Q. Briefly explain about semantides?
The information carrying molecules in plants are called semantides, and they have been recognised to be 3 kinds; deoxyribonucleic acid or DNA (primary semantide), ribonucleic acid or RNA (secondary semantide) and proteins (tertiary semantide) following the sequential transfer of the genetic code. Of these, the proteins are the most favoured molecules for chemotaxonomic purposes. Plant proteins can be studied by different methods; by electrophoresis or by serological methods, and both processes have been used for obtaining information about the protein chemistry of different plants.
In the common bread wheat, Triticum aestivum, the storage proteins were analysed by. electrophoresis. For comparative purposes, the storage proteins of the- tetraploid wheat, Triticum dicoccum and the dipliod grass Aegilops Squarrosa were also analysed electrophoretically study confirmed the conclusion that the hexaploid wheat did contain a sum of the proteins possessed by the diploid species which have contributed to the evolution of the hexaploid wheat. This study supports the observations based
on morphology and cytological evidence
Serological analysis of proteins is based on the immunological reaction shown by mammals when a foreign protein is introduced into the system. In other words, this is based on the antibody-antigen reaction, the antibodies being specific to an antigen bringing about coagulation. This information can then be analysed to understand the relationships of the different plants on the basis of the serological evaluation of the plant proteins. Serology has proved a useful taxonomic tool at different levels of classification. J. G. Hawkes (1960) and his co-workers studied several tuber-producing species of Solanum to understand the evolution of the cultivated potato Solanum tuberosum and determine the species of Solanum which could be established as the ancestors of the common cultivated potato, Similarly, in the family Ranunculaceae, serological studies supported cytological data for the classification of the family into tribes and genera. Fair brothers (1959) and his CO-workers have studied several plant groups serologically particularly the members of grass family. A general conclusion from such studies is that the different amount of serological activity in members of, different plant families may be interpreted as a reflection of the evolutionary differences in the primary structure of the proteins due to which serological differences can be recognised between members of different families.