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The effects of the motility inhibitors 2,3-butanedione monoxime (BDM) and latranculin A (Lat A) on the motility, photosynthetic activity and pigment composition of the benthic diatoms Cylindrotheca closteriumand Pleurosigma angulatumwere studied. BDM inhibited diatom gliding, preventing motility at concentrations of 12.5 mM and 50 mM for C. closteriumand P. angulatum, respectively. For both species, the quantum yield of PSII (ΔF/Fm′) decreased with increasing concentrations of BDM. Reduced excitation at PSII reaction centres were caused by BDM-induced conversion of the pigment diadinoxanthin to diatoxanthin, through the activation of the xanthophyll cycle. Lat A inhibited diatom gliding, preventing motility at concentrations of 0.1 μM and 0.25 μM for C. closteriumand P. angulatum, respectively. Concentrations of Lat A as high as 1 μM showed no significant effects on the PSII quantum yield, on the light-response curves of relative electron transport rate (initial slope of light curve, a, and maximum relative electron transport rate, ETRm), or on the pigment composition of treated diatom cells. These results indicate that BDM has unavoidable effects on the photosynthetic activity by affecting the xanthophyll cycle, which hamper its use as a motility inhibitor in diatom studies. On the other hand, the absence of effects of Lat A on the photosynthetic activity makes this motility inhibitor a useful tool for the study of the ecological and photophysiological relevance of benthic diatom migration.

Letter to the Editor