Biosynthesis and Degradation of Glycine Betaine and Its Potential to Control Plant Growth and Development

Glycine betaine (N,N,N-trimethyl glycine, GB) plays an important role in the response of plants to abiotic stress, mainly hydric stress. The aim of this review is to gather information about biochemical processes in which glycine betaine is involved and their impact in plant growth and development. In plants, GB is synthesized by two choline oxidation steps: the first step is choline oxidation to betaine aldehyde (BA) catalyzed by choline monooxygenase, and the second step is BA oxidation to GB catalyzed by betaine aldehyde dehydrogenase which uses NAD(P)+ as coenzyme. In plants, GB synthesis takes place in chloroplast, peroxisome, and cytoplasm. There is scarce information about GB degradation routes in plants. The role of GB as osmolyte is well known, but only until recently, the participation of GB in several metabolic processes including regulation of gene expression, regulation of the concentration and activity of enzymes, and proper protein folding and association has been studied. GB plays a role in growth and development because it increases photosynthetic capacity and protects the thylakoid membrane and increases antioxidant enzymes activity and concentration. GB synthesis provokes changes in ethylene synthesis and increases expression of auxin responsive IAA gene levels. The modulation mechanisms mediated by GB are described in this work.