Chapter 29 - Osmolyte Diversity, Distribution, and Their Biosynthetic Pathways

Abstract

Many abiotic stresses trigger the biosynthesis of diverse low-molecular-weight organic solutes called osmolytes in many plants. This encompasses a variety of compounds like amino acids (notably proline), tertiary sulfonium (dimethylsulfoniopropionate (DMSP)) and quaternary ammonium compounds (e.g., glycine betaine, proline betaine (also known as stachydrine), β-alanine betaine, pipecolate betaine (also known as homostachydrine), hydroxypipecolate betaine and choline-O-sulfate, trigonelline (nicotinic acid betaine)), sugar alcohols (mannitol, sorbitol, pinitol), and others in many species. The quaternary ammonium compounds and also DMSP are derived from amino acid precursors. Multiple pathways exist for their biosynthesis in bacteria and higher plants and so, the regulation is highly complex. Biosynthetic pathways and the genes associated in the biosynthetic pathways of many osmolytes have been identified, validated in different plants for their role in abiotic stress tolerance. However, in many pathways, the pathway intermediates and the genes that encode the enzymes are still not known completely. It is believed that these osmolytes help the bacteria and plant systems to cope with abiotic stress through cellular osmotic adjustment and by scavenging reactive oxygen species. The diversity, occurrence, and myriad functions of osmolytes during plant growth and development are being unfolded slowly in many systems.