IDENTIFICATION AND LOCALIZATION OF A TRANSLOCATION IN PISUM
CHROMOSOMES BY THE C-BANDING TECHNIQUE
Wolff, G. Institute of Genetics, University of Bonn
Federal Republic of Germany
Gottschalk's mutant collection in Bonn initially included, among
others, 120 translocation genotypes. They originated in 1954 from
radiation experiments with cv 'Dippes Gelbe Viktoria'. The transloca-
tion lines were selected by analyzing pollen sterility. From these 120
genotypes only 30 are now still available.
In the early work, eight translocation genotypes were investigated
by examining the mitotic chromosomes of the root tips. Homogeneously
stained chromosomes were measured and the values of the mutant lines
were compared with those of the controls. The deviations in total
length and arm indices were the basis of these investigations (2, 6).
Though the participating chromosomes could be identified, the exact
localization of the exchange was impossible.
The development of the banding techniques in the early seventies
seemed to provide a promising tool for overcoming some of the technical
problems. The C-banding method is especially useful for identifying the
heterochromatic regions in plant chromosomes. However, this technique
proved difficult in Pisum. Attempts in our institute succeeded only in
characterizing chromosomes 4 and 7 (nomenclature according to Blixt
[1]). The banding pattern corresponded to that published by Lamm in
1978 (3). Because of the difficulties, the investigations in our insti-
tute were discontinued. Lamm published some further results on banded
Pisum chromosomes in 1981 (4).
In 1982 our institute again took up the problem of banding Pisum
chromosomes. The method used is a modification of those described by
Lamm (4), Marks and Schweizer (5), and Schweizer (pers. comm.). This
new attempt has yielded a heterochromatin pattern by which the single
chromosome can more or less be identified. Yet, this time too, many
difficulties had to be overcome. Typically fewer than 10% of the slide
preparations could be analyzed. This in part is due to an extremely Low
and varying mitotic index of Pisum root tips, and in part to the method
itself. Only in some few cells is the banding pattern sufficiently
clear. In general either the chromosomes are homogeneously stained, or
the pattern is incomplete, or the chromosomes are extremely swollen and
unstained. Often all these shortcomings are found on the same slide,
and we are unable to give a satisfactory explanation for them.
The distribution of heterochromatin in normal Pisum chromosomes is
shown in Figs. 1 and 2. Heterochromatin is found in the centromere
regions and on the telomeres, the amount being different in different
chromosomes. A rather large quantity of heterochromatin is situated
near the NOR region of chromosomes 4 and 7. Few intercalary bands of
heterochromatin are evident. However, banding clearly is visible on the
long arm of chromosome 7 proximal to the centromere region, and also on
the short arm of chromosomes 4 and 7 as well as near the centromere
region of chromosome 3 (long arm) and on the long arm of chromosome 5
(Fig. 2). This pattern is found in all metaphases which can be analyzed
reliably.
We have applied this C-banding technique to a reciprocal transloca-
tion genotype. We knew from earlier investigations of this genotype
that chromosomes 5 and 7 are involved in the exchange processes. Fig. 3
