson, 1981;Rieder, 1979;Smith & Patterson, 1985, Suzaki et al, 1980Tihey & Porter, 1965). Differences between patterns relate to the arrangement of microtubules in axonemes, sites of axonemal nucleation, types of extrusomes present, appearance of mitochondrial cristae, location of dictyosomes, presence of cysts and nature of cyst wall, presence of sexuality, patterns of nuclear division, presence of flagellated stages in the life cycle and the nature of additional cytoplasmic inclusions.…”

Food capture and adhesion by the heliozoonActinophrys sol

“…Various types of extrusomes are present in protozoan cells (Hausmann 1978, Kugrens et al 1994, Hausmann and Hfilsmann 1996. Extrusomes are membrane-bound vesicles located in dose proximity to the plasma membrane and have various kinds of defensive or offensive functions.…”

The Ultrastructure of Contractile Tubules in the Heliozoon Actinophrys sol and Their Possible Involvement in Rapid Axopodial Contraction

“…In Echinosphaerium , the driving force for axopodial contraction is considered to be conformational changes in a bundle of contractile tubules (formerly called X‐bodies: Shigenaka and Kaneda 1979), which are located alongside the axonemal microtubules (Ando and Shigenaka 1989; Suzaki et al 1980, 1994). The smaller, single‐nucleated heliozoon Actinophrys also uses axopodia when it captures prey organisms (Hausmann and Patterson 1982; Ockleford and Tucker 1973; Patterson and Hausmann 1981; Sakaguchi et al 1997, 1998, 2001). Similar axopodial contraction has been reported to occur in this species (Ockleford and Tucker 1973).…”