Chloroplast biogenesis. Net synthesis of protochlorophyllide from protoporphyrin IX by developing chloroplasts.

Developing chloroplasts were isolated from greening Cucumis cotyledons in a co-factor-enriched medium and were incubated in the dark with 14C-labeled and unlabeled protoporphyrin IX. The metabolic pools between protoporphyrin and protochlorophyllide were monitored spectrofluorometrically. The incorporation of the 14C label into protochlorophyllide was also determined. It was shown that protoporphyrin IX, a postulated intermediate of the chlorophyll biosynthetic pathway, was convertible into protochlorophyllide. Since protochlorophyllide is the immediate precursor of chlorophyll a it was concluded that protoporphyrin IX was indeed an intermediate of the chlorophyll biosynthetic pathway.