Improved analytical methods for determination of nitrogenous stress metabolites occurring in Limonium species

Efficient and reliable high-performance liquid chromatographic procedures h ave been developed for metabolic analyses of amino acids, polyamines and be taines in Limonium species. The adaptive significance of accumulated low-mo lecular-mass nitrogenous compounds in dry or salt environments is under stu dy. HPLC profiles of dansylated water-soluble polyamines revealed 1,3-diami nopropane and tyramine as the most abundant amines in the species under stu dy whereas common aliphatic di- and polyamines (i.e., putrescine, spermidin e and spermine) were poorly represented as their free forms. Nevertheless a cylated conjugates of putrescine, 1,3-diaminopropane and spermidine were al so characterized, especially in L. vulgare, a halophytic salt marshes speci es. Direct derivatization of amino acids of the crude aqueous extracts with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate allowed efficient determin ations of most proteinic amino acids as well as non-proteinic ones such as ornithine, gamma-aminobutyric acid and beta-alanine also related to polyami ne metabolism. Analysis of betaines was improved, especially for beta-alani ne betaine, which is quite uncommon in higher plants whose metabolic routes from beta-alanine are poorly understood. beta-Alanine betaine was first co nverted to acrylic acid through trimethylamine beta-elimination under alkal ine treatment of the crude extracts and then quantified by HPLC. Thus Limon ium species ranged from high beta-alanine betaine accumulators, to low accu mulators and finally to a third group where it was not detected, since beta -alanine betaine was replaced by glycine betaine as shown here by H-1-NMR i nvestigations. Metabolic links between these nitrogenous solutes and the ad aptive significance of such adjustments are discussed. Special emphasis is directed towards the possible involvement of aliphatic polyamine oxidative catabolism, which seems to be effective in these species, to precursor recy cling for compatible solute biosynthesis. (C) 1999 Elsevier Science B.V. Al l rights reserved.