A case of genome partition in polyploid oats

At the second generation of the interspecific cross between the cultivated hexaploid (2n = 42) oat A. Sativa and the wild tetraploid (2n = 28) A. Murphyi, a plant having hexaploid and diploid (2n = 14) sectors was selected. Meiosis was highly regular in the diploid sector but the tillers failed to proceed beyond the boot stage and no seeds were produced. It is suggested that this diploid sector represents an entire genome of one of the diploid progenitors of the hexaploid oat.

Nuclear and cytoplasmic genome relationships in the genus Avena: analysis by isoelectric focusing of ribulose biphosphate carboxylase subunits

Comparisons of the isoelectric points of small and large subunits of ribulose biphosphate carboxylase extracted from a number of diploid, tetraploid, and hexaploid Avena species have been used to obtain information on the nuclear and cytoplasmic genome relationships within the genus. All species tested had small subunits with similar isoelectric points, so their analysis provided no information of taxonomic value. Three types of large subunits could be distinguished by this method, and the distribution of each among the available species provides strong evidence against the involvement of a C genome diploid (such as A. ventricosa) as the maternal parent in the formation of either tetraploid or hexaploid species. One type of large subunit was confined to the perennial tetraploid, A. macrostachya, and its position in the genus and possible origin are discussed. The value of this approach in studying genome relationships within the genus Avena and related genera is assessed.

EVOLUTION IN THE GENUS AVENA: INHERITANCE OF DIFFERENT FORMS OF RIBULOSE DIPHOSPHATE CARBOXYLASE

Disc electrophoresis of ribulose diphosphate carboxylases from Avena species in polyacrylamide gels of varying concentrations reveals the presence of two distinct forms of the enzyme. One migrates faster than the other and is found exclusively in species possessing the A genome. The other is confined to the C genome species (A. pilosa, A. ventricosa, A. clauda). The association of another characteristic of this enzyme (presence of stromacentres in the chloroplasts) with the A genome was reported previously. Observations on the recently described species A. prostrata, A. canariensis, A. damascena, and A. murphyi show that they all possess stromacentres, confirming reports that they all contain the A genome. Examination of amphiploid hybrids (from crosses between various diploid species and A. sativa) has shown that the mobility character is inherited maternally, and is located on the chloroplast genome. All these hybrids have the A genome and all have stromacentres. The results are discussed in the light of recent findings on the structure and synthesis of this enzyme. Consideration of the species distribution of the different forms of carboxylase places certain restrictions on the possible evolutionary paths from diploids to tetraploids and hexaploids.