The Effects of Copper Nutrition and Developmental State on the Biosynthesis of Diamine Oxidase in Clover Leaves 1

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The biosynthesis of diamine oxidase (DAO; EC 1.4.3.6) in leaf blades of subterranean clover (Trifolium subterraneum L. cv Seaton Park) was followed by labeling whole plants with 14CO2. A pulse-chase experiment where DAO was immunoprecipitated with anti-DAO antibodies showed that only leaf primordia and the youngest emerged leaves were able to synthesize the enzyme. The amount of DAO in young leaves of clover grown with a range of Cu treatments was determined by its enzymic activity and by single radial immunodiffusion against anti-DAO antibodies; both parameters were highly correlated with the Cu concentration of the leaf. Further, anti-DAO antibodies reacted against apo-DAO prepared in vitro indicating that apo-DAO was absent from Cu-deficient leaves. These results suggest that the biosynthesis of DAO in young clover leaves is controlled by the Cu concentrations of the leaves. Poly(A) mRNA purified from leaf primordia and young emerging leaves of plants with either a high Cu or low Cu supply was translated in wheat germ and rabbit reticulocyte cell-free systems. No differences between the two Cu treatments could be seen in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of the translation products after fluorography. However, anti-DAO antibodies did not detect any DAO synthesized in vitro from either treatment.

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