Can a high chlorophyllase activity bias the use of the phytyldiol versus phytol ratio (CPPI) for the monitoring of chlorophyll photooxidation in seawater?

The photodegradation rates of chlorophyll-a and phytol in both its esterified and free forms were followed in killed cells of Phaeodactylum tricornutum Bohlin, a diatom possessing a strong chlorophyllase activity. The Chlorophyll Phytyl side chain Photodegradation Index (CPPI), defined as the molar ratio of phytyldiol (a specific photoproduct of the phytyl chain) versus phytol, was used to estimate the chlorophyll-a photodegradation rate. Despite the strong chlorophyllase activity of this alga and the high photoreactivity of free phytol, the CPPI gave a good estimation of the chlorophyll-a photodegradation state. These estimates were good for the axenic and non-axenic incubations, since aerobic bacterial degradation processes act upon free phytyldiol and phytol without high selectivity.