Comparative study of two annual Medicago species: Cytogenetical approaches and seed storage proteins analysis in M. polymorpha L. and M. laciniata (L.) Mill.

Species of the Medicago genus are of great interest for their ability to fix atmospheric nitrogen. Only a few species, mainly those used in agriculture, have been well studied. There is a particular lack of study of the annual wild species, which are represented in very small numbers (4/103) in the genus. This is why we have chosen to study two annual species with two different basic chromosome numbers, Medicago laciniata (L.) Mill. x = 8 and Medicago polymorpha L. x = 7. The main questions were to understand how the decrease in basic chromosome number from x=8 to x=7 occurred and what is the relationship between these species. To answer these questions, the karyotype was analysed using conventional karyological methods and the genome size was assessed using flow cytometry. Ten accessions of M. polymorpha and six of M. Laciniata were studied for cytogenetical feature (by classical karyological methods). Apart from the basic chromosome number, some differences in karyotype features such as chromosome size and morphology were observed. The mean genome size values were 2C = 1.817 pg for M. Laciniata and2C=1.123 pg for M. polymorpha. The SDS-PAGE gel analysis of the seed storage proteins showed species-specific polypeptides pattern. In addition to differences in the basic chromosomes number, karyotype characteristics and total nuclear DNA content, protein profiles also differ between the two species. We suggest that decrease in basic chromosome number from x=8 to x=7 is probably due to occurrence of Robertsonian fusion or centric fusion.