Identification of Cherry and Hageman's "Compound XI" From Maize As Chelidonic Acid

Abstract

During examination of the nucleotide fraction of barley seedlings a compound that resembled an unidentified constituent of maize shoots-"compound XI" (Cherry and Hageman 1960;Cherry et al. 1961)-was found. The materials from barley and from maize have now been identified as chelidonic acid (4-oxopyran-2,6-dicarboxylic acid); this compound is present in a number of species of grasses (Table 1). In tissues and in extracts at pH values above 2 this strong acid exists mainly in an anionic form (cf. Miyamoto and Brochmann-Hanssen 1962) and is referred to below as chelidonate. Materials and MethodsBarley, maize, oats, and wheat (for details of species and varieties see Table 1) were grown in the dark at 25°C on screens over 0·2 mM CaS04 after sterilization with hypochlorite. Shoots and roots were collected when the former were 4---8 cm long.The aerial parts of pasture grasses growing after spring rains were kindly provided by Mr. J. H. Silsbury.Chelidonate was extracted from plant tissue (1-2 g) by blending for 1 min at maximum speed in a homogenizer (Buhler, Tubingen, Germany) with 50 ml of ethanol-acetic acid-water (200 : 1 : 199 by vol.). The suspension was centrifuged for 15 min at 2000 g. The supernatant fraction was filtered (Whatman No. 541 paper) and 30 ml of filtrate was passed through two 45-mm disks of anion-exchange paper (Whatman DE 20), without suction, in a filtration apparatus (Millipore Filter Corp., Bedford, Mass., U.S.A.). The disks were washed with 100 ml water and chelidonic acid (together with other strong acids) was eluted with 4N formic acid (5 X 2 ml); the residue after removal of solvent at 40°Cj15 mmHg was subjected to electrophoresis (Markham 1955) on Whatman No. 40 paper in 0'05M citrate (Tris, pH 4·2) at 26 Vjcm for 1 hr. Chelidonate bands from the plant extract and from an authentic sample (anodic migration c. 20 cm) were located by contact printing on reflex document paper with a low-pressure mercury lamp and were eluted with 7 ml water at 95-100°C. Spectra of the extracts and of blanks were recorded with a Unicam SP.700 spectrophotometer; cells of 2 cm light path were used and the concentration of chelidonate was calculated from extinction values at 270 miL and 313 miL (€270ml'-€313ml' = 1O·3x 10 3 in the conditions of this assay; final pH 4·5-5·5).