The Effects of Levulinic Acid and 4,6-Dioxoheptanoic Acid on the Metabolism of Etiolated and Greening Barley Leaves

Application of levulinic acid (LA), a competitive inhibitor of delta-aminolevulinic acid (ALA) dehydratase, to greening plant tissues causes ALA to accumulate at the expense of chlorophyll. 4,6-Dioxoheptanoic acid (DA), which has been reported to be an effective inhibitor of this enzyme in animal systems, has a similar but more powerful effect on ALA and chlorophyll metabolism in greening leaves of Hordeum vulgare L. var. Larker. Both LA and DA also inhibit the uptake of [(14)C]amino acids into etiolated and greening barley leaves and reduce their incorporation into protein. Treatment of etiolated and greening leaves with these compounds results in the inhibition of (14)CO(2) evolution from labeled precursors, including amino and organic acids. Inhibition of (14)CO(2) evolution by these compounds is more effective in greening leaves than in etiolated leaves when [4-(14)C]ALA or [1-(14)C]glutamate are employed as precursors. Both LA and DA also inhibit the uptake and increase the incorporation of (32)Pi into organophosphorus by etiolated barley leaves. These results indicate that LA and DA have more far-reaching effects upon plant metabolism than was previously believed.