Orientation of pea chloroplast in an ac electric field

The orientation of pea chloroplast in an ac electric field was studied. The maximum linear dichroism signal at 681 nm was used as an indicator of orientation. It was found that the degrees of orientation depended on the frequency of the electric field. In the frequency range studied, there were two distinct dispersions at about 80 Hz and 750 kHz (α and β dispersion), and a maximum at about 100 kHz. The dependence of orientation on the electric field strength was used to estimate the polarizability. In agreement with the dispersion spectrum, there were stepwise decreases in polarizability at the two dispersions and an increase when moved into the region of the maximum. There was not permanent dipole detected.At a frequency below the α dispersion, an induced dipole arising from the oscillation of a counterion cloud, which is formed adjacent to the thylakoid membrane surface due to the presence of fixed surface charges, is believed to be a major cause of orientation. After the relaxation of this oscillation at higher frequency, the charge accumulation on both the inner and outer surfaces of the thylakoid membrane is believed to play a determinant role. Since the two interfacial polarizations have different dispersion frequencies, the polarizability of chloroplast increases after one dispersion (the maximum), which is then followed by a decrease at the second dispersion (the β dispersion).