La synthèse de l'acide δ-aminolévulinique et de la chlorophylle lors de l'éclairement d' Euglena gracilis étiolées

Abstract

1. 1. Addition to greening Euglena of levulinic acid, a competitive inhibitor of δ-aminolevulinate dehydratase, temporarily stops chlorophyll synthesis and produces accumulation of δ-aminolevulinate. The amount of δ-aminolevulinate accumulated 30 min after inhibitor is stoichiometrically equivalent (within ± 10%) to the chlorophyll produced in control cells during the same time. 2. 2. In the presence of inhibitor, a small quantity of δ-aminolevulinate is produced by etiolated Euglena during growth in the dark. In greening Euglena returned to dark, the synthesis of δ-aminolevulinate is progressively abolished after 20 min. Thus, the synthesis of δ-aminolevulinate in Euglena shows an indirect dependence towards light. 3. 3. The observations lead to the recognition of at least three ways of control for the synthesis of δ-aminolevulinate and its precursors: one way is related to cellular growth in the dark, the second depends on active photosynthesis and may be blocked by 3(3,4-dichlorphenyl)-1,1-dimethylurea (DCMU), and the last, unimpaired by DCMU, depends on light but not on photosynthesis. This last way is effective at the beginning of greening, and is turned off before the end of the process. Besides, δ-aminolevulinate synthesis can be limited by factors related with the abundance and mobility of cellular reserves. 4. 4. Addition of δ-aminolevulinate does not increase the production of chlorophyll, except during the terminal phase of greening, when cellular reserves are nearly consumed. Thus, the synthesis of chlorophyll pigments seems to be regulated either by a limitation of δ-aminolevulinate precursors or by a limitation in the last stages of the synthesis, according to the stage of greening. In the latter case, a feedback control limits δ-aminovulinate production.