ENCYSTMENT STAGES OF DICTYOSTELIUM

Abstract

Of the 2 stages described, microcysts are unicellular and represent a resting stage in the vegetative phase. Macrocysts are multi-cellular and arise through a morphogenetic process possibly alternative to normal sorocarp formation. Myxamoebae aggregate into typical but diminutive pseudo-plasmodia which subdivide into rounded cell masses encased in cellulose walls. The myxamoebae comprising the macrocyst concurrently differentiate into polyhedral cells with highly refractive membranes. After 10 to 14 days these so-called endocytes disappear, and the macrocyst assumes an acellular homogeneous appearance. With further aging the protoplasmic content shrinks away from the cellulose wall. Such macrocysts retain their viability for protracted periods and under favorable conditions of temperature and substrata can germinate to release amoeboid cells which reinitiate the vegetative stage. Apparently, all members of the Acrasieae are able to produce microcysts, but macrocysts have been observed only in D. minutum and in occasional isolates of P. mucoroides.