STUDENT ABSTRACTS - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 274

Mycosporine-like amino acids (MAAs) protect against UV-B-induced damage in
Gyrodinium dorsum
P.R. RICHTER, M. KLISCH, R. P. SINHA, D.-P. HÄDER
Friedrich-Alexander-Universität, Institut für Botanik und Pharmazeutische Biologie,
Erlangen, Germany
Gyrodinium dorsum is a marine motile dinoflagellate which is adapted to high
light conditions. In response to UV radiation the cells produce mycosporine-like amino
acids (MAAs), which show a strong absorbance in the UV range 1-2 . Experimental
evidence for their protective role against UV is still scarce. In the present study the
effect of an increased MAA content against excessive UV-B irradiation was tested.
The cells were grown in artificial seawater in a Kniese apparatus. In order to
stimulate the synthesis of MAAs in the cells the organisms were irradiated with artificial
solar radiation with 320 nm (UV-A + PAR) or 395 nm (PAR only) cut-off filters,
respectively, for a period of up to 48 h. Two cultures (with high MAA and low MAA
content, respectively) were exposed to high UV-B irradiation from a transilluminator or
solar radiation. The motility and velocity of the cells were analyzed at regular time
intervals.
The cells, which received UV-A during the induction synthesized large amounts
of MAAs, while the cells which were exposed to PAR only showed a marginal increase
in their MAA content. Five MAAs, shinorine (334 nm), porphyra-334 (334 nm),
palythine (320 nm) and two unidentified MAAs having O max at 310 and 331 nm,
respectively, were detected by HPLC analyses. Cells, which were pretreated with UV-A
and PAR were considerably more resistant against high artificial UV-B radiation, as can
be seen from the kinetics of motility and velocity. While the cells with low MAAs
content showed a complete loss of motility within 3 h, the cells with high MAAs
content survived at least 2 times longer. Also the decrease in velocity was much faster
in the induced cells. A protective effect of MAAs was also detected against solar
radiation. Induced and not-induced cells (same treatment as in the previous experiment,
MAA synthesis was similar) were exposed to solar radiation. While cells which were
pretreated with UV and PAR were not affected by solar radiation, the not-induced (PAR
only) cells lost their motility completely within about 150 min. The experiments were
repeated several times with consistently the same results.
The data from these experiments are in good agreement with a detected
screening effect of MAAs against inhibition of photosynthesis in the dinoflagellate G.
sanguineum 4 . The results indicate that MAAs function as UV absorbing/screening
compounds in Gyrodinium dorsum and help the cells to survive in a high UV radiation
regime.
References
1. Klisch M, Häder D-P (2000) Mycosporine-like amino acids in the marine dinoflagellate Gyrodinium
dorsum : induction by ultraviolet irradiation, J Photochem Photobiol B.: Biol 55: 178-182.
2. Sinha RP, Klisch M, Gröniger A, Häder D-P (1998) Ultraviolet-absorbing/screening substances in
cyanobacteria, phytoplankton and macroalgae, J Photochem Photobiol B: Biol 47: 83-94.
3. Klisch M, Sinha RP, Richter PR, Häder D-P (2001) Mycosporine-like amino acids (MAAs) protect against
UV-B-induced damage in Gyrodinium dorsum Kofoid, J Plant Physiol 158: 1449-1454.
4. Neale PJ, Banaszak AT, Jarriel CR (1998) Ultraviolet sunscreens in Gymnodinium sanguineum
(Dinophyceae): mycosporine-like amino acids protect against the inhibition of photosynthesis, J Phycol 34:
928-938.