Using high-speed microcinematography (1OO-5OO f/s) the movement of Chlamydomonas reinhardtii mutant 622 E has been studied with frame-by-frame analysis. The stigma lies in the cell equator, displaced out of the flagellar plane anticlockwise by an angle of about 45". During forward movement the cells rotate anticlockwise about their long axis with a frequency of 1.4-2 Hz (maximum 2.5 Hz). The rotation is caused by a lateral component of 3-dimensional beating of the flagella during the effective strokes. The helical swimming path is a result of an unequal flagellar beating. This is normally synchronous, but synchrony is interrupted from time to time by an additional beat of the outward directed flagellum, in our study one after about every twenty beats on average. These results are discussed and compared with the results published by other groups.

No abstract

Photoinhibition of photosynthesis and its recovery was investigated in the laboratory and in the field with fluorescence and oxygen measuring devices. Photosynthetic efficiency measured at non-saturating fluence rates and the ratio of variable fluorescence to maximal fluorescence (FJF,) showed an approximately inverse course compared to the fluence rate of daylight measured continuously during the day. In the morning photosynthetic efficiency was high, but decreased with increasing fluence rate. Maximal photoinhibition of photosynthesis occurred around noon or in the early afternoon. During the afternoon photosynthetic efficiency increased again and full recovery was reached in the evening. These lunetics of recovery differ from those obtained in the laboratory under artificial conditions, where the red algae required up to 48 h to recover from a strong photoinhibition. Different species showed Mferent sensitivity to photoinhibition and different capability for recovery. The red alga Porphyra spp., living in the upper eulittoral, was able to cope with the high fluence rates at the water surface. The red alga Delesseria sanguinea, living in the subtidal zone, shows the highest sensitivity to photoinhibition. Thus, a relation between photoinhibitory sensitivity and the zonation of the algae in the littoral exists.

In response to step-up as well as step-down blue or white light stimuli, changes of beat pattern were observed in the two flagella of Chlamydomonas. The front amplitude was either increased or decreased, always in reverse in the two flagella. Again, two opposite combinations of step-up and step-down responses were found roughly in parallel to the two types of beat frequency changes. It is shown that positive phototaxis is probably achieved by the first type [called type (+)I and negative phototaxis by the second one [called type (-)I. Comparative measurements have revealed that frequency is not only related to the rate of flagellar movement, but also to the beat pattern. The rate of movement may change in different ways in the recovery and in the effective stroke. Though beat frequency and pattern changes are opposite in the two types, the rates of movement of the two flagella during the effective stroke are not always. In type (-) divergent changes were found in the rates of effective stroke movement, perhaps indicating the involvement of an additional mechanism.