Reference
Genetics Lab., Biology Dept., Wuhan University, Wuchang, Hubei, China
For karyotype analysis of somatic chromosomes, root-tip cells are often used.
Although a number of seeds are necessary for this, the number of seeds
available is often limited, such as in species hybrids. We have attempted to
use subcultured somatic calli for karyotype analysis.
Dehulled seeds of a Keng (Japonica) variety, Jing Hong 2, were sterilized in 0.1% HgCl\2\ for 20 minutes, steeped in 70% ethanol for 1 minute. They were then rinsed with sterile water several times and were then put onto MS medium containing 3% sucrose. Five days later, the endosperm and radicle were removed from the germinating seedlings and the remaining part was placed on an N6 medium supplemented with 2 mg/l 2,4-D and 4.5% sucrose.
Milk-white calli were formed at the base of the young plants. For preparing chromosome samples, the cell wall digestion-hypotonic expansion-flame drying method (Kurata and Omura 1978) was employed. The karyotype of Jing Hong 2 was found to be: 16m+2 st (Fig. 1). Small clumps of tender milk-white calli close to the medium were suitable for karyotype analysis. There was no distinct peak time in cell division. By subculturing, we could ensure a continual supply of abundant calli.
Fig. 1. Somatic chromosomes observed in a callus cell.
Reference
Kurata, H. and T. Omura, 1978. Karyotype analysis in rice, 1. A new method for identifying all chromosome pairs. Jpn. J. Genet. 53(4):251-255.