BGN 12: The rupture of radiation inducing bridges in barley BARLEY GENETICS NEWSLETTER, VOL. 12, II. RESEARCH NOTES
Chandra and Makde, pp. 11-13

II. 3. The rupture of radiation inducing bridges in barley.

Avinash Chandra and K. H. Makde, Department of Botany, Dharampeth Mahavidyalaya, Nagpur 440 010 (M.S.) India.

Dry (8.1% moisture) and dormant seeds of spring two-rowed barley (Hordeum distichum L., 2n=14) var. Clipper were exposed with 5, 10, 15, 20, 30, 40 and 50 kR doses of 60Co gamma-rays at 2.2 kR/minute intensity, at the Division of Genetics, I.A.R.I., New Delhi. Irradiated seeds were sown in the field under usual agronomic practices. For meiosis, the plants were chosen on the basis of pollen sterility and phenotypic differences. Pollen viability was tested with the help of Alexander stain. Meiosis was studied in pollen mother cells using aceto-orecin, whereas root tips were squashed and stained with Leuco-Basic Fuschin.

The experimental findings are presented in Table 1 and Plate 1. It was observed that the frequency of bridges increases at higher doses. Behaviour of the chromosomes at anaphase was due to the occurrence of bridges of different types, with or rarely without chromatin fragments.

Table 1. Showing induced bridges in barley.

Figures 1-6.

Single (Fig. 1) and double bridges were frequent but triple bridge (Fig. 2) was only observed at 40 kR doses. In some cases the irregular formation of bridges by nonseparation of the chiasmata was due to stickiness (Fig. 3). Such stickiness might have been caused due to disturbance at cytochemical level by the secondary effects of radiation. Similarly splitting of bridge at one pole (Fig. 4) also occur and it is further bifurcated (Fig. 5) due to the effect of radiation at molecular level. Though this is of rare occurrence, it has its own importance in the D.N.A. synthesis or protein synthesis. In some cases, at telophase besides the chromatin bridges a small micronucleus was observed near one of the poles, which had chromatin attachment with the daughter nucleus of that pole (Fig. 6). The single and double bridges at anaphase I might have resulted either from dicentric chromatids or chromosomes respectively.

Acknowledgment:
The authors are thankful to Principal V. B. Phatak for providing facilities.

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