Haem synthesis during cytochrome P-450 induction in higher plants. 5-Aminolaevulinic acid synthesis through a five-carbon pathway in Helianthus tuberosus tuber tissues aged in the dark.

Chlorophyll and haem synthesis in illuminated Jerusalem artichoke tuber tissues were very efficiently inhibited by gabaculine (3-amino-2,3-dihydrobenzoic acid). This inhibition seems to be due specifically to a blockade of the pathway for 5-aminolaevulinate biosynthesis which used glutamate as a substrate (the so-called C5 pathway) since we could not detect any inhibition of protein synthesis in the treated tissues and there was no effect of gabaculine on the glycine-dependent yeast 5-aminolaevulinate synthase used as a model. In dark-aged artichoke tissues, gabaculine also effectively blocked cytochrome P-450 induction, peroxidase activity and 5-aminolaevulinic acid synthesis, thus suggesting the involvement of a C5 pathway in cytoplasmic and microsomal haemoprotein synthesis in this higher plant. Allylglycine and (2-amino-ethyloxyvinyl)glycine, two olefinic glycine analogues which are potential suicide inhibitors of pyridoxal phosphate enzymes, were also demonstrated to be effective blockers of chlorophyll synthesis in artichoke tuber and Euglena cells exposed to light.