ABSTRACT
This chapter will consider the central role of amino acid metabolism in abiotic stress resistance of plants. We will attempt to highlight progress made since the last comprehensive review of this field by Stewart and Larher (1980). Major emphasis will be placed on the role of amino acid metabolism in the synthesis of compatible osmolytes. This class of molecules includes certain amino acids (notably proline). quaternary ammonium compounds (e.g.• glycinebetaine. prolinebetaine. p..alaninebetaine. and choline-O-sulfate). and the tertiary sulfonium compound 3-dimethylsulfoniopropionate (DMSP). The quaternary ammonium compounds and DMSP are derived from amino acid precursors. These compounds share the property of being uncharged at neutral pH and are of high solubility in water (Ballantyne and Chamberlin 1994). Moreover. at high concentrations they have little or no perturbing effect on macromolecule-solvent interactions (Yancey et aI. 1982; Low 1985; Somera 1986; Timasheff 1993; Yancey 1994). Unlike perturbing solutes (such as inorganic ions) that readily enter the hydration sphere of proteins. favoring unfolding. compatible osmolytes tend to be excluded from the hydration sphere of proteins and stabilize folded protein structures (Low 1985). These compounds are thought to play a pivotal role in plant cytoplasmic osmotic adjustment in response to osmotic stresses (Wyn Jones et aI. 1977).
