0000000000082366
AUTHOR
Heiko Mewes
Multiple Short Term Effects of UV-B Radiation on the Diatom Phaeodactylum Tricornutum
Increases in UV-B irradiance lead to many specific damaging effects upon the plants including damage of the thylakoid membrane, partial inhibition of PS II, decrease of chloroplast ATPase activity, loss of enzyme activities in the calvin cycle and alterations in pigment synthesis (1). Under natural conditions enhanced UV-B light is always accompanied by high intensities of photosynthetic active radiation (PAR). Damaging effects due to photoinhibitory PAR and UV-B light which lead to several oxygen radical species (2) could be reduced by photoprotection mechanisms. One of these protection mechanisms is the xanthophyll cycle. In higher plants and green algae violaxanthin is converted to zeaxa…
Supplementary Ultraviolet-B Radiation Induces a Rapid Reversal of the Diadinoxanthin Cycle in the Strong Light-Exposed DiatomPhaeodactylum tricornutum
AbstractA treatment of the diatom Phaeodactylum tricornutum with high light (HL) in the visible range led to the conversion of diadinoxanthin (Dd) to diatoxanthin (Dt). In a following treatment with HL plus supplementary ultraviolet (UV)-B, the Dt was rapidly epoxidized to Dd. Photosynthesis of the cells was inhibited under HL + UV-B. This is accounted for by direct damage by UV-B and damage because of the UV-B-induced reversal of the Dd cycle and the associated loss of photoprotection. The reversal of the Dd cycle by UV-B was faster in the presence of dithiothreitol, an inhibitor of the Dd de-epoxidase. Our results imply that the reversal of the Dd cycle by HL + UV-B was caused by an incre…