Decreased and increased expression of the subunit CHL I diminishes Mg chelatase activity and reduces chlorophyll synthesis in transgenic tobacco plants

verfasst von

Jutta Papenbrock, Erhard Pfündel, Hans Peter Mock, Bernhard Grimm

Abstract

The chelation of Fe²⁺ and Mg²⁺ ions forms protoheme IX and Mg-protoporphyrin IX, respectively, and the latter is an intermediate in chlorophyll synthesis. Active magnesium protoporphyrin IX chelatase (Mg-chelatase) is an enzyme complex consisting of three different subunits. To investigate the function of the CHL I subunit of Mg-chelatase and the effects of modified Mg-chelatase activity on the tetrapyrrole biosynthetic pathway, we characterized N. tabacum transformants carrying gene constructs with the Chl I cDNA sequence in antisense and sense orientation under the control of the CaMV 35S promoter. Both elevated and diminished levels of Chl I mRNA and Chl I protein led to reduced Mg-chelatase activities, reflecting a perturbation of the assembly of the enzyme complex. The transformed plants did not accumulate the substrate of Mg-chelatase, protoporphyrin IX, but the leaves contained less chlorophyll and possessed increased chlorophyll(a/b) ratios, as well as a deficiency of light-harvesting chlorophyll binding proteins of photosystems I and II. The expression and activity of several tetrapyrrolic enzymes were reduced in parallel to lower the Mg-chelatase activity. Consistent with the lower chlorophyll contents, the rate-limiting synthesis of 5-aminolevulinate was also decreased in the transgenic lines analyzed. The consequence of reduced Mg-chelatase on early and late steps of chlorophyll synthesis, and on the organization of light harvesting complexes is discussed.

Organisationseinheit(en)

Institut für Botanik
Institut für Pflanzengenetik

Externe Organisation(en)

Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK)
Julius-Maximilians-Universität Würzburg

Typ

Artikel

Journal

Plant Journal

Band

22

Seiten

155-164

Anzahl der Seiten

10

ISSN

0960-7412

Publikationsdatum

01.04.2000

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Genetik, Pflanzenkunde, Zellbiologie

Elektronische Version(en)

https://doi.org/10.1046/j.1365-313X.2000.00724.x (Zugang: Unbekannt)