CYTOLOGICAL STUDY ON TRIPLOID RYE WITH FOUR ACCESSORY CHROMOSOMES

Abstract

In the triploid rye plant with four accessory chromosomes, the cytological investigation was made and the behaviour of accessory chromosomes was compared with one in the original diploids. The results are summarized as follows.1. The chromosomes in the triploid showed a relatively higher degee of pairing at mataphase I, viz., the modal configuration was found in 4III+3II+3I+BIV, and 5III+2II+2I+BIV and 3III+4II+4I+BIV followed. The association of normal chromosomes may not be influenced by the presence of accessory chromosomes. At stages between anaphase I and tetrad formation, various abnormalities were observed. In almost all of the cells the lagging of the chromosomes and their abnormal distribution were seen at anaphase I and II, and tetrad and pentad with micronuclei were most frequently observed.2. The metaphase I configurations of accessory chromosomes in the triploid were the same as one in the original diploids, but their frequencies differed. The frequency of multivalents, such as quadrivalent and trivalent, was lower than that in the diploid. This indicates that the association of accessory chromosomes may be reduced by the increase of normal chromosome complements.3. In the disjunction of accessory chromosomes, various abnormalities, such as the laggards, the abnormal distribution and the occurrence of tetrad with micronuclei, in the triploid were more frequent than those in the diploids. This fact indicates that the disjunction of accessory chromosomes may be disturbed by the increase of normal chromosome complements.