A₂bu composed 20-40% of total free amino acids in flatpea tissues and constituted 2-4% of the tissue dry weight. Higher concentrations of A₂bu were found in the leaves than in the roots. A₂bu concentration in leaves and stems increased slightly with plant age. Higher nitrogen availability increased the content of A₂bu in flatpea, a response accompanied by an increase in the contents of soluble protein and other nitrogenous compounds. When exogenous nitrogen supply was decreased, A₂bu levels decreased significantly. Rhizobium infection had no effect on the A₂bu production by flatpea. Ammonium was toxic to flatpea growth. Together with typical toxic symptoms, A₂bu elevation was observed in flatpea plants fed with ammonium. Water-deficit stress also elevated A₂bu content of flatpea. The elevation of A₂bu concentration in aerial tissues of flatpea under stress may not be high enough to decrease the value of flatpea as a forage. 4-Aminobutyric acid (Abu), homoserine (Hse), and asparagine (Asn) were the other major free amino acids in flatpea. As with A₂bu, levels of Hse were higher in the leaves than in the roots. The opposite was true for Abu and Asn. The concentration of Abu in the stems increased consistently with plant age. In response to stress conditions, Abu accumulated in flatpea, especially in stems and roots. Asn was the most prevalent free amino acid in the roots of flatpea. Asn levels in roots increased with plant age and accounted for the greatest portion of the increase in the free amino acid pool in the roots of plants subjected to the water stress or supplied with nitrogen in the form of ammonium ions. Levels of Hse in flatpea were changed little in response to the experimental treatments. Relative amounts of major amino acids in flatpea changed with respect to plant organs and experimental factors. If expressed as ratios, the resulting values suggest metabolic relationships. / Ph. D. / incomplete_metadata