Plants from several families (Chenopodiaceae, Gramineae, Compositae) accumulate betaine (glycine betaine) in response to salt or water stress via the pathway: choline → betainal (betaine aldehyde) → betaine. Betaine accumulation is probably a metabolic adaptation to stress. Intact protoplasts from leaves of spinach ( Spinacia oleracea ) oxidized [ 14 C]choline to betainal and betaine, as did protoplast lysates. Upon differential centrifugation, the [ 14 C]choline-oxidizing activity of lysates sedimented with chloroplasts. Chloroplasts purified from protoplast lysates by a Percoll cushion procedure retained strong [ 14 C]choline-oxidizing activity (1-3 nmol/mg of chlorophyll per hr), although the proportion of the intermediate, [ 14 C]betainal, in the reaction products was usually higher than for protoplasts. Isolated chloroplasts also readily oxidized [ 14 C]betainal to betaine (20-100 nmol/mg of chlorophyll per hr). Light increased the oxidation of both [ 14 C]choline and [ 14 C]betainal by isolated chloroplasts ≈3-fold; this light-stimulation was abolished by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Similar results were obtained with another chenopod ( Beta vulgaris ) but not with pea ( Pisum sativum ), a species that accumulates no betaine. The chloroplast site for betaine synthesis in chenopods contrasts with the mitochondrial site in mammals.

Hanson, A. D., May, A. M., Grumet, R., Bode, J., Jamieson, G. C., & Rhodes, D. (1985). Betaine synthesis in chenopods: Localization in chloroplasts. Proceedings of the National Academy of Sciences, 82(11), 3678–3682.