Meiotic mutants of Medicago sativa show altered levels of alpha- and beta-tubulin

We have analysed the level of accumulation of alpha- and beta-tubulin polyp eptides in flowers collected from different meiotic mutants of alfalfa (Med icago sativa L.). The H33 mutant previously identified as a producer of mal e and female gametes with the somatic chromosome number (2n gametes) as a r esult of defective spindle orientation or, more rarely, abnormal cytokinesi s, showed a higher level of alpha- and beta-tubulin compared to control dip loid plants and approximately the same level as control tetraploid plants. A higher level of tubulin was likewise observed in diploid plants displayin g abnormalities in spindle orientation and cytokinesis, which had gone thro ugh 3-4 cycles of phenotypic recurrent selection to increase 2n gamete prod uction. A similar analysis was performed on another class of Medicago meiot ic mutants characterized by production of 4n pollen (jumbo pollen, due to t he absence of cytokinesis at the end of meiosis) and 2n eggs. Again, the le vel of alpha- and beta-tubulin was found to be higher in the mutants than i n diploid controls. We conclude that meiotic defects, such as abnormal spin dle orientation or cytokinesis leading to the formation of 2n gametes, dete rmine an increased level of tubulin, the main constituent of plant microtub ules (MTs).