New meiotic mutations isolated from Mu and Ac stocks
--W. F. Sheridan, I. N. Golubovskaya and Don Auger
The goal of this experimental work was the isolation of new tagged mutations of maize meiotic genes. For this purpose 584 families of 20 kernels each were planted from self-pollinated ears produced with active Mutator stocks. In addition 150 families of 20 kernels each were planted from self-pollinated ears of Ac stocks. The Ac material was produced in the previous generation by planting kernels that were selected on the basis of containing a transposed Ac element. These materials were planted in the field in Grand Forks in 1992 and checked for segregation for male sterility.
We have isolated 75 families from the Mu background belonging to 15 independent sources and 15 other unique families from the Ac background that segregated male sterile plants. Twenty kernels from each of these families were planted in the Hawaii winter nurseries. The young tassels of 6-15 plants were sampled in 56 families derived from the Mu background which belonged to 10 independent sources and in 8 families from the Ac background. Tassels were fixed in Farmer's fixative (3:1), and all sampled plants were grown to flowering. During pollen shedding the phenotype (fertile/sterile) of each plant was checked in the field, and microsporocytes from fixed tassels of each sterile plant were examined under the light microscope.
Five new meiotic mutations were identified: four induced by Mu and one by Ac. One of the Mu background families segregated sterile plants with an ameiotic pattern of meiosis, eight families (selfed sibs) segregated sterile plants with a severe desynaptic phenotype. Three families (selfed sibs) segregated sterile plants with meiocytes stopped in different stages of meiosis from prophase I onward. In spite of the complete formation of the pollen envelope, we could easily identify at what stage was meiosis stopped. Finally, two families (selfed sibs) segregated sterile plants with abnormal segregation of sister chromatids at the second meiotic division. Meiosis of sterile plants was normal before metaphase II and anaphase II and exhibited no visible abnormalities prior to these stages. The meiotic phenotype of these sterile plants was similar to that described in Drosophila melanogaster mutation S 332a (Davis, MGG 113:251, 1971; Goldstein, Chromosoma 78:79, 1980).
The one family from the Ac background segregated sterile plants with abnormally condensed chromosomes at metaphase I. This phenotype was the same as that described for the dominant meiotic mutation designated as Mei 025 (Golubovskaya, Adv. Genet. 26:149, 1989).
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