Growth and 2, 4-Diaminobutyric Acid Composition of Flatpea (Lathyrus sylvestris L.) as Influenced by Mineral- and Symbiotically Fixed-Nitrogen

Flatpea (Lathyrus sylvestris L. cv. ‘Lathco’) plants,grown hydroponically, were inoculated with rhizobia (Rhizobiumleguminosarum strain 92F2), supplied with nitrate nitrogen (2meq 1^–1), or provided with both rhizobia and . Nodulated plants supplied with had the highest biomass and the highest level of free amino acids in leavesand roots. Nitrogen fixation was depressed 80% in inoculatedplants supplemented with . Compared to plants whose nitrogen requirement was satisfied either partially orfully by , plants that were totally dependent upon biological nitrogen fixation had fewer lateral shoots andlower concentrations of nitrogen, soluble protein, and totalfree amino acids in the shoots, especially in the leaves. Thesymbiotic association between plants and rhizobia for nitrogenfixation was not essential to the production and accumulationof 2,4-diaminobutyric acid (A₂bu) and other non-protein aminoacids in flatpea. Levels of A₂bu, and most of the other freeamino acids quantified, were significantly lower in the nodulatedplants grown in the absence of than in the inoculated or noninoculated plants supplied with . Arginine and glutamic acid were exceptions in that levels ofthese two amino acids were higher in roots bearing effectivenodules. Plant responses to the different treatments are attributedto the amount of nitrogen available to the plant, rather thanthe method or form of nitrogen supplied. Key words: 2,4-Diaminobutyric acid, Lathyrus, nitrogen