Backcross populations (BC) from Medicago sativa L. x M. dzhawakhetica Bordz. hybrids were analyzed for chromosome number, fertility and morphological characteristics. Previously obtained F1 hybrids were recovered when diploid (2n = 2x = 16) M. sativa was crossed with tetraploid (2n = 4x = 32) M. dzhawakhetica. Resulting F1 hybrids were triploid (2n = 3x = 24), completely male sterile and had low levels of female fertility. Subsequent populations were obtained by successive backcrossing to unrelated (4x) M. sativa clones. The BC1 plants were pentaploid (2n = 5x = 40) and both male and female fertile. BC2 populations had chromosome numbers ranging from 2n = 32 to 48, and most plants (94% were male and female fertile. BC3 populations were tetraploid (2n = 32) or near tetraploid (2n = 33) and were morphologically similar to M. sativa. Preliminary analysis of mitochondrial nucleic acids by agarose gel electrophoresis, indicated biparental inheritance of this organelle in the F1 hybrids; however, further analysis provided inconclusive results.

To identify a model legume experimental system for studying low temperature signaling and cold acclimation, cold-induced expression and regulation of homologues of alfalfa (Medicago sativa) cold acclimation-specific genes cas15 and cas30 were examined in M. arborea (relatively frost tolerant) and M. truncatula (relatively frost sensitive). Both cas15 and cas30 genes are present in the genomes of both species but whereas both genes are cold-induced in M. arborea, only cas15 is induced in M. truncatula. Cold-induced expression of these genes is inhibited by calcium chelators and channel blockers and by the membrane fluidizer benzyl alcohol. Treatment of leaves with dimethylsulfoxide, a membrane rigidifier, induced both genes at 25°C. A cold-activated MAP kinase activity was expressed in both species. These results suggest that M. truncatula, an annual, self-pollinated species may be successfully used as model experimental systems in studies of cold signaling and role of cas genes in cold acclimation in legumes.

No description available.