Control of Lactate Dehydrogenase, Lactate Glycolysis, and α-Amylase by O2 Deficit in Barley Aleurone Layers

After 4 days in an atmosphere of N 2 , aleurone layers of barley ( Hordeum vulgare L. cv Himalaya) remained viable as judged by their ability to produce near normal amounts of α-amylases when incubated with gibberellic acid (GA 3 ) in air. However, layers did not produce α-amylase when GA 3 was supplied under N 2 , apparently because α-amylase mRNA failed to accumulate. When an 8-hour pulse of [U- 14 C]glucose was supplied under N 2 to freshly prepared aleurone layers, both [ 14 C]lactate and [ 14 C]ethanol accumulated; the [ 14 C]lactate/[ 14 C]ethanol ratio was about 0.3. Prior incubation of layers for 1 day under N 2 changed this ratio to about 0.8, indicating an increase in the relative importance of the lactate branch of glycolysis. l(+)Lactate dehydrogenase (LDH) activity was low in freshly prepared aleurone layers and increased 10-fold during 2 days under N 2 , whereas alcohol dehydrogenase activity (ADH) was high initially and rose by 60%. The responses of LDH and ADH activities to O 2 tension were dissimilar; when layers were incubated in various O 2 /N 2 mixtures, LDH activity peaked at 2 to 5% O 2 whereas ADH activity was highest at 0% O 2 . The LDH activity was resolved into several enzymically active bands by native polyacrylamide gel electrophoresis. We conclude that barley aleurone layers are highly adapted to O 2 deficiency, that they possess an inducible LDH system as well as an ADH system, and we infer that the LDH and ADH systems are independently regulated.