Polyamine Biosynthetic Enzymes intheCell Cycle ofChlorellal

During thelife cycle ofChlorella vulgaris Beijerinck varvulgaris fa. vulgaris growing synchronously, thespecific activity ofornithine decarboxylase peaked atthe2ndhourofthecycle, whereas that ofarginine decarboxylase changed only slightly, increasing towards theendofthe cycle. Theendogenous level ofputrescine andspermidine onapercell basis increased gradually uptothe8thhourofthecycle, anddeclined thereafter. Thus, thepeakofornithine decarboxylase activity andthe polyamine increase preceded bothDNA replication (which tookplace between the6thand8thhours ofthecycle) andautospore release (which started atthe8thhour). A 2-fold increase inthelight intensity caused doubling oftheDNA content, resulting indoubling ofthenumber of autospores permother cell. Italso brought about a2-fold increase inthe specific activity ofornithine decarboxylase andpolyamine content, the peaks being atthesamehourofthecycle underhigh andlowlight intensities. Theincrease incell numberandpolyamine content ina Chlorella culture grownunderhigh light intensity wasinhibited byadifluoromethyl ornithine, aspecific inhibitor ofornithine decarboxylase, this inhibition being partially reversed byputrescine. Itissuggested that inC.vulgaris thesequence ofevents which relates polyamine biosynthesis tocell division isasfollows: increased ornithine decarboxylase activity, accumulation ofpolyamines, DNA replication, andautospore release.