CYTOKININ INDUCES THE DEVELOPMENTALLY RESTRICTED SYNTHESIS OF AN EXTRACELLULAR PROTEIN IN PHYSCOMITRELLA-PATENS

Early development of the moss Physcomitrella patens follows a simple c ourse leading to the formation of a filamentous protonema containing o nly two cell-types, chloronema and caulonema. The addition of the horm one cytokinin leads to the induction of multicellular buds from such p rotonema. The spectrum of extracellular proteins (ECPs) synthesized by P. patens has been investigated at defined stages of development and under defined hormone treatments. It is found that in contrast to the limited changes in intracellular protein synthesis detectable, in the extracellular environment major and specific changes in the patterns o f proteins synthesized occur. For example, the presence of caulonema c ells is characterized by the synthesis of a 25 kDa ECP whereas early c hloronema differentiation is distinguished by the presence of a 38 kDa ECP. The analysis of the pattern of ECPs synthesized by developmental mutants altered in bud formation, and in response to cytokinin in tun icamycin treated protonema (in which bud induction is blocked) indicat e that the synthesis of a 14 kDa ECP is specifically induced by cytoki nin. This protein represents a novel cytokinin-induced ECP. These data show that the differentiation of particular cell types in plants is a ssociated with the synthesis of particular ECPs, and suggest that horm ones which induce specific morphogenic events may do so via the synthe sis of specific ECPs.