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Abstract
The tetrapyrrolic chlorophyll catabolites (or phyllobilins, PBs) were analyzed in yellow fall leaves of the grape Chardonnay, a common Vitis vinifera white wine cultivar. The major fractions in leaf extracts of V. vinifera, tentatively assigned to PBs, were isolated and their structures elucidated. The dominant fraction is a dioxobilin‐type non‐fluorescent Chl‐catabolite of a previously observed type. Two less polar fluorescent PBs were characterized as a novel dioxobilin‐type fluorescent Chl‐catabolite with a bicyclo‐1′,6′‐glycosyl architecture, and its new fluorescent formyloxobilin‐type analogue. The discovery of persistent hypermodified fluorescent PBs with the architecture of bicyclo‐[17.3.1]‐PBs (bcPBs), suggests the activity of an unknown enzyme that forges the 20‐membered macroring at the tetrapyrrolic core of a fluorescent PB. bcPBs may play specific physiological roles in grapevine plants and represent endogenous anti‐infective agents, as found similarly for other organic bicyclo‐[n.3.1]‐1′,6′‐glycosyl derivatives.
Highlights
The fall colors of deciduous plants, and the seasonal breakdown of chlorophyll (Chl) in their leaves, have been a stunning biological puzzle until recently.[1]
In leaf extracts of Chardonnay plants grown in a vineyard in the province of Bozen, we found both, type I and type II PBs, and discovered two remarkably structured new representatives of “hypermodified” fluorescent PBs, as well.[2d,12a] The structures of both fluorescent PBs display the exceptional bridging bicyclo[17.3.1]-1’,6’-glycopyranosyl architecture, discovered in Ug-non-fluorescent Chl catabolites (NCCs)-53.[11f]. This finding helps to specify more closely the pathway of the new branch of Chl breakdown to bicyclo[17.3.1]-1’,6’-glycopyranosyl PBs and encourages considering a relevant role of the bcPBs in the endogenous defense against fungal and bacterial pathogens in the grapevine leaves
Vv-dioxobilin-type non-fluorescent Chl catabolites (DNCCs)-51 accounted for over 90 % of the Vv-PBs isolated from the preparative extract of V. vinifera leaves
Summary
The fall colors of deciduous plants, and the seasonal breakdown of chlorophyll (Chl) in their leaves, have been a stunning biological puzzle until recently.[1] During the last quarter of a century, breakdown of Chl has been studied intensively in higher plants,[1b,2] and the structures of a large number of tetrapyrrolic Chl catabolites, named phyllobilins (PBs),[3] were determined in senescent leaves and ripening fruit.[2d,4] Based on complementary chemical and biological investigations, Chl breakdown has been unraveled as following a common PaO/ phyllobilin pathway in higher plants (see Scheme 1).[2a,c,d] The first discovered natural PBs were colorless formyloxobilin-type non-fluorescent Chl catabolites (NCCs).[1b,2d,4a,5] Such colorless tetrapyrroles from Chl degradation accumulate in the vacuoles of senescent leaves.[2a] There, they are generated by acid-induced isomerization from their fleetingly existent precursors, the corresponding colorless (formyloxobilin-type) fluorescent Chl catabolites (FCCs).[2a,6] FCCs arise in the chloroplast in one of two C16-epimeric forms of “primary” FCCs (pFCC or epipFCC),[7] generated by reduction of the red Chl catabolite (RCC)[8] by a plant-specific RCC-reductase (RCCR).[2c,9] The typical further FCC-functionalization starts with an astounding hydroxylation of pFCCs at their saturated 32-position,[1b,2d] catalyzed by the hydroxylase TIC55.[10] Most of the subsequent further peripheral modifications, derived from the structures of [b] C. Oberhuber Laimburg Research Centre, Laimburg 6-Pfatten (Vadena) 39040 Auer (Ora), BZ (Italy)
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