An isozyme of betaine aldehyde dehydrogenase in barley.

Betaine aldehyde dehydrogenase (BADH) is an important enzyme for Gly betaine synthesis. We isolated two types of BADH cDNAs (BBD1 and BBD2) from barley. As BBD1 contained the signal sequence (SKL) targeting to microbodies, BBD2 was more similar to previously reported genes coding for BADH in dicotyledons (chloroplast type) than those in monocotyledons (microbody type). The two barley BADH genes showed different expression patterns. The BBD1 transcript was more abundant in roots than leaves and was induced to higher levels 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 purified both enzymes and determined their N-terminal sequences. Based on comparisons of the N-terminal sequences to their deduced amino acid sequence, neither 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 chloroplasts or mitochondria.