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Seeds of Pisum sativum L. cv Finale and Lathyrs odoratus L. cv Spencer were germinated asepticafly in moistened sand in the dark. At several stages, the amino acid composition of the exudate and of the corresponding roots was analyzed. A number of common amino acids, including homoserine, were exuded by the growing seeding root in an early stage and were partly reabsorbed later. A number of uncommon amino acids, including several isoxazolin-5-one derivatives, uracil alanines, ia-yglutamyl-D-alanine, and a-aminoadipic acid were exuded at different rates.The range of compounds exuded by the roots of higher plants includes sugars, amino acids, enzymes, vitamins, nucleotides, growth hormones, terpenoids, flavanones, organic acids, and inorganic ions (22,24). By means of these exudates, the plants can affect the microflora in the rhizosphere by selective stimulation or inhibition of certain bacteria, fungi, or nematodes. There is also evidence that the root exudates of some plants inhibit the germination of some seeds or are toxic to roots of neighboring plants (22). It is generally believed that this root exudation is an uncontrolled process caused by damage to the cells at the root cap, at the sites where lateral roots emerge, and by infection of the root by microorganisms (23).Pea root exudates have been investigated in several laboratories (1,2,5,20,21,25). Some authors mentioned the presence of unknown amino acids (1,2,25). Rovira (20) showed the presence of UV-absorbing substances in 10-d-old and 21-d-old pea root exudates. Fries and Forsman (5) found some low mol wt UVabsorbing substances in the exudate from excised pea roots, besides adenine, guanine, uridine, and cytidine.A group of heterocyclic products, mostly amino acids, was isolated in our laboratory from pea seedlings and sweet pea seedlings: the uracil alanines willardiine and isowillardiine (15) and eight derivatives of the isoxazolin-5-one ring (13). (See Fig. 1 for the chemical structures.) Possibly, these products are the unknown compounds mentioned earlier by other authors (1, 2, 25).A preliminary study has shown the presence of some of these heterocycic products in root exudates of both pea and sweet pea seedlings (11). The differences in amino acid composition of the exudate and the corresponding root extract suggest that in some cases this exudation may be a specific phenomenon. This paper presents more detailed information on the exudation ofisoxazolin-5-one derivatives and other amino acids by intact roots ofetiolated pea and sweet pea seedlings under axenic conditions. MATERIALS AND METHODS Culture Conditions. Pea (Pisum sativum L. cv Finale) and sweet pea (Lathyrus odoratus L. cv Spencer) seeds were surface-sterilized with ethanol and were washed thoroughly with sterile distilled H20. After imbibing in sterile H20 for 16 h, the seeds were germinated in individual autoclaved glass tubes (20 x 2.8 cm), containing sterile quartz sand (5-cm height) moistened with distilled H20. The tubes were incubated at 25°C in the dark.Preparation...

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Various ways to substitute the nitrogen atom of isoxazolin-5-one are described. The properties of synthetic 2-substituted 3.4-unsubstituted isoxazolin-5-ones are compared with the natural compounds. The structure of the natural 2-(2-cyanoethyl)-3-isoxazolin-5-one has been proven by establishing its identity with the synthetic compound.A NUMBER of 2-substituted 3,4-unsubstituted isoxazolin-5-ones have been isolated from Pisum sativum and Lathyrus odoratus ~eedlings.l-~ They are the only known natural compounds with an isoxalin-&one ring. The confirmation of their chemical structure by synthesis was therefore desirable. Isoxazolin-5-one was first mentioned as a reaction product arising from nucleic acids by treatment with hydro~ylamine.~*~ Its synthesis and properties were described by De Sarlo? and on alkylation with diazomethane it gave 2-methyl-3isoxazolin-&one. This paper reports other ways to alkylate the nitrogen atom of isoxazolin-5-0ne.~ RESULTS AND DISCUSSIOKThe isoxazolin-5-one anion (1) was alkylated by ally1 bromides, dialkyl sulphates and toluene-$-sulphonates. Cyanoethylation of isoxazolin-5-one (1) was achieved with acrylonitrile. Only strong alkylating agents could substitute the isoxazolin-5-one anion (1). Dialkyl sulphates react readily, while toluene-p-sulphonates react rather slowly. Alkyl iodides, ethyl chloroacetate, and

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