Chlorophyll b to chlorophyll a conversion precedes chlorophyll degradation in Hordeum vulgare L.
This study reveals by in vivo deuterium labeling that in higher plants chlorophyll (Chl) b is converted to Chl a before degradation. For this purpose, de-greening of excised green primary leaves of barley (Hordeum vulgare) was induced by permanent darkness in the presence of heavy water (80 atom % (2)H). The resulting Chl a catabolite in the plant extract was subjected to chemical degradation by chromic acid. 3-(2-Hydroxyethyl)-4-methyl-maleimide, the key fragment that originates from the Chl catabolite, was isolated. High resolution (1)H-, (2)H-NMR and mass spectroscopy unequivocally demonstrates that a fraction of this maleimide fragment consists of a mono-deuterated methyl group. These results suggest that Chl b is converted into Chl a before degradation. Quantification proves that the initial ratio of Chl a:Chl b in the green plant is preserved to about 60-70% in the catabolite composition isolated from yellowing leaves. The incorporation of only one deuterium atom indicates the involvement of two distinguishable redox enzymes during the conversion.
Institut für Organische Chemie der Universität Fribourg, Ch. du Musée 9, CH-1700 Fribourg, Switzerland.
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D002734:Chlorophyll / Q000737:chemistry* / Q000378:metabolism*; D000077194:Chlorophyll A; D003624:Darkness; D017666:Deuterium Oxide; D001467:Hordeum / Q000378:metabolism*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D018515:Plant Leaves / Q000378:metabolism; D018629:Spectrometry, Mass, Secondary Ion
D002734:Chlorophyll; C037184:chlorophyll b; D017666:Deuterium Oxide; D000077194:Chlorophyll A