THE MECHANISM OF SOMATIC ASSOCIATION IN COMMON WHEAT, TRITICUM AESTIVUM L. II. DIFFERENTIAL AFFINITY FOR COLCHICINE OF SPINDLE MICROTUBULES OF PLANTS HAVING DIFFERENT DOSES OF THE SOMATIC-ASSOCIATION SUPPRESSOR

Abstract

HE homologous chromosomes of common wheat, Triticum crestiuum L., are Tassociated in somatic cells (FELDMAN, MELLO-SAMPAYO and SEARS 1966). This somatic association is regulated by a gene system located on the chromosomes of homoeologous group 5, i.e., chromosomes 5A, 5B, and 5D, (FELDMAN 1966(FELDMAN , 1968). The long arm of chromosome 5B (5BL) carries a gene which SUPpresses somatic association and thus tends to cause random distribution of homologues in the somatic nucleus. On the other hand, the short arm of chromosome 5B (5BS) and the long and short arms of chromosomes 5A and 5D carry genes which promote somatic association. The effect of the somatic-association promoters is opposite to that of the somatic-association suppressor. Thus in common wheat there is a balance between the suppressor and the several promoters which determines the degree of somatic association that occurs.Studies on the effect of the somatic-association genes in aneuploid wheat plants having different doses of chromosomes 5B, 5D, and 5A have shown that this balance can be shifted in either direction (FELDMAN 1966(FELDMAN , 1968) by increasing the

Homologous chromosome pairing

“…This situation is said to prevail in the presence of the gene on chromosome 5B which is associated with normal bivalent pairing in wheat, but not in its absence (where multivalent pairing is expected at meiosis). It has also been reported that this gene on chromosome 5B alters spindle tubulin (Avivi, Feldman & Bushuk 1970). Such findings seem consistent with the interpretation that each of the three wheat genomes may have a specific centromere relationship to a special spindle or spindle region of its own and that a normal chromosome 5B gene is needed for the maintenance of the relation ship.…”