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

AbstractColorless, non-fluorescent Chl-catabolites (NCCs) are the typical, ubiquitous products of chlorophyll (Chl)-breakdown in senescent leaves. However, a fluorescent Chl-catabolite (FCC) accumulated in de-greened leaves of Spathiphyllum wallisii (Peace Lily), which showed a weak blue luminescence. The FCC, named Sw-FCC-62, was ‘hypermodified’ with an unprecedented 6-(2-[3,4-dihydroxy-phenyl]-ethyl)-β-glucopyranosidyl ester at the propionyl group. Such esters stabilize FCCs against their typical and rapid, spontaneous isomerization to NCCs. Chl-breakdown in Sp. wallisii thus branches off from the ‘common’ path in leaves, and furnishes unique and ‘persistent’ FCCs. Our findings on ‘hypermodified’ FCCs also call for attention as to possible physiological roles of Chl-catabolites in plants

Cryptic chlorophyll breakdown in non-senescent green Arabidopsis thaliana leaves

Chlorophyll (Chl) breakdown is a diagnostic visual process of leaf senescence, which furnishes phyllobilins (PBs) by the PAO/phyllobilin pathway. As Chl breakdown disables photosynthesis, it appears to have no role in photoactive green leaves. Here, colorless PBs were detected in green, non-senescent leaves of Arabidopsis thaliana. The PBs from the green leaves had structures entirely consistent with the PAO/phyllobilin pathway and the mutation of a single Chl catabolic enzyme completely abolished PBs with the particular modification. Hence, the PAO/phyllobilin pathway was active in the absence of visible senescence and expression of genes encoding Chl catabolic enzymes was observed in green Arabidopsis leaves. PBs accumulated to only sub-% amounts compared to the Chls present in the green leaves, excluding a substantial contribution of Chl breakdown from rapid Chl turnover associated with photosystem II repair. Indeed, Chl turnover was shown to involve a Chl a dephytylation and Chl a reconstitution cycle. However, non-recyclable pheophytin a is also liberated in the course of photosystem II repair, and is proposed here to be scavenged and degraded to the observed PBs. Hence, a cryptic form of the established pathway of Chl breakdown is indicated to play a constitutive role in photoactive leaves