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.
Folly
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Institut für Organische Chemie der Universität Fribourg, Ch. du Musée 9, CH-1700 Fribourg, Switzerland.
Engel
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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