Two components of photoreceptor potential in phototaxis of the flagellated green alga Haematococcus pluvialis

The kinetics of the photoreceptor potential of phototaxis in biflagellated green alga Haematococcus pluvialis in response to a 10-ns laser pulse of three wavelengths (465, 550, and 590 nm) were measured in single cells with 30 μs time resolution. The rise and the decay of photoinduced potential are both at least biphasic. The first component of the rise is very stable and has no measurable (<30 μs) time delay. The second component is triggered after a 120-400-μs lag period, depending on flash intensity. Its appearance is sensitive to the physiological state of the cell and the amplitude can be increased by phototactically ineffective red background illumination. The electrical generators for both components are localized in the same region of the cell membrane (on the stigma-bearing side) and these components have the same depolarizing sign. The results indicate that the photoreceptor potential in phototaxis comprises two components, which could be interpreted as light-induced charge movement within the photoreceptor molecules and changes in ion permeability of the cell membrane.     

Homochirality of Biomolecules: Counter-Arguments Against Critical Notes

Three recently published critical papersby Bonner and coworkers on the extraterrestrial origin of thehomochirality of biomolecules and the amplification of tinyenantiomeric excess are discussed. The presented arguments showthe difficulties involved in circularly polarized u.v. andvisible synchrotron radiation from neutron stars, in their ratioto non circularly polarized light and in racemization of theproducts. Attention is called upon another mechanism forproduction of extraterrestrial handedness based on Salam'scondensation theory and on the recent experimental demonstrationof the enantioselective magnetochiral photochemistry. Arguments,as well as experiments, point out that tiny enantiomeric excessesmight be amplified via the Yamagata accumulation principlequestioned by Bonner.