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Experimentally induced aberrations in the pattern of differentiation in the cellular slime mould Dictyostelium discoideum.

This paper describes a set of perturbatory experiments designed to elucidate aspects of the mechanism by which the normal pattern of differentiation is specified. Experiments are described which investigate the alterations in development seen in aqueous environments, with changes in humidity and with the introduction of permeable and impermeable barriers. The following results are reported: (i) The pattern of differentiation and the various morphologies of fruiting bodies formed when cell masses are placed in or on drops of buffer. (ii) The alteration of the ratio of cell types formed in aqueous environments in the presence of urethane, mercaptoethanol or EDTA. (iii) Humidity dependent changes in polarity and the increase of the number of developmental axes with humidity. (iv) The formation of two developmental axes in cell masses bisected by impermeable barriers and a special case of bisection which induces the whole cell mass to form spores. (v) The induction of all of any of a cell mass enclosed in a ‘cellulose’ tube to form a tissue ultrastructurally demonstrable to be the same as that of stalk. These results are discussed in relationship to the work of other authors and the problem of the specification of the patterns of differentiation in the slime moulds. The results are presented in support of a model proposed previously by the author in which the pattern of the two differentiated cell types is inherent in the morphogenetic changes of culmination, and essential requirements of such a model are correlated with these observations.