The biosynthesis and metabolism of betaines in plants. III. Studies on the biosynthesis of precursors of glycinebetaine in seedlings of wheat (Triticum vulgare vill.).

The synthesis ofglycinebetaine may proceed by two possible routes: (a) by the stepwise methylation of glycine, with sarcosine and dimethylglycine as intermediates, or (b) by the stepwise methylation of ethanolamine to choline with subsequent oxidation of the latter base. In certain animal tissues there is abundant evidence of the formation of betaine by oxidation of choline, and this step would appear to be essential for the labilization of a methyl group of choline (Muntz, 1950). Since the work of Mann & Quastel (1937) and Bernheim & Bernheim (1938) who showed that rat-liver preparations are capable of oxidizing choline via betaine aldehyde to betaine, further investigation of the enzyme system has shown that the two components choline oxidase and betaine aldehyde oxidase are largely concentrated in the mitochondrial fractions ofrat liver (Williams, 1952 a, b). Although betaine is widely distributed in plants and occurs in high concentration in some families (Cromwell & Rennie, 1953b) little is known ofthe mode ofsynthesis and role ofthis compound in the metabolism of higher plants. Barrenscheen & Vfalyi-Nagy (1942) claim to have demonstrated a stimulation of betaine synthesis in homogenates of wheat seedlings to which glycine and methionine had been added, but repetition of these experiments in this laboratory failed to show any substantial conversion of glycine into betaine. In the present paper experiments are described in which possible precursors of betaine were infiltrated into leaves of Beta vulgari8 L. and Atriplex patula L. with the object of determining the path of betaine synthesis. Preliminary experiments carried out by Cromwell & Rennie (1953 a) on roots and leaves ofseedling plants of Beta vulgari8 from which homogenates were prepared seemed to show the presence ofan enzyme which oxidized added choline to betaine. However, subsequent work showed that the activity of these homogenates was due to bacterial action.