| Molecular approach to the phylogeny of wheat C. R. BHATIA1) Biology Department, Brookhaven National Laboratory, Upton, N. Y., U. S. A. Bread wheat plant contains a large number of enzymes, which directly or indirectly are responsible for all morphological and physiological characteristics. The enzymes that we have studied so far, esterases, peroxidases, alcohol dehydrogeanse and leucine amino peptidase occur in multiple molecular forms. It is very likely that most, if not all other enzymes also occur in different molecular forms. Functionally similar, though not structurally identical enzymes are present in diploid and tetraploid species of wheat. Each of these enzymes is made of one or more polypeptide chains, and on the basis of our present knowledge of protein synthesis, we can say that the primary structure of each polypeptide chain is determined by the nucleotide sequence of the DNA in the structural gene. For any specific enzyme, this information should be highly redundant in hexaploid species, being contributed from three parental genomes. Molecular heterogeneity of enzymes can be studied in a number of different ways, among others by characterizing their electrophoretic mobility, serological behaviour, reaction with coenzyme analogues and of course, by determination of the amino acid sequence. Some of these tests can be performed on relatively crude extracts. We have studied electrophoretic mobilities of few enzymatic proteins using polyacrylamide gel electrophoresis. By this technique it is possible to separate proteins from complex mixtures, on the basis of net charge and size of the molecule. The results indicate that bread wheat varieties of very diverse origin show a fairly uniform pattern with respect to the specific enzymes studied, though a few genetic variants were also observed. The enzyme heterogeniety is much greater between the species and between species of different ploidy. The present molecular forms in the hexaploid species must have evolved from the original forms contributed by the parental species. By further chemical characterization of the molecular homologies of a specific enzyme in hexaploid, tetraploid and diploid species, probable genome donors, their hybrids and the synthesised polyploids it should be possible to infer evolutionary relationships and to trace back the evolutionary pattern of the genetic loci controlling these enzymes. Further, on the basis of this information, some of the molecular alterations in the DNA contributed by each of the genome donors can be infered. This considered in conjunction with the available morphological and cytogenetical evidence will help in elucidating evolutionary relationships. (Received Jan. 10, 1967) |
| 1) Prcsent address: Biology Division, Atomic Energy Establishment, Trombay,
Bombay, India. Research was carried out under the auspices of the United States Atomic Energy Commission. |