Identification of Catabolites of Chlorophyll-Porphyrin in Senescent Rape Cotyledons

Abstract

Developing shoots of rape seedlings (Brassica napus 1.) were excised and fed with 4-['4C]5-aminolevulinic acid to label the pyrroles in chlorophyll (Chl) synthesized during the final phase of expansion and greening of the cotyledons. About 80% of 14C taken up into the cotyledons was incorporated into Chl. The subsequent incubation of labeled shoots in permanent darkness caused the rapid loss of labeled Chl while increasing proportions of 14C appeared in the fradion of water-soluble compounds. Reversedphase high performance liquid chromatography resolved three nonfluorescent polar catabolites of Chl-porphyrin that were progressively accumulated as senescence advanced. At intermediate stages of senescence, the cotyledons contained a fluorescent radioadive derivative of Chl that was also detectable, together with traces of other putative fluorescent catabolites, in isolated senescent chloroplasts. l h e nonfluorescent catabolites, identified by means of radiolabeling, were also found to accumulate in attached cotyledons senescing under photoperiod; under these conditions, one of the compounds, NCC-1, was particularly abundant. The catabolites of rape exhibited the same ultraviolet spedra, characterized by a maximum at 320 nm, as a previously reported seco-

Chlorophyll Breakdown in Senescent Chloroplasts (Cleavage of Pheophorbide a in Two Enzymic Steps)

“…2; Table 11). Three fluorescent products could be identified as FCCs by their typical absorption maxima at 320 and 360 nm (Ginsburg and Matile, 1993;Mühlecker et al, 1997; data not shown). According to its retention time on HPLC, peak 2 was found to be identical to Bn-FCC-2, whereas the minor peak 3 corresponded to Ca-FCC-2, the first identifiable product of Pheide a cleavage in the presence of enzyme preparations from ripening fruits of C. annuum (Moser and Matile, 1997).…”

“…The red bilin depicted in Figure 1 was tentatively assumed to represent an intermediary catabolite of the Pheide a to FCC conversion . According to the nomenclature of Chl catabolites proposed by Ginsburg and Matile (1993), it was named RCC.…”

“…We hypothesize that this second step is catalyzed by the stroma protein required for in vitro conversion of Pheide a into the primary FCC. To test this hypothesis, a red bilin, RCC (for a nomenclature of Chl catabolites, see Ginsburg and Matile, 1993), was synthesized from Pheide a methyl ester (Krautflasks filled with tap water in permanent darkness for 4 and 6 d, respectively.…”

Gene expression during leaf senescence

“…Tbese compounds bave been designated nonfluorescent chlorophyll catabolites (NCCs). Tbis new terminology for chlorophyll catabolites is proposed in Ginsburg & Matile (1993). In senescent barley leaves tbe predominant NCC, RP 14, accumulates with time.…”

Stay‐green genotypes of Phaseolus vulgaris L.: chloroplast proteins and chlorophyll catabolites during foliar senescence

“…It turned out., however, that in their native form and if kept in a neutral solvent, these compounds are colourless and fluorescent . A nomenclature has recently been proposed (Ginsburg & Matile, 1993), according to which the fluorescent chlorophyll catabolites are designated as FCCs. The occurrence of FCCs concomitant with chlorophyll breakdown has been observed not only in Festuca (Duggelin et al 1988(7) but also in barley (Duggelin et aL, 19886) and rape (Ginsburg & Matile, 1993), By means of radiolabelling, two of the FCCs were confirmed as catabolites of chlorophyll (Matile, Schellenberg & Peisker, 1992;Ginsburg & Matile, 1993).…”