Tradescantia micronucleus bioassay and pollen tube chromatid aberration test for in situ monitoring and mutagen screening.

The meiotic pollen mother cells (PMC) of Tradescantia (spiderwort) are highly synchronized in their prophase I and tetrad stages. Chromosomes of this stage are sensitive to physical or chemical mutagens. Thus high frequency of acentric fragments or sticky chromosomes can be induced with very low level of mutagens. These induced chromosome aberrations become micronuclei (MCN) in the synchronized tetrads and they can be easily identified and scored. Based upon these features, the Tradescantia micronucleus bioassay was established. This bioassay involves the exposure of PMC in the young inflorescences of the plant cuttings to gaseous agents through diffusion, to liquid agent through absorption and dialysis from the stem to flower buds, or to radiation. The exposed samples are fixed in aceto-alcohol (1:3) and prepared into microslides by using the aceto-carmine squash method. Frequencies of MCN in a large population of synchronized tetrads are the indications of genetic damage caused by the agents. Mature pollen grains of Tradescantia are free cells which can be cultured in lactose-agar medium. The generative cells in the cultured pollen tubes can carry out mitosis similar to the in vivo condition. The G2 interphase chromosomes of pollen mitosis are highly sensitive to gaseous or liquid chemicals and radiation. Treatments can be applied to these mitotic generative cells of the mature pollen or the mitotic generative nuclei of the developing pollen tube. The mitotic chromosomes of the generative cells are allowed to proceed through mitosis in the culture medium and slides are prepared for metaphase figures. Frequencies of various types of chromatid aberrations can be scored and used as the indices of genetic damage.