Abstract Pollen tube cultures of Tradescantia paludosa Anders. Sax clone-3 were grown on microslides coated with lactose agar medium (0.02% colchicine). They were incubated in an air-tight moist chamber for 18 h to obtain the metaphase chromosomes of the pollen tube generative nuclei. SO2 treatments were applied at the beginning of the germination stage, 7–10 min after sowing the pollen. A total of about 0.075 ppm of SO2 was used for the entire incubation period. SO2 gas was either generated by the reaction between K2S2O5 and HCl inside the chamber or obtained from diluting the gas from commercial SO2 gas (Matheson Gas Products) of known concentration through a gas dilution system. Full-grown cultures fixed in Gate's fluid and stained in Feulgen were made into permanent slides for aberration-rate determination. Year-round study of SO2 effect on chromosomes was made possible by using a GRO-LUX lamp (Sylvania) illuminated incubator, in winter, to promote mitotic activity of pollen culture. In these studies, SO2 enhanced chromatid aberration rates (average 46 breaks/100 cells) in the cultures grown from field or hot-house plants during 3 consecutive summers (1970–1972). There was a gradual decrease in the fall and a gradual increase in spring in both background and enhanced aberration rates. When summer pollen cultures from GRO-LUX lamp pre-conditioned (7–20 days) plants were treated with SO2 in the same chamber with those grown from summer hot-house plants, high rate (42 breaks/100 cells) of aberration was observed only in cultures from summer hot-house plants.