Changes in polysome activity related to radiation-induced mitotic delay in synchronized root meristem cells

Earlier studies with synchronized plant cell populations suggested that radiation damage resulting ultimately in mitotic delay could be expressed either immediately or at some time after exposure. Whether damage resulted in an immediate cessation of progression through the mitotic cycle or whether cessation occurred latently was contingent on whether the protein requirements for further progression in the mitotic cycle were satisfied at the time of exposure. Experiments were designed to determine the effects of γ-rays on protein synthesis and whether a relationship existed between radiation-induced mitotic delay and changes in rate of protein synthesis of synchronous populations. The results obtained demonstrated that an elevated rate of protein synthesis following γ-irradiation is associated with mitotic delay. Elevated rates of polypeptide synthesis measured by sedimentation analysis, and protein synthesis measured autoradiographically, occurred only when irradiated populations were no longer making progress toward mitosis. The results suggested that: a) during mitotic delay an elevated rate of protein synthesis represents those proteins required for recovery; and b) that recovery occurs at the expense of further preparation for cycle progression, resulting in an impairment of division-oriented protein synthesis.