KOZO NISHIKAWA
Faculty of Agriculture, Gifu University, Gifu, Japan
A highly contracted and rod like metaphase chromosome is unfavorable for micro-spectrophotometrical measurement of DNA content. Instead, the micronucleus in pollen tetrads of aneuploids such as the monosomics provides an optically favorable material, whose DNA content must be equivalent to that of the specific univalent from which the micronucleus is derived.
Anthers of seven monosomics (1D-7D) of Chinese Spring were fixed with Carnoy's fluid and sectioned longitudinally ten microns thick. The procedure elaborated by SIBATANI and NAORA (1952) was followed for Feulgen staining after hydrolysis with N-HCl at 60C for five minutes. Extinction of stained nuclei at the wave length of 550mmicro was measured by NAORA's method (NAORA 1955) using an Olympus MSP A-IV.
The table below shows the relative DNA content of individual chromosomes and their length reported by SEARS (1954). It is apparent that the DNA content of the individual chromosomes is almost proportional to their length with the exception of chromosome 5D. Chromosome 5D contained a much larger amount of DNA than could be expected from its length. No reasonable explanation for this finding can be given at present.
DNA content (arbitrary unit) and length of seven chromosomes belonging to the D genome of common wheat :
(Received June 26, 1967)