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Articles

Photochlorophyll Biosynthesis in Cucumber (Cucumis sativus, L.) Cotyledons ¹

Paul A. Castelfranco^b

^a Department of Biological Sciences, Scientific and Agricultural Research Institute, Fanar, Lebanon, Department of Botany, University of California, Davis, California 95616

The formation of protochlorophyllide and protochlorophyllide phytyl ester was investigated during etioplast biogenesis in order to study the biosynthetic relation of these two compounds. Protochlorophyllide accumulates slowly during the first 2 days of germination, its rate of formation increases sharply during the 3rd day, and then it decreases. Protochlorophyllide phytyl ester starts accumulating a day later; its formation coincides with the initiation of xanthophyll biosynthesis. Kinetic analysis of specific radioactivities after ¹⁴C labeling of the protochlorophyll pools does not support the currently accepted conversion of protochlorophyllide into protochlorophyllide phytyl ester, but suggests that both compounds originate simultaneously from a common precursor pool.

¹ Supported in part by Research Grant GM-07532 from the United States Public Health Service.