Desynaptic Mutant Research Articles

Radiation Induced Desynaptic Mutants in Barley

Radiation Induced Desynaptic Mutants in Barley

Analysis of Desynaptic Mutants Induced inDurumWheat (Triticum DurumDesf.)

SUMMARYFive desynaptic mutants isolated in M2 confirmed in M3 and cytologically analyzed in M4 have been investigated. Two of these (DS1 and DS2) were isolated in the cv. Cappelli after seed treatment with Ethylmethansulphonate (EMS), and thermal neutrons respectively. The other three (DS3, DS4 and DS5) were isolated in the cv. Aziziah after seed treatment with thermal neutrons, EMS and fast neutrons, respectively.For genetic analysis of mutation the segregation ratio for each mutation was calculated in individuals of five generations (from M3 to M2).To ascertain whether the cytological behaviour could have been influenced by the environmental conditions, a DS1 mutant was grown both in field and controlled conditions (20°C, 12.000 lux for 18 hrs. per day) in a growth chamber.In all five mutants the behaviour during microsporogenesis was almost the same. In fact, no significant difference in the mean number of chiasmata per cell was found either between the two control lines (Cappelli and Aziziah), or betw...

Induction of chromosome aberrations by X-rays and chemical mutagens in a desynaptic mutant and in wild-type barley

It has previously been proposed that eukaryotes with a genetically determined abnormality in the sequence of events leading to normal chromosome exchange at meiosis, might be expected to show an altered response on the part of their somatic cell chromosomes following exposure to chemical or physical mutagens. As part of a programme undertaken to examine this contention, dry and soaked seeds of a wildtype ( Ds Ds) and a desynaptic mutant ( ds ds) of barley were exposed to X-rays and the frequency of chromosome-type aberrations determined in cells in their first post-irradiation mitosis. Preliminary experiments with these materials by Riley and Miller had pointed to an increase in yield of aberrations in cells of the mutant relative to the normal, but no such difference could be demonstrated in the present more extensive experiments. Seeds and root-tips were also exposed to the chemical mutagens nitrogen mustard and diepoxybutane and a detailed analysis of the induced chromatid-type aberrations revealed no difference in the sensitivity of ds ds and Ds Ds genotypes. The frequency of sister chromatid exchange were studied in autoradiographs of root-tip cells in their second mitosis following exposure to [ 3H]thymidine. There was no difference in the incidence of such exchanges between cells from the different genotypes.

Effect of temperature and barbiturates on a desynaptic mutant of ryegrass.

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.