Abstract
Previous work has provided evidence that plants may require boron to maintain adequate levels of pyrimidine nucleotides, suggesting that the state of boron deficiency may actually be one of pyrimidine starvation. Since the availability of pyrimidine nucleotides is influenced by their rates of synthesis, salvage, and catabolism, we compared these activities in the terminal 3 centimeters of roots excised from boron-deficient and -sufficient squash plants (Cucurbita pepo L.). Transferring 5-day-old squash plants to a boron-deficient nutrient solution resulted in cessation of root elongation within 18 hours. However, withholding boron for up to 30 hours 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. Boron deprivation had no significant effect on pyrimidine salvage or catabolism. These results provide evidence that boron-deficient plants are not starved for uridine nucleotides collectively. Whether a particular pyrimidine nucleotide or derivative is limiting during boron deprivation remains to be examined.
Highlights
'Supported by National Science Foundation Grant PCM 76-20594 and by an award from Sigma Delta Epsilon
Symptoms characteristic of boron deficiency can be induced by the addition of 6-azauracil or barbituric acid, known inhibitors of pyrimidine biosynthesis [13, 25, 26]
The hypothesis that boron is essential for maintaining adequate levels of pyrimidine nucleotides unifies several of the roles for boron reported in the literature
Summary
'Supported by National Science Foundation Grant PCM 76-20594 and by an award from Sigma Delta Epsilon Sherstnev and Razumova [29] reported decreased incorporation of ["4Cladenine into RNA of boron-deficient sunflower leaves and roots; while other workers have demonstrated increased incorporation of [14Cluridine [7] and [14CJorotic acid [36] into RNA in borondeficient mung bean root apices and cotton ovules, respectively These reports suggest that the utilization or the level of available purine or pyrimidine nucleotides, or both, is altered by boron deprivation. Intact plants and isolated organs cultured in the absence of boron were protected to varying degrees from developing boron deficiency symptoms when pyrimidine bases were added to the medium This result was taken as evidence that the state of boron deficiency may, be a case of pyrimidine starvation. We measured salvage activity for the reutilization of pyrimidines during these two states of boron nutrition
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