| Evidence of heterochromatin polymorphism through crossing-over1)
R.J. SINGH Insittut fur Pflanzenbau und Pflanzenzuchtung der Universitat, von-Siebold-Strasse 8, D-3400 Gottingen, Fed. Rep. Germany Polymorphism in heterochromatic chromosome segments has been reported in Anemone (MARKS and SCHWEIZER 1974), Tulipa (FILION 1974), and rye (WEIMARCK 1975). SINGH and ROBBELEN (1975) also found a wide variation in pattern of heterochromatic bands, both between and within species of Secale. Since the SAT-chromosome was most easily recognized, four structural types of it could be distinguished by their different Giemsa banding pattern in twenty seeds of Secale africanum; one of these types was always more frequent than the others. In order to obtain more information on the mechanism, by which changes in banding pattern of chromosomes occur, one plant of Secale africanum with known banding pattern was allowed to self-pollinate. Spikes were bagged to avoid contamination with foreign pollen, although S. africanum is an autogamous species. From the resulting seeds several types of Giemsa banding of SAT-chromosomes were determined in root tips (Fig. 1). All plants with a particular banding pattern were grown in the greenhouse; root tips were recollected 26 days after the first analysis of primary roots was made, in order to check whether bands were changing during somatic cell division. If meiotic crossing-over is assumed not to occur within the distal heterochromatic regions (NATARAJAN and GROPP 1971), but only in the median euchromatic parts of the SAT-chromosomes, a total of 10 banding types is expected from a heterozygous plant (Fig. 1). With designation of the parental banding types as A and B and the crossing-over types as C and D, there will be 4 homozygous (AA, BB. CC, DD) and 6 heterozygous (AB, AC, AD, BC, BD, CD) combinations of SAT-chromosomes. Twenty six seeds were studied with Gimesa, and all of the expected heterozygous and two homozygous (BB, DD) types were observed in various frequencies. AA and CC types were not detected within the limited number of analyzed individuals (Fig. 1). The maximum frequency in heterozygous types was for BD (9), and the lowest for BC (1). The occurrence of one type in higher frequency than others indicates preferential transmission through the gametes. No somatic instability was ascertained. Thus, the study provides direct cytological evidence that meiotic crossing-over causes polymorphism in hetero- chromatin of rye chromosomes. Literature Cited FILION, W.G. 1974. Differential Giemsa staining in plants. I. Banding patterns in three cultivars of Tulipa. Chromosoma 49: 51-60 MARKS, G.E. and D. SCHWEIZER 1974. Giemsa banding: Karyotype differences in some species of Anemone and in Heptica nobilis. Chromosoma 44: 405-416 NATARAJAN, A.T. and A. GROPP 1971. The meiotic behavious of autosomal heterochromatic segments in Hedgehogs. Chromosoma 35: 143-152 SINGH, R.J. and G. ROBBELEN 1975. Comparison of somatic Giemsa banding pattern in several species of rye. Z. Pflanzenzuchtg. 75: 270-285. WEIMARCK, A. 1975. Heterochromatin polymorphism in the rye karyotype as detected by the Giemsa C-banding technique. Hereditas 79: 293-300 (Received November 20, 1976) |
| 1) Supported by Deutsche Forschungsgemeinschaft. |