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Articles

Relationship between Photoconvertible and Nonphotoconvertible Protochlorophyllides ¹

^a Department of Biology, Brandeis University, Waltham, Massachusetts 02154

Two forms of protochlorophyllide are found in dark-grown bean (Phaseolus vulgaris, var. Black Velentine) leaves, one (protochlorophyllide₆₅₀) which is directly photoconvertible to chlorophyllide and another (protochlorophyllide₆₃₂) which is not. Dark-grown leaves placed in solutions of -aminolevulinic acid accumulate protochlorophyllide₆₃₂. Protochlorophyllide₆₅₀ and protochlorophyllide₆₃₂ can be partially separated on sucrose density gradients. A nitrogen atmosphere blocks chlorophyll synthesis in light or the regeneration of protochlorophyllide₆₅₀ in the dark, even in the presence of excess -aminolevulinic acid, except when a stockpile of protochlorophyllide₆₃₂ is present in the leaf. Under the latter conditions chlorophyll synthesis or protochlorophyllide₆₅₀ regeneration is accompanied by a decrease in protochlorophyllide₆₃₂. These experiments suggest that protochlorophyllide₆₃₂ may be converted to protochlorophyllide₆₅₀.

Cycloheximide inhibited greening only after an "action-dependent" delay, requiring a predictable minimal period of illumination. This inhibition could be relieved for a time by feeding -aminolevulinic acid.

¹ Research supported in part by National Science Foundation Grant GB-16047 and in part by Developmental Biology Training Grant T1-HD-22 of the United States Public Health Service. This work represents part of a thesis presented by A. E. M. to the faculty of the Graduate School of Brandeis University in partial fulfillment of the requirements for the Ph.D. degree.