Institute of Plant Industry
Macrosporogenesis in both normal plants and mei-mutants
--N. A. Avalkina and I. N. Golubovskaya
Recently an enzyme squash technique on isolation of archeosporic cells undergoing meiosis (Jongedijk, Stain Technol. 62:135-142, 1987) has been adapted to maize. It permits the study in detail of both female meiosis and embryo-sac development. In normal plants the main distinction between the male and female meiosis is revealed at second division. As a rule in macrosporogenesis the 2nd meiotic division proceeds nonsimultaneously in dyad cells, and in micropylar cells the second division is delayed or completely stopped at metaphase 2 - telophase 2 (Figure 1).
The squash technique is convenient for solving cytogenetic problems, for example, an effect of mei-genes, impairing different key cytogenetic events of meiosis, both in micro- and macrosporogenesis. The character of meiosis in an ameiotic maize mei-mutant is shown in this paper. The ameiotic recessive allele in the homozygous state is responsible for meiosis substitution by mitosis. In microsporogenesis in meiocytes of ameiotic homozygotes, synchronous mitosis proceeds instead of meiosis (Palmer, Chromosoma 35:233-246, 1971).
The female meiosis in ameiotic homozygous mutants has been studied, and the pattern of irregularities in female meiosis is similar to ones in male meiosis. Different stages of ameiotic mitosis (interphase, prophase . . . telophase) are observed (Figure 2,a-h). The ameiotic mitosis in macrosporogenesis is completed by formation of dyad cells, but a great number of them are degraded (Figure 2i). Rare triads or tetrads occur.
For the first time we have the opportunity to visualize the real effect of mei-genes in female meiosis. The enzyme squash technique used here is convenient for solving some questions of the great problem of genic control of meiosis.
Figure 1. Female meiosis in normal fertile plants. a) interphase, b) pachytene, c) diakinesis, d) metaphase I, e) dyad cell, f) tetrad
2. Female meiosis in ameiotic mei-mutants. a) interphase, b)
prophase, c-d) metaphase, e) anaphase, f-g) telophase, h) dyad cell, i)
degenerated dyad cell.
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