Kinetics of Mating in Physarum polycephalum

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Abstract
Plasmodium formation by mating was studied in cultures containing equal numbers of mating-compatible amoebae. A period of amoebal multiplication always preceded plasmodium formation. When the inoculum varied from a total of 3 .times. 103-1.6 .times. 105 cells/culture, plasmodium formation commenced when the total number of cells reached about 5 .times. 105 per culture. When the inoculum included an excess of a 3rd strain of amoebae that is unable to mate with the first 2, mating commenced when the total number of matable cells reached only 1 .times. 105/culture. This effect of the 3rd strain of amoebae was not brought about by their consumption of the bacteria used as food, since directly limiting the number of food bacteria did not cause earlier mating. When amoebae of the 3rd strain were separated from the mating cells by paired 0.2 .mu.m Nuclepore filters, premature mating still occurred. Thus, as is the case with asexual plasmodium formation, one or more extracellular factors appear to influence the time of onset of mating.