Regulated expression of three alcohol dehydrogenase genes in barley aleurone layers

Three genes specify alcohol dehydrogenase (EC 1.1.1.1.; ADH) enzymes in barley (Hordeum vulgare L.) (Adh 1, Adh 2, and Adh 3). Their polypeptide products (ADH 1, ADH 2, ADH 3) dimerize to give a total of six ADH isozymes which can be resolved by native gel electrophoresis and stained for enzyme activity.Under fully aerobic conditions, aleurone layers of cv Himalaya had a high titer of a single isozyme, the homodimer containing ADH 1 monomers. This isozyme was accumulated by the aleurone tissue during the later part of seed development, and survived seed drying and rehydration. The five other possible ADH isozymes were induced by O(2) deficit. The staining of these five isozymes on electrophoretic gels increased progressively in intensity as O(2) levels were reduced below 5%, and were most intense at 0% O(2).In vivo(35)S labeling and specific immunoprecipitation of ADH peptides, followed by isoelectric focusing of the ADH peptides in the presence of 8 molar urea (urea-IEF) demonstrated the following. (a) Aleurone layers incubated in air synthesized ADH 1 and a trace of ADH 2; immature layers from developing seeds behaved similarly. (b) At 5% O(2), synthesis of ADH 2 increased and ADH 3 appeared. (c) At 2% and 0% O(2), the synthesis of all three ADH peptides increased markedly.Cell-free translation of RNA isolated from aleurone layers, followed by immunoprecipitation and urea-IEF of in vitro synthesized ADH peptides, showed that levels of mRNA for all three ADH peptides rose sharply during 1 day of O(2) deprivation. Northern hybridizations with a maize Adh 2 cDNA clone established that the clone hybridized with barley mRNA comparable in size to maize Adh 2 mRNA, and that the level of this barley mRNA increased 15- to 20-fold after 1 day at 5% or 2% O(2), and about 100-fold after 1 day at 0% O(2).We conclude that in aleurone layers, expression of the three barley Adh genes is maximal in the absence of O(2), that regulation of mRNA level is likely to be a major controlling factor, and that whereas the ADH system of barley has strong similarities to that of maize, it also has some distinctive features.