MOLECULAR CHARACTERIZATION OF GLYOXALASE-I FROM A HIGHER-PLANT - UP-REGULATION BY STRESS

A cDNA, GLX1, encoding glyoxalase-I was isolated by differential scree ning of salt-induced genes in tomato. Glyoxalases-I and -II are ubiqui tous enzymes whose functions are not clearly understood. They may serv e to detoxify methylglyoxal produced from triosephosphates in all cell s. The protein encoded by GLX1 shared 49.4% and 58.5% identity with gl yoxalase-I isolated from bacteria and human, respectively. Furthermore , yeast cells expressing GLX1 showed a glyoxalase-I specific activity 20-fold higher than non-transformed cells. Both GLX1 mRNA and glyoxala se-I polypeptide levels increased 2- to 3-fold in roots, stems and lea ves of plants treated with either NaCl, mannitol, or abscisic acid. Im munohistochemical localization indicated that glyoxalase-I was express ed in all cell types, with preferential accumulation in phloem sieve e lements. This expression pattern was not appreciably altered by salt-s tress. We suggest that the increased expression of glyoxalase-I may be linked to a higher demand for ATP generation and to enhanced glycolys is in salt-stressed plants.