Uracil as one of the multiple sources of β-alanine in Limonium latifolium, a halotolerant β-alanine betaine accumulating Plumbaginaceae

Abstract

The metabolic origin of β-alanine has been assessed in Limonium latifolium, a halotolerant Plumbaginaceae, which accumulates β-alanine betaine as an osmoprotectant. It was already known that β-alanine may act as a substrate for β-alanine betaine synthesis in this species and that propionate and spermidine metabolism may serve as putative ways for β-alanine production. The present study reveals that feeding experiments with substrates suspected to be converted to β-alanine bring about preliminary evidences about the multiplicity of the biosynthetic routes leading to this amino acid in L. latifolium. β-Alanine level is shown to be enhanced in roots from hydroponically grown seedlings fed with 1,3-diaminopropane, propionate or N-carbamyl β-alanine. Such precursor–product relationships were only observed in roots. Radiotracer experiments with [5,6- 3H]-uracil supplied to seedlings of L. latifolium and L. sinuatum, a β-alanine betaine non-accumulating species, demonstrate the effectiveness of uracil degradative pathway in β-alanine synthesis via dihydrouracil and N-carbamyl β-alanine in both species. It is demonstrated that this pathway is actually extended to β-alanine betaine only in the betaine accumulating species. The present results suggest that multiple ways deriving from aliphatic polyamines, propionate or uracil may cooperate for β-alanine and β-alanine betaine production in L. latifolium, the contribution of pyrimidine catabolism being highlighted for the first time.