Maize mutant Adh1 as a tool to establish cause of Cg2 instability
--S. M. Buyukly and V. N. Lysikov
The Cg2 macromutation induced in stock VIR-44 by g-irradiation is unstable. At early ontogenesis stages Cg2 mutates both from Cg2 to + and in the reverse direction to Cg2 (Lysikov, VN, Krivov, NV, and Golubovsky, MD, Genetica 20:89-99, 1984). In order to test the hypothesis that Cg2 instability is connected with transposition of previously unknown mobile elements an approach consisting of using the pollen selection system of alcohol dehydrogenase negative mutants and their characteristics at a molecular level was proposed.
Adh1 null mutant search was carried out by means of pollen sensitive to allyl alcohol treatment (Schwartz, D and Osterman, D, Genetics 83:63-65, 1976). About 500 plants of several derivatives carrying the Cg2 gene were self-pollinated with pollen treated with allyl alcohol. When pollen is treated, ADH in pollen grains reacts with allyl alcohol and converts to the highly toxic acrolein. Wildtype pollen grains which contain active enzyme perish, while mutant ones which lack ADH activity survive and take part in fertilization. Ears pollinated with treated pollen had kernels from three to five in an ear and totalled 944. All the kernels were sown in a field, but only 400 plants came to the reproductive stage. Some seedlings did not germinate, some seedlings died at the 3-5 leaf stage. Screening of ADH+/ADH- heterozygotes was carried out in F1 by means of specific pollen staining for ADH (Freeling, M, Genetics 83:701-717). Wildtype pollen grains stain shiny opaque blue, but ADH- grains are yellow-pink, translucent. Only 3 plants had both ADH+ and ADH- pollen grains out of a total number of 389 plants tested with pollen staining for ADH. However, the ADH+:ADH- ratios (10:1, 2:1, 2:1) differed from the expected one (1:1). An F1 generation (120 seeds) was obtained only from one of the 3 heterozygotes. This mutant was designated Adh1-27.
New mutations phenotypically like yellow stripe-1 and red aleurone were discovered after self-pollination in one of the families in F2 and F3 generations of the Adh1-27 mutant and besides they appeared simultaneously in the same plant. Earlier in F1 a mutation was found that was phenotypically similar to striate. Thus, in spite of the fact that molecular genetical investigation did not prove the above mentioned hypothesis, we assume that there are relationships between Cg2 instability and transpositions of mobile genetical elements; supposed insertion mutant Adh1-27 segregated and new mutations were found in generations.
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