Glycinebetaine, γ-aminobutyric acid betaine and δ-aminovaleric acid betaine have been isolated from four commercially-produced seaweed extracts. A reliable proton magnetic resonance spectroscopic assay method for the estimation of all three compounds has been developed. High performance liquid chromatography using low wavelength ultra-violet light detection was found to be unsuitable for the analysis of betaines in seaweed extracts, even after partial purification by passage through columns of ion-exchange resin. A microbiological assay procedure was also utilised based on measuring the grov/th of Klebsiella pneumoniae produced by the addition of seaweed extracts to a medium with a growth-inhibitory concentration of sodium chloride. The concentrations of betaines found in the extracts when determined by the *H NMR spectroscopic method were too low to account for all of the anti-stress related effects reported for seaweed extracts after their application to plants. However, the microbiological assay results indicate that the extracts contain, in addition to betaines, other components which play a significant role in overcoming osmotically-induced growth Inhibition of K. pneumoniae.
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