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Articles

Control of Lactate Dehydrogenase, Lactate Glycolysis, and -Amylase by O₂ Deficit in Barley Aleurone Layers ¹

Commonwealth Scientific and Industrial Research Organization, Division of Plant Industry, Canberra, A.C.T. 2601, Australia

After 4 days in an atmosphere of N₂, aleurone layers of barley (Hordeum vulgare L. cv Himalaya) remained viable as judged by their ability to produce near normal amounts of -amylases when incubated with gibberellic acid (GA₃) in air. However, layers did not produce -amylase when GA₃ was supplied under N₂, apparently because -amylase mRNA failed to accumulate.

When an 8-hour pulse of [U-¹⁴C]glucose was supplied under N₂ to freshly prepared aleurone layers, both [¹⁴C]lactate and [¹⁴C]ethanol accumulated; the [¹⁴C]lactate/[¹⁴C]ethanol ratio was about 0.3. Prior incubation of layers for 1 day under N₂ 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 N₂, whereas alcohol dehydrogenase activity (ADH) was high initially and rose by 60%. The responses of LDH and ADH activities to O₂ tension were dissimilar; when layers were incubated in various O₂/N₂ mixtures, LDH activity peaked at 2 to 5% O₂ whereas ADH activity was highest at 0% O₂. 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 O₂ 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.

¹ Supported in part by a Guggenheim Fellowship to A. D. H.

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