Induction of synchronous encystment in a hypotrichous ciliate, Histriculus sp

Temporal suspension of excystment by salt solution in the ciliate, Histriculus cavicola (Kahl, 1935) (Ciliophora: Stichotrichia)

Cysts were incubated in excystment medium (EM) for varying periods and then transferred to salt solutions or to 5 μg/ml cycloheximide (CH). When the transfer was to salt solutions, almost no cell excysted within 24 h after initiation of incubation in EM if the incubation was shorter than 30 min, but the proportion of excysted cells increased with increasing incubation time longer than 40 min. When the transfer was to CH, no cell attained stage 2 of excystment after incubation in EM shorter than 30 min but normal excystment ensued after an incubation longer than 70 min. If incubation in EM was between the above mentioned periods, some cells attained stage 3 but never excysted. Kinetosome formation occurred after incubating cysts for 30 min in EM, regardless of the presence or absence of CH. Formed kinetosomes, however, disappeared if cysts were maintained in salt solutions for 210 min or in CH for 240 min. These results indicate that: 1) excystment requires protein synthesis and incubation of cysts in EM longer than 30 min, 2) kinetosome formation does not need protein synthesis and does not necessarily direct cysts to complete excystment, and 3) maintenance of new kinetosomes requires continuation of the excystment process.

Reversibility of encystment in the ciliate, Histriculus cavicola (kahl, 1935) (ciliophora: stichotrichia)

An early phase of encystment of the ciliate, Histriculus cavicola is subdivided into 5 stages, stages A to E. Resorption of feeding organelles, undulating membranes (UM) and the adorai zone of membranelles (AZM) start from stage B. In stage E cells, resorption of UM is completed and that of the AZM reaches to the level of anterior end of left marginal cirral row from its posterior end. When stage A cells are transferred in culture medium with or without food organisms, or in normal or 10 times concentrated Osterhout's solutions with food, most cells do not encyst. More than half of stage C cells do not encyst at 20°C after transfer in culture medium. All stage E cells encyst, irrespective of the medium or of the presence or -the absence of food into which they are transferred. About half of stage A cells and all stage B to E cells contain ectocyst precursors. Our results indicate that initiation of ectocyst precursor formation does not necessarily direct the cells to encyst but cells in stage E are determined to encyst.