PHYTOCHROME-MEDIATED RESPONSE IN MOUGEOTIA TO VERY SHORT LASER FLASHES

Chloroplast orientation to the light direction in the green alga Mougeotia could be induced with high efficiency by flashes of 100 ns duration and a wavelength of 694 nm if we started with phytochrome mainly in the Pfr form. With increasing fluences, however, an optimum was surpassed, and no response was found in the highest fluences. In addition, the well-known action dichroism disappeared near the optimum fluence and even may have been reversed. In contrast, after saturating FR, i.e. with phytochrome in the Pr form, no response could be induced, neither by single nor by repetitive laser flashes. These preliminary results do not as yet allow far-reaching conclusions. © 1979.