Influence of drought on the concentration and distribution of 2,4-diaminobutyric acid and other free amino acids in tissues of flatpea (Lathyrus sylvestris L.)

2,4-Diaminobutyric acid (A₂bu) may be responsible for the apparent toxicity of flatpea (Lathyrus sylvestris L.) forage to some livestock. To obtain information relative to environmental regulation of A₂bu, 3-month old flatpea plants, cv. “Lathco”, were subjected to water-deficit stress for 1, 2, and 4 weeks. A₂bu, the most abundant free amino acid in roots, stems, and leaves, increased nearly 100% in roots of stressed plants. Increases in the concentrations of asparagine (Asn), proline (Pro), and arginine (Arg) occurred in roots; Asn, Pro, and 4-aminobutyric acid (Abu) in stems; and Pro and homoserine (Hse) in leaves also occurred in response to drought stress. Proline was a minor constituent of the free amino acid pool, even under water-deficit stress. The distribution of A₂bu and Pro in the stressed plants (roots > stems > leaves) was the reverse of that in plants supplied with adequate water (roots < stems < leaves). As concentrations of Asn and Abu decreased from roots to leaves in control tissues, concentrations of Hse and A₂bu increased in roughly the same proportions. This observation suggests that Abu and Asn may be precursors of A₂bu and Hse, respectively. The increase in A₂bu levels in aerial parts of drought-stressed flatpea plants is probably not sufficient to lower the feed value of the forage.