UMP, the product of the de novo pyrimidine nucleotide biosynthetic pathway, is further phosphorylated by kinas- es to form UTP. Cytidine-5’-triphosphate (CTP) is formed by an amination of UTP. The activities of enzymes that participate the conversion of UMP to UTP are very high in plant cells (Hirose and Ashihara, 1984) and as a result, the level of uracil nucleotides is equilibrated in cells and tis- sues. UMP kinase and a non-specific nucleoside diphos- phate kinase have been characterized in plants as follows.