An analysis of protein and RNA synthesis during encystment and outgrowth (germination) of Blastocladiella zoospores

Abstract

Motile zoospores of Blastocladiella emersonii encyst and produce a primary rhizoid in a germination process requiring less than one hour. The events of encystment do not require either RNA or protein synthesis. Subsequent cellular differentiation is dependent upon protein synthesis which takes place upon preformed messenger RNA and ribosomes stored in the zoospore. During the early stages of zoospore germination the nuclear cap containing only monoribosomes disperses and polysomes accumulate rapidly reaching 50% of the total ribonucleoprotein by 20 min and 70% after 60 min. This increase in protein synthesis is associated with a marked increase in the rate of translation, apparently a consequence of the decline of a translation inhibitor. Preferential synthesis of ribosomes during the first 80 min of germination increases the cellular RNA/protein ratio to a value characteristic of rapidly growing cells. Although ribosome and messenger RNA synthesis begin soon after encystment, they do not become essential for continued growth and development until after production of the first rhizoid at 45 min.