Effects of x-rays on frequency of mutations in hydrated wild-type tomato pollen

Abstract

Wild-type tomato pollen was treated at 2 temperatures, subjected to 5 moisture treatments and 5 X-ray exposures. In addition, pollen treated as above was stored dry for 1 day before pollination. The major problem was to evaluate the effects of X-rays on the frequency of mutations in hydrated pollen. Here, response was measured using these 5 criteria: (1) seed set, (2) R 1 seed germination, (3) R 1 phenotypic changes, (4) R 1 pollen fertility and (5) R 2 mutations from R 1 plants. The data on seed set supported the hypothesis that: ( a) Seed set was decreased with an increase in dose when pollen was treated at 25 °C. However, seed set was generally higher when pollen was treated at 0 °C. ( b) Treated dry pollen set less seed than moist pollen. There were only slight differences in seed set due to moisture per se but hydrated pollen treated at 25°C for½ hr and at 0 °C for 3 hr gave the best seed set. In general, the LD 50 based on average seed set for dry and hydrated pollen was not the same for 25 and 0 °C. ( c) Pollen stored in hydrated condition produced less seed than non-stored hydrated pollen. Dry pollen treatments were shown to reduce seed germination of the R 1 In general, the percent seed germination of the R 1 derived from treated dry pollen was lower than that from irradiated hydrated pollen. Pollen treated at 0 °C yielded R 1 seed that germinated better than R 1 seed derived from pollen treated at 25 °C. Among the recovered R 1 seedlings with phenotypic changes, morphological off-types occurred more frequently than chlorophyll and B types. A high percentage of these types, however, were not recovered in the R 2 generation. At 25 °C, treated dry pollen and treated moist pollen yielded the same total percentage of R 1 seedling off-types. On the other hand, differences in R 1 types were shown at 0 °C. That is, pollen treated dry yielded more off-types in the R 1 than pollen humidified for ½ hr at 0 °C. The phenotypically normal R 1 plants were classified for pollen fertility. The data from both 25 and 0 °C treatments indicated that pollen fertility of the R 1 plants decreased as a result of dry pollen irradiation. In addition, pollen fertility was shown to decrease with an increase in X-ray exposure at both 25 and 0 °C. Finally, the percentage of R 2 families that segregated for mutations was relatively high after dry pollen treatments at 25 °C. At 0 °C, there were little differences between dry and moist pollen treatments.