A Database for Triticeae and Avena
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.
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
The authors are thankful to Principal V. B. Phatak for providing facilities.
BGN 12 toc
BGN Main Index