| Chemical inducion of mutation in common wheat J. MAC KAY Swedish Seed Association, Svaloef, Sweden In the search for more efficient mutagens and means to direct the mutation process, the Swedish mutation research has turned more and more over to the study of chemical mutagenesis. Seeds, mainly of barley and peas, have consistently been used in these experiments, and up to now a series of alkylating compounds (mustard gas, nitrogen mustards, diethyl sulfate, ethylene oxide, glycidol, ethyleneimine, epichlorohydrine, methyl, ethyl and propyl methanesulfonate, diepoxybutane, triethylenemelamine, myleran), oxidizing or substituting agents (oxygen, p-dioxan, chlorine, iodine), and purine derivatives (8- ethoxycaffeine, nebularine) have been investigated as to their effect on survival, fertility, mutation frequency and spectrum. The results have been very encouraging. Thus, treatments with ethyleneimine and alkanesulfonic esters gave the same or even higher mutaion rates in M2 than X-irradiation. In addition, the mutation spectrum was changed, and entirely new mutant types could be found (cf. EHRENBERG et al., 1961. Hereditas 47 : 243-281). In general, chemical mutagenesis also proved less associated with sterility in the first M-generation, which must be taken as an indication of a relative prevalence of point over chromosome mutations. This interpretation has also been supported otherwise, e.g. by cytological analyses of primary effects. This shift in mutation mechanism inherent of many chemicals studied can, however, be expected to alter the evaluation in connection with polyploids. The visible mutation spectrum is here generally representing more drastic events than a gene or point mutation which easily will be phenotypically suppressed by the reduplicated genic system typical for this category of plants. In order to study this aspect, a series of experiments in 6x vulgare wheat was performed in 1957-60. Besides X-rays and fast neutrons, five different alkylating agents were tried. Ethylene oxide, ethyleneimine and ethyl methanesulfonate are easily soluble in water and were used in a series of successively increasing concentrations. Originally dry seeds were soaked in the solutions at room temperature and due to the different penetrating ability of the three substances for 5, 6, and 24 hours, respectively. Diethyl sulfate and especially myleran are less soluble in water, and therefore time of treatment in a saturated solution was here used as varying factor. Since ethyleneimine, ethyl methanesulfonate and diethyl sulfate are unstable at low pH values, a Tris buffer was added to keep pH at 7.6-7.7. and, in addition, the continuous shaking occurred in open flasks to accomplish a certain aeration. |
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