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Chloroplast Biogenesis 31

DETECTION OF AN INHIBITOR OF PROTOCHLOROPHYLL BIOSYNTHESIS IN CUCUMBER COTYLEDONS ¹

Laboratory of Plant Pigment Biochemistry and Photobiology, Department of Horticulture, University of Illinois, Urbana, Illinois 61801

An extract from cucumber cotyledons was shown to cause an inhibition of protochlorophyll biosynthesis and accumulation. The extract inhibited the net synthesis of protochlorophyll as well as the incorporation of -amino[¹⁴C]levulinic acid into protochlorophyllide and protochlorophyllide ester by excised cotyledons. The inhibition of -amino[¹⁴C]levulinic acid incorporation into the two protochlorophyll species was also observed in isolated etiochloroplasts before and after lysis of the plastids. The inhibition did not appear to involve the oxidation of the -aminolevulinic substrate or its translocation across the plastid membrane. Kinetic analysis of the rate of protochlorophyllide and protochlorophyllide ester biosynthesis in the presence and absence of the inhibitor suggested that the mode of inhibition of the two protochlorophyll species was different.

¹ This work was supported by Research Grant PCM 7811559 from the National Science Foundation and by funds from the Illinois Agricultural Experiment Station.