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Experiments with non-nodulated alfalfa (Medicago sativa L. cv. Europe) plants grown in hydroponic culture, were carried out to estimate the remobilization of nitrogen (N) reserves and to investigate the transported forms of reduced soluble-N in xylem during regrowth following shoot removal. Endogenous N remobilization were estimated by ^15N labelling and amino acids in xylem sap were analysed. The ^15N contents of regrowing leaves and stems increased as a result of remobilization of N reserves mainly from root system. Regrowing leaves were a stronger sink than regrowing stems, with about two-thirds of remobilized ^15N being recoved in leaves. Endogenous N in lateral roots accounted for about 46% of the total N reserves used for regrowth, while tap roots accounted for 23%. About 72% of total endogenous N remobilized to regrowing shoot, occurred during the first 10 days of regrowth. The outflow of reduced soluble-N (mainly amino acids) was greater than that of protein-N, while the latter was the largest storage pool in tap root and lateral roots. It is suggested that amino acids-N was the most readily avaiable form of N reserves. Asparagine, which represented about 75% of amino acids-N in xylem sap, was the main transported form of reduced N. Its relative contents, during the first 10 days of regrowth, decreased from 75% to 59%. This decline was accompanied by compensatory increase in the relative contents of asparatate and glutamine.
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