Amino acid contents and transport of fixed N in nodules of Leucaena leucocephala variety K-8

Seedlings of Leucaena leucocephala var. K-8 were grown with a N-free fertilizer or fertilizer containing 15N-depleted (NH4)2SO4 (0.01 atom 15N; 10 ppm). The nodules of 5 month old trees grown on N-free media were used for 15N-enriched treatment and as controls. Nodules from plants grown on 15N-depleted media were also used. Nodules were extracted with 0.5% aqueous toluene and aliquots were analyzed with a Beckman 120B Amino Acid Analyzer. Samples were separated into free ammonium, Asp-N, Glu-N, Asn and Gln amide- and amino-N, and remaining amino acids. Fractions were then analyzed for 15N content. Asn (27.3 umol/gfw) represented 56% of the total free amino acid pool in the nodules. Asn (amide-N and amino-N) also represented approximately 77% of the total N fixed during the one hour 15N-enriched N2 and the 15N-depleted treatments. Based on these findings and the fact that the ureide fraction is barely detectable in the nodules (0.25 μmol/gfw), the authors considers L. leucocephala an amide transporter of fixed N. Additional information will be presented on the amino acid contents of tissues, as well as a time course of amino acid content from seed through nodulation