Fertilization with irradiated pollen in Tradescantia

Abstract

Flowers of diploid and tetraploid material of Tradescantia paludosa were pollinated with irradiated pollen. X-ray exposures of 1, 5, 10, 50 and 150 kR as well as gamma ray exposures of 500 kR from Co 60 were used. The flowers were fixed in Carnoy 1–56 hr and 3–15 days after pollination. At all the exposures studied the pollen was capable of germinating on the stigmas and the tubes were able to grow down to and penetrate the embryo sacs. In the pollen tube mitoses the following abnormalities were seen: chromosome stickiness, bridges and fragments. After exposures of 1–5 kR two sperm nuclei of equal or unequal size were formed, and these were not accompanied by fragments or connected by bridges. After exposures of 10–50 kR the sperm chromatin was highly variable and the following types were seen: undivided generative nuclei, two sperm nuclei of equal or unequal size with or without extra nuclear fragments and free or connected by bridges. After exposures of 150–500 kR undivided generative nuclei with or without nuclear fragments were found. The same types of nuclei were found in pollen tubes that had entered the embryo sac and their fusion with the female nuclei could be observed. Largely as a consequence of the differences in type of the male chromatin, the following different types of fertilization were observed, ( a) Both the egg nucleus and the polar nuclei are fertilized by sperm chromatin from one or two pollen tubes, ( b) Fertilization of only the egg nucleus or only the polar nuclei occurs, the other of these two kinds of female nuclei remaining unfertilized. The following types were observed with respect to nuclear fusion, ( a) A normal fusion as in untreated material (1–500 kR). ( b) Nuclear fusion occurs but the normal changes in chromatin structure of the zygote nucleus do not occur (150–500 kR). Most of these nuclei do not divide, but a few do. ( c) Nuclear fusion does not occur but the male chromatin is appressed to the female nucleus, which may sometimes be stimulated to start DNA synthesis and division (150–500 kR).