The development of structure and function in chloroplasts of greening mutants ofScenedesmusIII. Biosynthesis ofδ-aminolevulinic acid

摘要

Cells of the mutant C-2A′ofScenedesmus obliquuswhich require light for chlorophyll formation were assayed for in vivo activity of ALA synthesis. In general, ALA and chlorophyll syntheses were coupled during the greening process. The action spectra for ALA and chlorophyll syntheses both show the highest activities in the blue region, but were different in details. Under certain conditions, ALA synthesis occurred without a corresponding synthesis of chlorophyll. Reasons for these variances were discussed.The controlling action of light on ALA synthesis may occur through three different, but related, mechanisms. The principle mechanism appeared to be linked to lightenhanced respiration since its inhibition by cycloheximide blocks ALA synthesis. The Hill coefficient of this inhibition is 2. After the light-induced enhancement of respiration had ceased, the Hill-coefficient of inhibition of ALA synthesis became 1. Thus, in addition to enhanced respiration, ALA formation depends on its sensitizing enzyme having a half-life time of less than 1 hr. Finally, the dependence of the synthesis of ALA precursors on light was eviden