Amino acid pools in developing Chlamydomonas reinhardtii: vegetative cells, gametes, and mature zygotes

Abstract

Free amino acid pools were examined for cultures of vegetative cells, gametes, and mature zygotes of the unicellular green alga Chlamydomonas reinhardtii (Dangeard). The total pool of amino acids found in premature gametes of strains 137c+ (10.0 pmol∙μg protein−1) and 137c− (10.8 pmol∙μg protein−1) decreased to levels about half that seen in vegetative 137c− cells (19.8 pmol∙μg protein−1). Following light activation, amino acid pools in these gametes increased to 18.7 pmol∙μg protein−1 in 137c+ cells and 20.0 pmol∙μg protein−1 in 137c− cells. With the exception of cystine, individual amino acid pools in these cells had increased once more to levels similar to those seen in vegetative cells grown in liquid medium. Levels of cystine remained one to two orders of magnitude lower than that seen in vegetative cells. Mature 137c + and 137c− gametes mixed in solutions of either 2 mM cystine or 2 mM cysteine (half-cystine) suffered a 52–64% reduction, respectively, in the number of vis-à-vis conjugative pairs formed. This suggests that pools of endogenous cystine may play a role in the onset of mating. In zygotes levels of all amino acid pools, except histidine, were depressed; levels of cystine, valine, and phenylalanine were nondetectable in these cells.Key words: Chlamydomonas reinhardtii, amino acid pools, gametes, zygotes, cystine.