The effects of 2-thiouracil on growth and metabolism in the root - II. The metabolism of isolated root segments

Abstract

In this investigation the effect of 2-thiouracil on the metabolic changes occurring in isolated 2 to 4 mm subapical pea root segments were studied. 2-Thiouracil, in the presence of sucrose, increased the respiration rate of elongating segments, but had no effect on oxidative phosphorylation. The stimulation was sensitive to cyanide. During extension growth there were changes in the activities of invertase, acid-phosphatase and ribonuclease. 2-Thiouracil did not alter the course of enzyme development, but did increase the activities of all three enzymes. High concentrations of D-threo-chloramphenieol inhibited the development of the enzymes even in the presence of 2-thiouracil. 2-Thiouracil was incorporated into the RNA of all subcellular fractions, but to different extents and it also appears to be incorporated into a non-nucleotide fraction in the cell walk There was evidence that 2-thiouracil slightly increased the rate of incorporation of uridine into RNA . The incorporation of leucine into the proteins of all subcellular fractions was stimulated in the presence of 2-thiouracil. Incorporation of ( 14 C)-sucrose into the cell-wall polysaccharides during the period of maximum growth rate was greatly stimulated by 2-thiouracil and the evolution of respiratory 14 CO 2 was also stimulated by it. These observations are discussed in relation to other work.