The influence of copper on the metabolism of malic acid in intact barley roots

In experiments lasting for 2 and 24 h the content of malic acid in the root tips of barley plants (Hordeum distichon L. cv. Gerda BS) declined in higher concentration ranges of copper as well as with longer uptake periods. This was accompanied by falling activities of the NAD+‐linked malate dehydrogenase, the NADP+‐linked malic enzyme, and the fumarase in experiments lasting for 2 h, while under a duration of 24 h the activities of the NAD+‐linked malate dehydrogenase and the NADP+‐linked malic enzyme increased, and the activity of the fumarase decreased significantly if copper was studied in in vivo situation. The in vivo influence of copper on the activity of the malate synthase only led to slight changes. Therefore this enzyme might not contribute significantly to the changed content of malic acid, if copper was taken up.