Chromosome Aberrations in Calcium-deficient Tradescantia produced by Irradiation

Abstract

THE lack of calcium in Tradescantia microspores and in barley seeds has been demonstrated to increase the frequency of X-ray-induced chromosome aberrations above similarly irradiated material grown with optimal calcium^1,2. Mechanisms by which the lack of calcium could cause such an effect have been discussed¹. It is necessary to distinguish between two important alternatives: (1) does the absence of calcium confer a unique instability on chromosomes as observed by increased breakage, or (2) is the mechanism of increasing breakage more indirect ? A likely possibility in the latter category could involve low or high viscosity of the nucleoplasm. Calcium, potassium, sodium, magnesium and manganese are reported to influence viscosity to various degrees³. If the increased chromosome sensitivity to radiation acts by a change in viscosity, then metals other than calcium should have similar effects. Previously, magnesium and manganese have been shown to have no effect on modifying the frequency of chromosome aberrations by X-rays¹. Sodium is not usually an essential element in plants. Potassium is considered here in experiments with Tradescantia.