Chlamydomonas mutants missing the central pair or radial spokes are paralyzed despite the fact that they have the full wild-type complement of functional dynein ATPases. We show here that these mutants can move under conditions of low ATP concentration, a combination of ATP and ADP, and a combination of ATP and ribose-modified ATP analogs. These conditions suggest an inhibitory role of ATP and that this inhibition can be relieved by ADP or analogs. The function of the central-pair/radial spoke complex may be to release this ATP inhibition in a controlled manner.

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Label-free, non-invasive, rapid absorbance spectral imaging A(x,y,λ) microscopy of single live cells at 1.2 μm × 1.2 μm resolution with an NA = 0.85 objective was developed and applied to unicellular green algae Chlamydomonas reinhardtii. By introducing the fiber assembly to rearrange a two-dimensional image to the one-dimensional array to fit the slit of an imaging spectrograph equipped with a CCD detector, scan-free acquisition of three-dimensional information of A(x,y,λ) was realized. The space-resolved absorbance spectra of the eyespot, an orange organelle about 1 μm, were extracted from the green-color background in a chlorophyll-rich single live cell absorbance image. Characteristic absorbance change in the cell suspension after hydrogen photoproduction in C. reinhardtii was investigated to find a single 715-nm absorption peak was locally distributed within single cells. The formula to calculate the absorbance of cell suspensions from that of single cells was presented to obtain a quantitative, parameter-free agreement with the experiment. It is quantitatively shown that the average number of chlorophylls per cell is significantly underestimated when it is evaluated from the absorbance of the cell suspensions due to the package effect.

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