Dynamics of Nucleotides in Plants Studied on a Cellular Basis

This chapter discusses nucleotide dynamics in the metabolic regulation and growth regulation of suspension cultured cells and describes metabolic pathways, their localization within a cell, and intracellular transport. In a plant tissue, only one carbamoylphosphate (CP)-sase is involved in both pyrimidine nucleotide and Arg synthesis. CMP and CDP are not produced by de novo syntheses; they are, however, obtained through the recycling of phospholipid precursors, such as CDPcholine and CDPdiacylglycerol. Salvage pathways play a major role in the utilization of exogenous nucleobases and nucleosides obtained after mobilization. It also helps in the reutilization of endogenous nucleobases and nucleosides obtained from nucleic acid and nucleotide turnover. This process may be important for cellular compartments lacking or with incomplete de novo pathways as the import of nucleosides or bases may be facilitated relative to the more polar nucleotides. The nucleotide pool changes within a cell can be divided into two main parts: (1) net pool changes as a consequence of new synthesis or degradation and consumption of nucleotides and (2) changes in the individual components without changes in the total nucleotide content. The chemical composition of nucleotides indicates that nucleotide synthesis is dependent on the phosphate, carbon, and nitrogen sources; their availabilities influence the rate of nucleotide synthesis and the size of nucleotide pools.