AN APPRAISAL OF THE DEVELOPMENTAL IMPORTANCE OF POLYAMINE CHANGES IN EARLY XENOPUS-EMBRYOS

The biological importance of the various changes in polyamine metaboli sm that occur during early Xenopus development have been investigated. Incubation of embryos in high salt medium was observed to cause a pre cocious fall in ornithine decarboxylase activity without affecting dev elopment. Similarly, inhibiting ornithine decarboxylase activity with specific inhibitors did not affect development. Injecting spermidine, within physiologically relevant limits, caused a dose-dependant inhibi tion of mitotic divisions in the injected blastomere. Increasing the i ntracellular putrescine did not affect cell division or development. C o-injection of both spermidine and putrescine, so that the original mo lar ratio of these two polyamines was conserved, abrogated the inhibit ion of cell division observed when spermidine was injected alone. Ther efore, in Xenopus embryos the intracellular spermidine concentration m ust be retained within certain limits relative to that of putrescine t o allow normal development.