RESUMO
Female meiosis was analysed in squash preparations of ovules from three meiotic mutants and wild-type plants of tomato. In the completely asynaptic mutant as6, chromosome pairing and chiasma formation were virtually absent in both sexes. In the partially asynaptic mutant asb, with intermediate levels of chromosome pairing at pachytene, there were a higher number of chiasmate chromosome arms in female meiosis than in male meiosis, whereas in the desynaptic mutant as5 there were normal levels of chromosome pairing at pachytene and a similar reduction in chiasma frequency in the two sexes. In wild-type tomato, we found slightly higher numbers of chiasmate chromosome arms in female meiosis than in male meiosis. We propose that the higher female chiasma frequencies in mutant asb and wild-type tomato result from a longer duration of female meiotic prophase. This would allow chromosomes more time to pair and recombine. It is possible that a longer duration of prophase I does not affect mutants as5 and as6, either because the meiotic defect acts before the pairing process begins (in as6) or because it acts at a later stage and involves chiasma maintenance (in as5).
RESUMO
Synapsis and chiasma formation were studied in pollen mother cells of four meiotic mutants of tomato. The four mutants displayed defects in the assembly of the synaptonemal complex (SC) covering the whole range from almost complete absence of synapsis to complete synapsis at pachytene. In three mutants, we found a good correlation between the number of bivalents connected by at least one tripartite SC segment at pachytene and the number of chiasmatic bivalents at metaphase I. We suggest that in tomato functional chiasmata are only formed in the context of the tripartite SC.
