INHIBITION OF MITOSIS IN PISUM ROOT MERISTEMS BY CONTINUOUS GAMMA RADIATION: THE INFLUENCE OF TEMPERATURE ON THE SYNTHESIS OF DNA, RNA AND PROTEIN DURING INHIBITION

Abstract

Tritiated precursors of DNA, RNA and protein were used to measure synthesis at 10 and 20C in root meristem cells of Pisum after they were mitotically arrested by continuous irradiation with gamma rays. The experiments were designed to determine if the arrested cells accumulated in a certain part of interphase, to determine the effect on DNA, RNA and protein synthesis, to find out if the effects were temperature dependent, and finally to reveal possible relationships between growth inhibition and altered synthesis. The results showed that the incorporation of DNA and RNA precursors was impaired by irradiation and that decreased temperature further increased radiation impairment of DNA synthesis. Protein synthesis on the other hand was not impaired by irradiation at either temperature. Irradiation at 20C reduced the number of DNA‐synthesizing cells; at 10C this number was reduced to near zero. Although irradiated cells synthesizing RNA showed a reduction in grain counts when compared to the controls, they still retained the ability to incorporate tritiated uridine at 10C. It was hypothesized that the combination of reduced DNA and RNA synthesis and unaffected protein synthesis resulted in precocious maturation of the arrested meristem cells. Growth which occurred in the absence of cell division was attributed to meristematic cells which precociously matured and cells which were in the region of elongation.