In 1982 (MNL 56:2-4) we described a possible synergistic effect between Mu and ultraviolet light (UV) in pollen. In 1982 we planted the remaining seeds of the crosses described in the 1982 report. This provided larger populations from which a more accurate estimate of the synergistic response could be obtained. The results are given in Figure 1. The new curve substantiates the synergistic effect reported in the 1982 report. It now appears that the synergistic response increases in a linear fashion to a peak at 35 seconds and then decreases linearly to 45". This pattern suggests that Mu and uv interact to give a greater than additive effect. Since it is not known whether or not Mu alone acts in the pollen to induce mutants, there are two possible explanations for the synergistic effect. 1) If Mu is active in pollen, synergesis could be due to the enhancement of Mu activity when it is irradiated. 2) If Mu has no mutagenic activity in the pollen, it could be activated when pollen is irradiated. No matter what the explanation this synergistic response falls off at higher doses than 35 seconds. Why? Is it possible that at doses higher than 35 seconds uv inactivates Mu? If the trend continues, there should be no synergistic effect observed at 50 seconds or higher doses. Tests of the effect of doses above 45 seconds were made this year, but the results are yet to be analyzed. If high doses of uv do inactivate Mu and the inactivation is permanent, all plants resulting from irradiated Mu pollen at doses of 50 seconds or higher (if synergesis is indeed not observed at higher doses) should have lost Mutator activity.
Donald S. Robertson
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