Blue-fluorescence of NADPH as an indicator of marine primary production

Abstract

Nicotinamide Adenine Dinucleotide Phosphate (NADPH) is the primary product of photosynthesis
and can therefore serve as an indicator of biomass and photosynthetic activity. Pure NADPH which
is the reduced form of NADP shows an absorption maximum at 340 nm and a maximum of emission
at 460 nm. NADPH concentrations in terrestrial vegetation have already been studied since
1957 in great detail with optical methods. However, its potential as a biomass parameter of oceanic
phytoplankton which can be assessed in situ and remotely with fluorescence spectroscopy has not
yet been investigated.
In this paper, we report on laboratory investigations of the blue-fluorescence spectrum in algal
suspensions of Chlorella and Thalassiosira when excited with UV-A light. It is shown that cell densities
of about 106 per litre as they are typically found under natural conditions are too low for precise
detection of NADPH fluorescence, while concentrated samples with 108-1010 cells per litre exhibit
significant blue-fluorescence which can be related to NADPH. Inhibition of photosynthetic activity
by addition of DCMU decreases the strength of blue-fluorescence remarkably. Since NADPH
is an end product of photosynthesis, changes of PAR illumination levels should directly affect its
concentration and hence the intensity of blue-fluorescence. However, no effect of illumination on
blue-fluorescence could be observed in our study. Possible reasons of these observations are discussed,
and perspectives for practical applications of the method used are proposed.

More information

Identifiers

Catalogue record

Export record