INDUCTION OF CHLOROPLAST MOVEMENT IN THE ALGA Mougeotia BY POLARIZED NANOSECOND DYE‐LASER PULSES*^†

Abstract

Chloroplast movement of white‐light treated alga Mougeotia was induced by 15‐ns dye‐laser pulses (620‐690 nm). A single pulse, polarized perpendicular to the cell axis, does not induce a significant response, although full response can be obtained when the same fluence is applied during a 30‐s irradiation. However, for 620 and 660 nm perpendicularly polarized flash irradiation results in a significant response, if the total fluence is given by 2 consecutive flashes with 2‐s dark interval (double‐flash effect), and full response can be obtained by poly‐flash induction. Flashes of 690 nm in no case induce a response. Similar to the case of lettuce‐seed germination (Scheuerlein and Braslavsky, 1985), the establishment of a photochromic system between Pr and the very early intermediates (= lumi‐R) during the 15‐ns laser pulse can explain the results. At 690 nm, the photochromic system is shifted more extensively to Pr than at shorter wavelengths; thus, Pfr formation is strongly diminished. At shorter wavelengths (620 and 660 nm) the inhibition of Pfr formation by the existence of this photochromic system is smaller. The results are compatible with parallel dipole moments of the chromophores in Pr and in the first intermediates. A smaller but still significant response is obtained for repeated pulses of 660‐nm light, polarized parallel to the cell axis. These results are explained by a gradient in light sensitivity around the cell axis (induced by the white‐light pretreatment) and an increasing Plr concentration, established around the cell axis, as a function of the number of pulses.

INTERMEDIATES IN THE PHOTOCONVERSION OF FUNCTIONAL PHYTOCHROME IN FERN SPORES OF Dryopteris–II. In vivo KINETICS OF THE DECAY OF Ii700 AND OF THE FORMATION OF Pfr STUDIED WITH A DOUBLE‐LASER APPARATUS*

“…This is due to the photoreversion of I;oo to P,, thus diminishing the formation of Pfr from the intermediate I;(H,. Similar results were described for in vivo studies to polarotropism in fern protonemata (Kadota et al, 1986), seed germination of lettuce (Scheuerlein and Braslavsky , 1985), or chloroplast orientation in Mougeotia (Scheuerlein and Braslavsky, 1987).…”

Chloroplast movement

“…(1) Low-intensity movement can be induced by single pulses of red light as short as a millisecond (Haupt & Bretz, 1976;Scheuerlein, Walczak & Gabrys, 1987) or even below a microsecond (Scheuerlein & Braslavsky, 1987), continuing then in darkness. High-intensity movement, however, usually requires continuous irradiation during the whole response; upon a light pulse of a few minutes this movement stops very soon in darkness.…”