Allocyclic Regions and Banding Patterns in the Chromosomes of Najas Marina

Seven spontaneous allocyclic regions have been observed in the prophase and prometaphase chromosomes of the first pollen mitosis in race B of Najas marina. Morphologically the allocyclic regions were similar to the cold-induced H-segments observed in some organisms. C-bands were shown to correspond to the allocyclic regions. In addition, after use of the C-banding method there were paired dots in the centromeric regions of all the six chromosomes. With quinacrine mustard staining the allocyclic regions were not differentiated in any way. However, with phase contrast microscope these regions were sometimes visible as unstained gaps when acetic acid treated chromosomes were stained with Feulgen. There were no allocyclic regions in B chromosomes. After C-banding two dark dots were also visible in the centromeric region of the B chromosome. The rest of this chromosome was stained as pale as the interband regions in A chromosomes. In this respect, the B chromosomes behave like facultative heterochromatin. It was proposed that both the formation of allolyclic regions and C-bands depend on the presence of a special protein component in these chromosome regions.