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Transient Photoresponses of a Phototactic Microorganism, Haematococcus Pluvialis, Revealed by Light Scattering

By Franco Angelini, Cesare Ascoli, Carlo Frediani and Donatella Petracchi


A new method, using incoherent light scattering, has been developed to measure the flagellar beating frequency of swimming microorganisms. By means of this method, transient changes of flagellar beating frequency in response to white light flashes have been revealed in samples of a phototactic microorganism, Haematococcus pluvialis. An increase of flagellar beating frequency occurs when the flash dose (flash intensity × flash duration) is sufficient. Reciprocity between light intensity and flash duration holds for durations not exceeding 60-80 ms. For lower doses a bimodal distribution of flagellar beating frequency is revealed. No effect is observed for very low flashes or for red stimuli, whereas green light is effective. A detailed analysis of experimental results has allowed us to determine the characteristic time of the effect and follow its evolution. The correlation of this effect with visually observed behavior is discussed and a possible underlying mechanism is suggested

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OAI identifier: oai:pubmedcentral.nih.gov:1329818
Provided by: PubMed Central
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