Synthesis, Salvage, and Catabolism of Uridine Nucleotides in Boron-Deficient Squash Roots

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Abstract
Previous work has provided evidence that plants may require B to maintain adequate levels of pyrimidine nucleotides, suggesting that the state of B-deficiency may actually be one of pyrimidine starvation. Since the availability of pyrimidine nucleotides is influenced by their rates of synthesis, salvage and catabolism, these activities were compared in the terminal 3 cm of roots excised from B-deficient and -sufficient squash plants (C. pepo L.). Transferring 5-day-old squash plants to a B-deficient nutrient solution resulted in cessation of root elongation within 18 h. However, withholding B for up to 30 h did not result in either impaired de novo pyrimidine biosynthesis or a change in the sensitivity of the de novo pathway to regulation by end product inhibition. B deprivation had no significant effect on pyrimidine salvage or catabolism. These results provide evidence that B-deficient plants are not starved for uridine nucleotides collectively. Whether a particular pyrimidine nucleotide or derivative is limiting during B deprivation remains to be examined.