The greening process in cress seedlings. I. Pigment accumulation and ultrastructure after application of 5‐aminolevulinate and complexing agents

Abstract

A reduced rate of greening after continuous illumination was observed in dark‐grown cress seedlings (Lepidium sativum L.) incubated with 5‐aminolevulinate (ALA) or the complexing agents 2,2′‐bipyridyl, 8‐hydroxyquinoline or 1,10‐phenanthroline. This effect cannot be explained merely by photodynamic damage caused by chlorophyll precursors which are accumulated in the dark under these conditions. Flash light experiments revealed that photoconversion of protochlorophyll(ide) to chlorophyllide was not influenced by chelator treatment. The next step in the chlorophyll pathway, the esterification of chlorophyllide, however, was inhibited. Simultaneously applicated ALA and complexing agents did not result in a synergistic reponse; on the contrary, ALA seemed to render cress plants less susceptible to the treatment with complexing agents upon subsequent irradiation. Ultrastructural studies demonstrated that grana formation in light was inhibited after pretreatment with ALA or complexing agents.