CHLOROPLAST MOVEMENT IN MOUGEOTIA INDUCED BY LONG AND SHORT-TERM DICHROMATIC IRRADIATION

Dichromatic irradiation of Mougeotia cells with high fluence rate of monochromatic light at 710 nm (far-red light, FR, unpolarized) and 620 nm (monochromatic light, OL, linearly polarized with electrical vector vibrating parallel to the cell axis) reoriented the chloroplasts from profile to face position. FR and OL applied separately had no effect on chloroplast movement. Chloroplast movement could be obtained: (a) during continuous dichromatic irradiation, (b) if FR was given as a background irradiation and OL as pulses, (c) if OL was given as a background irradiation and FR as pulses or (d) FR and OL pulses were applied simultaneously. The full extent of chloroplast response during pulse experiments dependend on: (a) intervals between successive pulses, (b) consecutive application of the pulses during about 30 min and (c) the fluence rate of pulses. Results obtained with long-term (1 min) or verv short-term (7 ns) duration of pulses were similar. In experiments with the application of the pulses the chloroplast movement depends to a greater degree on far-red light than 620 nm monochromatic light. This effect was manifested by the fact that for attaining a full expression the intervals between the successive pulses of far-red light had to be shorter than in the case of 620 nm light. The obtained results are interpreted as the possibility of P(fr) gradient formation between front and rear and at flanks of the cell. Moreover, we suggest that chloroplast movement induced by low fluence rate of red light and by high fluence rate of dichromatic irradiation (FR + OL) might start a different reaction chain leading to the same response.