Mitotic Effects of Monochromatic Ultraviolet Radiation at 225, 265, and 280 nm on Eleven Stages of the Cell Cycle of the Grasshopper Neuroblast in Culture: 2. Changes in Progression Rate and Cell Sequence between the Stage Irradiated and Nuclear Membrane Breakdown

Abstract

Portions of embryos of the grasshopper, Chortophaga viridifasciata, were cultured in hanging drops under quartz cover slips. Immediately after exposure to 225, 265 or 280 nm radiation, microscope observations at 38.degree. C were begun. The morphologically identified stage and the time after treatment of selected neuroblasts were recorded at short-time intervals until prometaphase was reached. Mitotic retardation induced by irradiation of prereplication stages (metaphase, anaphase or early telophase) or S phase (middle or late telophase, interphase or very early prophase) is greatest in postreplication stages (early, middle and late prophase) and absent or minimal in stages morphologically identified as parts of S phase. UV irradiation superimposes on the normal diversity of progression rates an additional variation factor, so that cells do not necessarily reach prometaphase in the order of their sequence at the time of treatment. Caution is needed in ascribing particular radiosensitivities to substages of limited duration on the basis of the order in which they attain a subsequent stage.