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RNA accumulation in Chlamydomonas reinhardtii during the course of wall regeneration in protoplasts prepared by treatment of vegetative cells with autolysin was studied. In vitro translation of poly(A)+ RNA isolated from wall-regenerating cells indicated that cell wall removal induced the accumulation of several large RNA transcripts. Some of these induced RNAs were enriched following oligo(dG)-cellulose chromatography (referred to as cytosine-rich). The induced and cytosine-rich poly(A)+ RNAs potentially code for hydroxyproline-rich cell wall glycoproteins (HRGPs). Immunoprecipitation of in vitro translated products with an antiserum against a deglycosylated wall fraction (2BII) confirmed that these RNAs contained species involved in cell wall biosynthesis.

Gametes of the unicellular green alga Chlamydomonas reinhardii recognize and adhere to cells of the opposite mating type by flagellar contact. Adhesion between these specialized organelles signals a rapid series of mating events which result in gamete fusion. The sequence of morphological changes (flagellar tip activation, cell wall loss, and mating structure elongation), which occur as a consequence of the sexual signalling, have been characterized. The signalling mechanisms have, however, not been defined. Calcium is known to be involved during fertilization of animal species. Increased intracellular free calcium, which can be achieved either by calcium influx or by mobilization of ions from intracellular stores, has been observed during activation of both eggs and sperm. A recent report by Bloodgood & Levin that gametes of C. reinhardii preloaded with 45Ca showed a transient increase in Ca efflux following mating, suggests that intracellular Ca redistribution may also accompany mating in this algal species. We have used X-ray microanalysis to analyze the subcellular distribution of bound calcium during mating in Chlamydomonas reinhardii. X-ray maps reveal that calcium is sequestered in discrete granules within the gamete cell body prior to mating and that during activation and cell fusion, calcium is diffuse throughout the cell. This suggests the possibility that calcium serves as a second messenger in this species.