Spore-cell differentiation in monolayers in vitro of two sporagenous mutants of Dictyostelium discoideum, HM18 and HM15, is markedly inhibited by relatively low concentrations of the exogenous lectins, Concanavalin A (ConA) and wheat germ agglutinin (WGA) and by somewhat higher concentrations of the endogenous lectin, discoidin. The selective inhibition of spore cell formation by ConA occurs toward the end of the differentiation process, as shown by studies involving the addition or removal of ConA at various times during the period of differentiation. In addition, ConA has no deleterious effect on the expression of the pre-spore cell specific enzyme, UDP-galactosyl transferase. It is likely, therefore, that the maturation of pre-spore cells into spore cells is the most sensitive locus of lectin inhibition. At higher concentrations of WGA and ConA, both stalk- and spore-cell formation are inhibited, but increased concentrations of discoidin do not have this effect.

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