EFFECTS OF UV-B IRRADIATION ON PHOTOMOVEMENT IN THE DESMID, Cosmarium cucumis

Sensitivity of photosynthesis to UV radiation in several Cosmarium strains (Zygnematophyceae, Streptophyta) is related to their geographical distribution

The application of UV radiation in vitro on desmid strains collected from various climatic areas and long-term grown under identical laboratory conditions revealed their preference for specific climatic niches, as judged from their different photosynthetic behaviours.

Orientation of the photosynthetic flagellate, Peridinium gatunense, in hypergravity

The photosynthetic freshwater flagellate, Peridinium gatunense, uses both positive phototaxis and negative gravitaxis to move upwards in the water column. At higher fluence rates approaching those at the surface of their habitat, the cells tend to become unoriented and thus stop their upward movement. Orientation and motility of Peridinium gatunense has been studied in the slow rotating centrifuge microscope (NIZEMI), which allows observation of swimming behavior during centrifugation acceleration between 1 g and 5g. The movement vectors were analyzed by real time image analysis capable of tracking many cells simultaneously. At 1 g the orientation was not very precise, but the degree of orientation increased significantly at higher acceleration forces up to about 3 g. Most cells were capable of swimming even against an acceleration vector of 3.8 g; at higher acceleration forces the cells were not able to cope with the centrifugal force. The linear velocity of cells swimming against 1 g was about 20% lower than that of cells moving in other directions. The velocity decreased even more in cells swimming against higher acceleration forces.

Motility and gravitactic orientation of the flagellate, Euglena gracilis, impaired by artificial and solar UV-B radiation

The effects of ultraviolet radiation on the gravitactic orientation of the freshwater flagellate, Euglena gracilis, were determined by a real time image analysis system. Both artificial UV radiation and solar radiation in a temperature-controlled growth chamber were employed. Histograms of gravitaxis showed that the degree of orientation decreased with increasing exposure time; this can be quantified using the Rayleigh test and upper quadrant summation. The effects of artificial UV radiation on the orientation are considerably stronger than those of solar radiation, probably because the radiation source emits higher fluence rates below 300 nm than found in solar radiation. The effects of monochromatic ultraviolet radiation on motility have been determined, and an action spectrum has been calculated.