Impact of UVR on vertical movement and photosynthetic efficiency of Euglena gracilis Klebs

PETER RICHTER,; P HADER, DONAT; VIRGINIA ESTELA VILLAFAÑE; WALTER HELBLING, E

Puerto Rico

Congreso; 33rd Annual Meeting of the American Society for Photobiology; 2006

Movement behavior and photosynthetic efficiency of the unicellular flagellate Euglena gracilis Klebswas investigated in vertical Plexiglas columns (depth = 65 cm, diameter = 15 cm). The columnscontaining the organisms were irradiated from above with a solar simulator (H nle lamp) receivingirradiances of 162, 32.6 and 1.08 W m-2 for PAR (400-700 nm), UV-A (315-400 nm) and UV-B(280-315 nm). Two treatments were implemented: One column was covered with a 295 nm cut-offfilter (thus receiving UVR- 280-400 nm, and PAR), and the other with a 395 nm cut-off filter (thusreceiving only PAR). Cell samples were drawn from different depths (ie., surface, 20, 40 and 65 cm)from which movement parameters were measured by image analysis, and photosynthetic efficiencydetermined with a pulse amplitude modulated fluorometer (Water PAM, Walz). UVR had significanteffect on both photosynthesis and swimming behavior. Photosynthetic efficiency increased with depthand samples exposed to UVR had a significant decrease in photosynthetic yield as compared thoseexposed only to PAR. Cells at the surface showed a negative gravitactic behavior (i.e., swimmingupward) whereas the fraction of cells swimming downward increased with depth below 20 cm. At 40cm depth about 50 % of the cells swam upward and 50 % downward whereas at 65 cm depth > 70% of the cells showed a downward movement. This resulted in that the largest fraction of cells was atthe bottom (i.e., 65 cm), while the number of cells towards the surface decreased. This situationreversed under low irradiance or dim light conditions, as more cells were found near the surface. Ourdata indicate that gravitaxis and thus the depth distribution of E. gracilis clearly depends on theradiation exposure.