Betaine Lipids
Betaines are amino acid derivatives that have a fully methylated nitrogen atom (quaternary ammonium compounds). The three most well-known plant betaines are glycine, proline, and $-alanine betaines. Betaines are part of a larger class of compounds known as osmoprotectants. Osmoprotectants increase the osmotic pressure in the cytoplasm and stabilize proteins and membranes when salt levels are not optimal. Plant betaine levels typically rise when the plant is exposed to stressors such as increased salinity, decreased water levels, and low temperatures.
McNeil, S.; Nuccio, M.; Hanson, A. Betaines and Related Osmoprotectants. Targets for Metabolic Engineering of Stress Resistance. Plant Physiology. 1999,120, 945-949