An isozyme of betaine aldehyde dehydrogenase in barley

Betaine aldehyde dehydrogenase (BADH) is an important enzyme for Gly betain e synthesis. We isolated two types of BADH cDNAs (BBD1 and BBD2) from barle y. As BBD1 contained the signal sequence (SKL) targeting to microbodies. BB D2 was more similar to previously reported genes coding for BADH in dicotyl edons (chloroplast type) than those in monocotyledons (microbody type). The two barley BADH genes showed different expression patterns. The BBD1 trans cript was more abundant in roots than leaves and was induced to higher leve ls by salt, drought and abscisic acid (ABA) treatment. BBD2 transcript was more abundant in leaves and induced by salt, drought, PEG and ABA treatment . To understand the processing of these BADH proteins, we partially purifie d both enzymes and determined their N-terminal sequences. Based on comparis ons of the N-terminal sequences to their deduced amino acid sequence, neith er BBD1 nor BBD2 is processed at the N-terminus. These results suggest that BBD2 codes for a new type of BADH, which is not localized in either chloro plasts or mitochondria.