PNL Volume 15

1983

RESEARCH REPORTS 33

CYTOLOGICAL STUDIES OF L-108. NILSSON'S N II

Lamm, R. L. The Swedish University of Agricultural Sciences

Alnarp, Sweden

In his Botanical Review article of 1962, S. W. Yarnell presented

data and references concerning the then current status of translocation

lines in Pisum (4). The G-line of his survey corresponds to my L-108,

Nilsson's N II, T(2-6)a. I have completed the investigations published

earlier by a study of the karyotype of L-108 and by linkage determina-

tions between the T-point of this line and six marker genes of the

chromosomes involved.

W. Gottschalk states, after a study of 24 translocation lines in

Pisum, that in mitotic metaphase plates only relatively drastic inter-

changes can be reliably discerned (1). In L-108 at least one of the

interchanged cnromosomes is very easy to recognize by its small size and

by a submedian primary constriction. The shortest chromosomes of the

standard karyotype, viz. chromosomes 1 and 2, have about the same length

and yet cannot be confused with the still shorter 6² interchange

chromosome. For a reliable recognition of the 2⁶ chromosome, however,

measurements are desirable since it might otherwise be confused with

chromosome 6 of the standard type. The structure of the interchange

characterizing L-108 is explained by the drawings in Fig. 1. These

drawings are founded on measurements of eleven good mitotic metaphase

plates of L-108.

An account of the linkage studies performed with L-108 in crosses

with lines of the standard structural type is given in Tables 1 and 2.

The results of cross Nos. 2 and 7 have been published earlier (3). Data

concerning the backcross Nos. 3, 6 and 8 have been kindly put at my dis-

posal by Dr. E. Nilsson. In future investigations it would be desirable

to include at least three other genes, viz. .ar, mifo and i. Apart from

the incompleteness and somewhat vague results of the present linkage

studies, I have marked the approximative sites of the genes of Table 2

in the tentative diagram for the pairing at the prophase of meiosis in

Fig. 1. As regards the genes of chromosome 6, the suggested localiza-

tions are supported by the results of other investigations (2). At the

first metaphase of meiosis in the translocation heterozygote, chiasmata

never occur in the interstitial segments indicating that the T-point

must be proximal to the centromeres of the chromosomes forming a ring of

four (cf. Fig. 1).

Finally, it should be mentioned that trisomic plants have been ob-

served in the progenies of crosses between L-108 and lines of standard

structural type. A cytogenetical analysis, however, has not been

performed. The leaflets of these trisomies were broad and of the same

type as those described from crosses with L-114, Nilsson's N I, T(4 6)a

(2).

1. Gottschalk, W. 1978. The Nucleus 21:29-3*».

2. Lamm, R. 1982. PNL 14:32-35.

3. Lamm, R. and R. J. Miravalle. 1959. Hereditas 45:417-440.

4. Yarnell, S. H. 1962. The Bot. Review 28:465-537.



PNL Volume 15 1983	RESEARCH REPORTS	35

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Fig. 1. Interpretative drawings of the reciprocal translocation charac- teristic of L-108 and illustrations of mitosis in root tips of L-110 (the standard structural type) and L-108, T(2-6)a. Below, a tentative diagram for the chromosome pairing at the prophase of meiosis in the F1 hybrid between these lines with a very approximative location of six marker genes together with illustrations of the ring of four at the first metaphase of meiosis. Bars represent 10 mkm