Maize
Genetics Cooperation Newsletter 80. 2006.
Saratov State University
We reported earlier about the production of maize lines predisposed to reduced parthenogenesis and autonomous endospermogenesis (MNL 71, 1997; MNL 75, 2001; and other articles in Russian). The frequency of parthenogenesis can reach 100%. The sign is nuclear and can be transferred to other lines by egg or pollen. On the basis of these lines, we carried out work on the production of apomictic maize forms. According to the literature, higher levels of ploidy than 2n (from 3n and higher) are characteristic for many apomictic species. Therefore, we have made experiments on the production of tetraploid analogies for previously obtained diploid parthenogenetic lines (AT-1 and AT-3). We have demonstrated before that after treating parthenogenetic diploids with colchicine, a great number of maternal-type diploid plants appear (MNL 77, 2003). The same results were obtained in the experiments in the next year. This indicates indirectly that the ability for parthenogenesis was not lost by the formation of diploid eggs.
In addition, we carried out research on the production of tetraploids forming spontaneously through the use of unreduced pollen. This approach is interesting, as it does not exclude the probability of production of lines with genes for non-reduction, which can be useful in the subsequent work of producing unreduced apomicts. As the maternal form, we used the ordinary tetraploid with yellow kernels. It was pollinated by pollen of line AT-1, characterized by purple color of plants and kernels. Such crosses were used for control in the event of occasional pollination by pollen from maternal tetraploids. Along with triploids, a small number of tetraploids were produced, which were self-pollinated. In self-pollinated progeny in three plants, 219, 189 and 124 embryo sacs were isolated by the ovule enzymatic maceration method, and were analyzed. In two embryo sacs of one plant we observed autonomous embryogenesis. In one of these embryo sacs the cellular embryo was found. In the second embryo sac, we observed simultaneous development of two embryos (6- and 8-cellular). In another plant one case of autonomous endospermogenesis (0.8%) was observed. Cases of atypical organization of embryo sacs that are characteristic for the initial diploid parthenogenetic line were also observed: synergid-like eggs with the nucleus in the basal position (2.1% and 4.1% in two plants), additional (7 and 8) cells in the egg apparatus, and additional (3, 4 and 5) polar nuclei. In all three plants there were very large 1-4 nuclear cells adjoining the antipodal apparatus (1.% - 4.0%).
Thus, the direct cytoembryological analysis has shown that in tetraploid analogies the ability for parthenogenesis, autonomous endospermogenesis and other characteristics of the embryo sac can manifest in the same way as in the initial diploid lines.
The possibility of the connection of additional cells with apospory and the reasons (heterozygosis, age of eggs and others) for relatively low frequencies of parthenogenesis and endospermogenesis are not clear for the present, and require additional research.
_________________________________________________
Please
note:
Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only
with consent of the authors.
Return to MNL 80 on-line index.
Return to MNL index.
Return to MaizeGDB home page
____________________________________________