On the 710 nm fluorescence emitted by the diatom Phaeodactylum tricornutum at room temperature

Abstract

The fluorescence emitted at 710 nm by Phaeodactylum tricornutum (F 710) was characterized. Development of F710 was found to be regulated by the quality of light needed for algal growth: weak red light absorbed mainly by Chl a induced its development, and weak blue-green light absorbed mainly by fucoxanthin and Chl c suppressed it. The difference spectra between cells grown under the two light conditions revealed two Chl a forms, absorption peaks of which were located at 692 nm (Chl a692) and at 703 nm (Chl a703), respectively, in red-light-grown cells. During cell growth under red light, the appearance and intensification of the emission correlated well with development of Chl a692 and Chl a703 suggesting that the two forms of Chl a are involved in the energy flow to F 710. A clear induction phenomenon characteristic of the PSII fluorescence was observed not only with the emission at 680 nm but also with F710, indicating that F710 is emitted by PSII Chl a. Development of F710 under red light was sensitive to cycloheximide, indicating that the development of the energy flow to F710 requires protein synthesis and that the emitter is installed in a protein encoded in the nuclear genome like the light-harvesting complex (LHC). Centrifugal fractionation of pigment-protein complexes revealed F710 to be located at fractions slightly heavier than the major LHC. Development of F 710 was also found in red-light-grown cells of the diatom Nitzschia closterium.