Pyrimidine salvage and catabolism in leaves of mangrove species

Abstract

We examined the metabolic fate of [2- 14C]uridine, [2- 14C]cytidine, [2- 14C]uracil and [2- 14C]dihydrouracil in leaf disks of Bruguiera sexangula in 0 mM or 250 mM NaCl. Uridine was readily converted to uracil nucleotides, and cytidine was converted to cytosine nucleotides and also uracil nucleotides, possibly after conversion to uridine. These nucleotides were utilised for synthesis of RNA and UDP-glucose 3 h after administration of labelled precursors. Degradation of uridine and cytidine was extremely limited. In contrast, salvage of [2- 14C]uracil was low, and up to 45% of uracil was degraded to CO 2. [2- 14C]Dihydrouracil, which is a possible intermediate in the reductive pathway of pyrimidine catabolism, was converted to β-ureidopropionic acid and CO 2. No inhibitory effect of 250 mM NaCl was apparent on pyrimidine metabolism of B. sexangula, although RNA synthesis was reduced slightly. The metabolic fate of [2- 14C]uridine was surveyed in seven other mangrove species, Bruguiera gymnorrhiza, Kandelia candel, Rhizophora stylosa, Sonneratia alba, Avicennia marina, Lumnitzera racemosa and Pemphis acidula. The general profile of [2- 14C]uridine in these mangrove leaves was similar to that in B. sexangula; almost all uridine was salvaged to nucleotides, UDP-glucose and RNA, and catabolism was very low. No or very little inhibitory effect of 250 mM NaCl on uridine salvage was found in leaf disks of mangrove species, except L. racemosa. A stimulatory effect of 250 mM NaCl on uridine salvage was found in P. acidula. In contrast, uptake and metabolism of [2- 14C]uridine, especially a salvage pathway, in the leaves of the non-halophyte plant Populus alba, were drastically impaired by 250 mM NaCl.