Chromosomal rearrangements in Plantago insularis Eastw.

Abstract

Seeds of Plantago insularis Eastw. which were irradiated with gamma rays yielded 37–67% semi-sterile plants. Twenty-four out of sixty-four of these plants were heterozygous for one or more chromosomal rearrangements. Twothirds of these were translocations, and one-third were inversions. Homozygous lines for four translocations were established. The karyotypes of these provide chromosome markers either at pachynema or in mitotic divisions, or both.

Breakage positions were usually located within hetrochromatic segments or at the ends of heterochromatic regions (72.6% of all breaks), and half of all breaks occurred at the juncture of the centromere with the proximal heterochromatin. The consequences of proximal breakage were non-random, in that 93% of such breaks resulted in translocations and only 7% in inversions, whereas more than half of breaks in non-centromeric regions became involved in inversions.

The individual chromosomes differed in the types of breakage and of aberrations produced, and these differences appeared correlated with length ratios of heterochromatic segments flanking the centromeres.