Effect of short‐term salt stress on the metabolic profiles of pyrimidine, purine and pyridine nucleotides in cultured cells of the mangrove tree, <i>Bruguiera sexangula</i>

Abstract

To investigate the short‐term (3 h) effect of salt on the metabolism of purine, pyrimidine and pyridine nucleotides in mangrove ( Bruguiera sexangula ) cells, we examined the uptake and overall metabolism of radiolabelled intermediates involved in the de novo pathways and substrates of salvage pathways for nucleotide biosynthesis in the presence and absence of 100 m M NaCl. Uptake by the cells of substrates for the salvage pathways was much faster than uptake of intermediates of the de novo pathways. The activity of the de novo pyrimidine biosynthesis estimated by [2‐ 14 C]orotate metabolism was not significantly affected by the salt. About 20–30% of [2‐ 14 C]uridine, [2‐ 14 C]uracil and more than 50% of [2‐ 14 C]cytidine were salvaged for pyrimidine nucleotide biosynthesis. However, substantial quantities of these compounds were degraded to 14 CO 2 via β‐ureidopropionate (β‐UP), and degradation of β‐UP was increased by the salt. The activities of the de novo pathway, estimated by [2‐ 14 C] 5‐aminoimidazole‐4‐carboxamide ribonucleoside, and the salvage pathways from [8‐ 14 C]adenosine and [8‐ 14 C]guanosine for the purine nucleotide biosynthesis were not influenced by the salt. Most [8‐ 14 C]hypoxanthine was catabolised to 14 CO 2 , and other purine compounds are also catabolised via xanthine. Purine catabolism was stimulated by the salt. [ 3 H]Quinolinate, [carbonyl‐ 14 C]nicotinamide and [carboxyl‐ 14 C]nicotinic acid were utilised for the biosynthesis of pyridine nucleotides. The salvage pathways for pyridine nucleotides were significantly stimulated by the salt. Trigonelline was synthesised from all pyridine precursors that were examined; its synthesis was also stimulated by the salt. We discuss the physiological role of the salt‐stimulated reactions of nucleotide metabolism.