Growth rate and haploidization ofAspergillus nigeron medium containingp-fluorophenylalanine

The comparison of the dry weight of thin layer haploid and diploid colonies of A. niger on complete medium and complete medium supplemented with p -fluoro-phenylalanine led to the conclusion that there is a difference in growth rates of hyphae under these different conditions. 2. The growth curves of the same strains on both media were established. On complete medium, haploids and diploid show a growth rate increasing linearly for about 20 h after germination and reaching a maximum which is then maintained. On p -fluorophenylalanine, the haploids show a similar curve, although the maximum growth rate reached and maintained is about half that on complete medium; for the diploid, however, the maximum is less than the corresponding one in the haploid and, once this maximum has been reached, the growth rate goes down linearly to a very low value which is then maintained. 3. The cytological study of the hyphal tip cell showed, in the presence of the amino acid analogue, a reduction of the mean size of the diploid nuclei together with an increase of the number of nuclear fragments. This explains the growth rates observed and is accepted as a confirmation that p -fluorophenylalanine, by its action on the mitosis, favours chromosome losses which lead finally to the production of haploid nuclei.