Chlorophyll breakdown in senescent banana leaves: catabolism reprogrammed for biosynthesis of persistent blue fluorescent tetrapyrroles.
Bottom Line: Amazingly, in the leaves of banana plants, persistent hmFCCs were identified that accounted for about 80 % of the chlorophyll broken down, and yellow leaves of M. acuminata display a strong blue luminescence.The structures of eight hmFCCs from banana leaves were analyzed by spectroscopic means.As expressed earlier in related studies, the present findings call for attention, as to still elusive biological roles of these linear tetrapyrroles.
Affiliation: Institute of Organic Chemistry & Center for Molecular Biosciences, University of Innsbruck, 6020 Innsbruck (Austria).Show MeSH
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Mentions: Selective attachment of β-glucopyranosyl units via their anomeric center to the terminal oxygen of the hydroxyl-ethyl side chain at their 8-position is a typical feature of a variety of NCCs (X in Figure 12) and of some hmFCCs, as well. Indeed, the glycosidation observed in NCCs is (currently) presumed to already occur at the stage of the corresponding FCC precursors in the cytosol, where it would be catalyzed by still unidentified glycosidases.[8, 45] This type of glycosidation is reminiscent of the glucuronidation of bilirubine (in mammals), and has also been rationalized on the basis of the hypothetical requirements for the transport of FCCs into the vacuoles (where they isomerize to the corresponding NCCs). In contrast, esterification of FCCs by a gluco- or galactopyranosyl group at the critical propionate with the primary 6′-OH-group of the sugar units, as found here, provides sugar esters that may have (different) basic physiological roles: the sugar esters stabilize hmFCCs against their acid induced isomerization to NCCs (as also achieved, similarly, by a daucic acid residue), and they simultaneously provide linkers for attachment of further groups. Thus, (at least) two further types of hypothetical cytosolic enzymes are suggested, which wait for identification.
Affiliation: Institute of Organic Chemistry & Center for Molecular Biosciences, University of Innsbruck, 6020 Innsbruck (Austria).