Chlorophyll Catabolites – Chemical and Structural Footprints of a Fascinating Biological Phenomenon

Abstract

Twenty years ago, the molecular basis for the seasonal disappearance of chlorophyll was still enigmatic. In the meantime, our knowledge on chlorophyll breakdown has grown considerably. As outlined here, it has been possible to decipher the basic transformations involved in natural chlorophyll breakdown by identification of chlorophyll catabolites in higher plants, and with the help of the synthesis of (putative) catabolic intermediates. In vascular plants, chlorophyll breakdown typically converts the green plant pigments efficiently into colorless and non-fluorescent tetrapyrroles. It involves colored intermediates only fleetingly and in an (elusive) enzyme-bound form. The non-fluorescent chlorophyll catabolites accumulate in the vacuoles of degreened leaves and are considered the products, primarily, of a detoxification process. However, they are effective antioxidants, and may thus also have physiologically beneficial chemical properties.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Fluorescent chlorophyll catabolites in bananas light up blue halos of cell death

“…Indeed, NCCs, the often abundant final products of natural chlorophyll breakdown (2,6), are noteworthy antioxidants (6,28), which may help retain and extend the viability of ripe and senescing tissues. While specific physiological roles of NCCs in plants are still unknown, the related linear tetrapyrrole from heme breakdown, bilirubin, has recently attracted interest as cyto-protectant in mammals (29).…”

“…Their natural remains, which have only lately been identified (see Fig. 1) (2,28,(31)(32)(33), may now help explore crucial life processes in plants, in the microscopic, cellular domain.…”

Hypermodified Fluorescent Chlorophyll Catabolites: Source of Blue Luminescence in Senescent Leaves

“…[4,7] In contrast, fluorescent chlorophyll catabolites (FCCs) [5] accumulate in senescent, yellow banana leaves, and NCCs occur only in traces in their extracts ( Figure 1 and Figure S1 in the Supporting Information). Indeed, FCCs (such as pFCC) were observed earlier in senescent leaves, but only as short-lived precursors of NCCs.…”

“…These unique tetrapyrroles carry complex ester functions at the propionyl side chain and have turned up, so far, in ripening or senescent parts of the banana plant (for a second new case, see below). [5,10,13] The presence of ester functions at the propionyl side chain in the "persistent" Ma-FCCs explains the stunning lack of NCCs in the extracts of the banana leaves (see Figure S1 in the Supporting Information), since a free propionic acid function is required for the rapid formation of NCCs from FCCs by a stereoselective, acid-catalyzed isomerization. [9,12] While there is no precedence for an esterification of a chlorophyll catabolite with a (di)galactosyl unit, as observed here for Ma-FCC-61, related chlorophyll analogues occur in the coccolithophore Emiliana huxleyi.…”

A novel blue fluorescent chlorophyll catabolite accumulates in senescent leaves of the peace lily and indicates a split path of chlorophyll breakdown

“…An NCC fraction (Sw-NCC-58) was isolated similarly. Two less abundant other fractions, an FCC (Sw-FCC-66) and an NCC (Sw-NCC-51) were identified tentatively by their UV-and fluorescence spectra [15,16]. The fraction containing Sw-FCC-62 was concentrated to 3 ml under reduced pressure and re-purified by HPLC, using the solvent system described above.…”