45 Identification of primary trisomics of rice through isoenzyme variation

Genetics Division, Indian Agricultural Research Institue, New Delhi, 110012 India

Keeping in view the limitations of cytomorphological parameters to distinguish trisomics that closely resemble among themselves as well as diploids, possibility of using electrophoretic variations of isoenzymes as supplementary criteria was explored in nine primary trisomics each of indica and japonica varieties (kindly provided by Dr. G.S. Khush, IRRI and Dr. J.N. Ruger, University of California, Davis, respectively). This was done on the assumption that genic imbalance of unspecified nature brought about by the third allele could impair or activate the catalytic function of an enzyme resulting in either increased activity or total supression of the concerned protein or appearance of a new fraction (McDaniel and Ramage 1970; Smith and Cocklin 1975). Zymograms of two non-specific enzymes viz esterase and peroxidase were analyzed through acrylamide gel electrophoresis using fresh flag leaf samples. The study revealed distinct differences in the zymogram patterns of both the varietal groups. In the case of esterases, there were respectively 6 and 9 types of zymograms in indica and japonica. In most of the cases there was line-specific zymogram pattern. 3.e and 5.3 types in indica and 4.e type in japonica were however, exceptions to the one line-one pattern relationship, as they included more than one trisomic line. In cases wherein more trisomics fell under a single zymogram type, they could be distiguished from each other on the basis of differential intensity of bands. For instance, triplo 7 (indica) and triplo 5 (indica) although had same number of bands as disomic line, they could be distinguised from each other on the basis of intensity difference of certain bands. In japonica, the variation was much more pronounced. The trend was by and large the same in respect of peroxidase zymogram pattern as well. In japonica series, expecially disappearance of bands in the Rf range of 0.51 and 0.79 and the new bands in the range of 0.26 and 0.33 characterized majority of the trisomics.

Quantification of the differences through the index of biochemical distance which was computed by taking into account the numerical and intensity variations of the bands between any two zymograms, confirmed further the uniqueness of each zymogram. For instance, such quantification revealed triplo 5 (indica) and triplo 7 (indica) which shared 3.e type with diploid to show more distance. Triplo 6 (indica) and triplo 10 (indica) which had 5.e type of zymogram could not, however, be clearly distinguisehd through this parameter, thus showing its limitation as well. In japonica series all trisomics showed good distance with diploid as well as among themselves.

Table 1 Zymogram patterns of esterase and peroxidase isoenzymes in primary trisomics of indica and japonica varietal groups.

McDaniel, R.S. and Ramage, R.I. 1970. Genetics of primary trisomics series in barley: Identification by protein electrophoresis. Canad. J. Genet. Cytol. 12: 490-495.

Smith, H.H. and Conklin, M.E. 1975. Effects of gene dosage on peroxidase isozymes in Datura stramonium trisomics. In Isozymes III. Academic Press, pp. 603-618