PLANT PHYSIOLOGY , Vol 103, Issue 1 191-196, Copyright © 1993 by American Society of Plant Biologists
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MOLECULAR BIOLOGY AND GENE REGULATION |
The Circadian Oscillator Coordinates the Synthesis of Apoproteins and Their Pigments during Chloroplast Development
J. Beator and K. Kloppstech
Institut fur Botanik, Universitat Hannover, Herrenhauser Strasse 2, 3000 Hannover 21, Germany
Greening has been studied at circadian times of maximal and minimal levels
of mRNA for the light-harvesting chlorophyll a/b binding protein in
photosystem II (Cab mRNA) after circadian synchronization of etiolated
barley plantlets (Hordeum vulgare cv Apex) by heat-shock treatments. It was
found that greening occurs faster and without a lag period when
illumination was started at the time of maximal Cab mRNA accumulation. This
holds true for the rate of accumulation of Cab and early light-inducible
protein mRNAs, the levels of their correspondent proteins, and the levels
of chlorophyll a and b. When illumination was started at the time of Cab
mRNA minimum, a lag in the appearance of all components mentioned above was
observed. Under these conditions, the lag in chlorophyll b accumulation was
by far more pronounced than that found for chlorophyll a. The circadian
oscillation in the capacity of chlorophyll synthesis appears to be
controlled via [delta]-aminolevulinic acid ([delta]-ALA) synthesis.
[delta]-ALA accumulation after levulinic acid treatment is itself under
circadian control; the maxima in stationary concentrations coincide with
those of Cab mRNA levels. The amounts of protochlorophyllide and
photoconvertible protochlorophyllide showed only minor differences between
circadian minima and maxima, the levels being slightly lower during the
time of minimum.
