Single-cell chlorophyll fluorescence kinetic microscopy ofPylaiella littoralis(Phaeophyceae) infected byChytridium polysiphoniae(Chytridiomycota)

Chlorophyll fluorescence imaging is a non-invasive method to monitor the metabolic state of photosynthetic organisms. We used spatially resolved (imaging) microscopic measurements of chlorophyll fluorescence kinetics to follow the fate of individual cells of the filamentous brown alga Pylaiella littoralis infected by the biotrophic parasite Chytridium polysiphoniae (Chytridiomycota). These measurements showed strong differences between individual parameters of the inhibition of photosynthesis, revealing important details about the mechanism of damage. The dark-adapted photochemistry of photosystem II itself (measured as Fv/Fm, where Fv = Fm − F0) remained unaffected until a very late stage of damage to the cell, while the light-adapted efficiency of PSII electron transport decreased earlier. A particularly complex pattern was found for the changes in nonphotochemical quenching (NPQ). The shape of the fluorescence transients suggests that the changes in NPQ during the actinic light period are caused by cha...