NAD-Dependent and NADP-Dependent Alcohol Dehydrogenases in Escherichia coli

The isomeric ratio and level of natural xanthoxin (XAN) in tomato plants (Lycopersicon esculentum) were examined by a more reliable analytical method than has been reported before. Efforts were made to avoid artificial isomerization between c-XAN and t-XAN throughout the isolation, derivatization and GC-MS procedures. Natural XAN was separated from contaminating chlorophylls before rev. HPLC purification, derivatized to abscisic acid methyl ester (MeABA) in four chemical steps, and quantified with the deuterium-labeled internal standards on clear and reproducible full GC-EI-MS. It was revealed that the isomeric composition of natural XAN was exclusively shifted to c-XAN. The level of c-XAN was higher and more significantly induced by water stress in older plants. The significant role of c-XAN as an ABA biosynthetic precursor is suggested.