| Genome differentiation, nucleolar organizers and RNA
synthesis in wheat H. K. JAIN, M. P. SINGH and R. S. UTKHEDE Division of Genetics, Indian Agricultural Research Institute, New Delhi, India Four of the 21 pairs of chromosomes in Triticum aestivum are known to have a nucleolar organizing locus (CROSBY 1957). The relative contribution of each of these four loci to RNA synthesis has been studied in the root tip cells by observing the incorporation of tritium labelled uridine. The incorporation has been analysed in two types of materials. It has been studied in the first place in the four ditelosomes for the long arm of chromosomes 1A, 1B, 6B and 5D, as well as in the variety Chinese Spring, from which they have been developed by SEARS (1952a and b). The missing short arm of one of the four chromosomes in the above ditelosomes is known to carry the nucleolar organizer. The incorporation of the tritium labelled uridine has also been observed in root tip cells of four diploid, tetraploid and hexaploid wheat species. The method of incorporation of the labelled precursor and of the preparation of the autoradiographs has been described earlier by one of us for another material (JAIN 1966). A large number of interphase cells were scored (Fig. 1) for grain count in several slides of each of the lines and varieties, following identical incorporation treatments. The observations on mean number of silver grains per cell (estimated by pooling of the observations on different slides of a line) are presented in Tables 1 and 2 for the two types of materials. |
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