Structures of chlorophyll catabolites in bananas (Musa acuminata) reveal a split path of chlorophyll breakdown in a ripening fruit.
The disappearance of chlorophyll is a visual sign of fruit ripening. Yet, chlorophyll breakdown in fruit has hardly been explored; its non-green degradation products are largely unknown. Here we report the analysis and structure elucidation of colorless tetrapyrrolic chlorophyll breakdown products in commercially available, ripening bananas (Musa acuminata, Cavendish cultivar). In banana peels, chlorophyll catabolites were found in an unprecedented structural richness: a variety of new fluorescent chlorophyll catabolites (FCCs) and nonfluorescent chlorophyll catabolites (NCCs) were detected. As a rule, FCCs exist only "fleetingly" and are hard to observe. However, in bananas several of the FCCs (named Mc-FCCs) were persistent and carried an ester function at the propionate side-chain. NCCs were less abundant, and exhibited a free propionic acid group, but functional modifications elsewhere. The modifications of NCCs in banana peels were similar to those found in NCCs from senescent leaves. They are presumed to be introduced by enzymatic transformations at the stage of the mostly unobserved, direct FCC-precursors. The observed divergent functional group characteristics of the Mc-FCCs versus those of the Mc-NCCs indicated two major "late" processing lines of chlorophyll breakdown in ripening bananas. The "last common precursor" at the branching point to either the persistent FCCs, or towards the NCCs, was identified as a temporarily abundant "secondary" FCC. The existence of two "downstream" branches of chlorophyll breakdown in banana peels, and the striking accumulation of persistent Mc-FCCs call for attention as to the still-elusive biological roles of the resulting colorless linear tetrapyrroles.
Institute of Organic Chemistry, University of Innsbruck, 6020 Innsbruck, Austria.
Simone
S
Moser
Thomas
T
Müller
Andreas
A
Holzinger
Cornelius
C
Lütz
Bernhard
B
Kräutler
D002734:Chlorophyll / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D005453:Fluorescence; D005638:Fruit / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D028521:Musa / Q000737:chemistry / Q000378:metabolism*; D010936:Plant Extracts / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013997:Time Factors; D014866:Waste Products
D010936:Plant Extracts; D014866:Waste Products; D002734:Chlorophyll