Abstract
Abstract In microsporocytes of a diploid desynaptic mutant ds ds of ryegrass, high temperature markedly increased the degree of desynapsis while barbiturates decreased it. The mean bivalent number per cell was 5.39 ± 0.068 at 28° and 6.71 ± 0.040 at 11°. Similary, the mean chiasma number per bivalent was 1.37 ± 0.017 at 28° and 1.75 ± 0.30 at 11°. The differences were highly significant. Treatment with 5-ethyl,5-phenylbarbituric acid and 5,5-diethylbarbituric acid at 26° significantly increased the mean bivalent number per cell to 6.78 ± 0.034 and 6.60 ± 0.067, respectively, compared to 4.98 ± 0.388 in the controls treated with distilled water. Since temperature variations disrupt hydrogen bonds in DNA and barbiturates form strong bonds with adenine derivatives, it is hypothesized that hydrogen bonding in some form in involved in keeping the chromosomes paired asfter their initial synapsis. The desynaptic mutant is perhaps defective in a thermosensitive compound controlling hydrogen bonds in the condensation of chromosomes.
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