BIOLOGICALLY MEDIATED DEFUNCTIONALIZATION OF CHLOROPHYLL IN THE AQUATIC ENVIRONMENT .1. SENESCENCE DECAY OF THE DIATOM PHAEODACTYLUM-TRICORNUTUM

To obtain further information about the origin of sedimentary tetrapyr roles such as the alkyl porphyrin desoxophylloerythroaetioporphyrin, t he defunctionalization of chlorophyll a has been studied in batch cult ures of the marine diatom Phaeodactylum tricornutum, which were induce d to undergo senescence by the exclusion of light. Identification of p igments by combined reversed phase high-performance liquid chromatogra phy-mass spectrometry (LC-MS), with on-line photo-diode array detectio n, revealed conversion of chlorophyll a to phaeophytin a and pyrophaeo phorbide a. The results demonstrate that certain chlorophyll a transfo rmation products which occur commonly in aquatic sediments can be form ed in part by the action of algal enzymes in the water column. The stu dy provides the first unambiguous identification of pyrophaeophorbide a during senescence of a non-mutant alga.