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

Abstract

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 alpha-amylases when incubated with gibberellic acid (GA(3)) in air. However, layers did not produce alpha-amylase when GA(3) was supplied under N(2), apparently because alpha-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.