High-fluence rate responses in the light-oriented chloroplast movement in Adiantum protonemata

Abstract

Light-oriented chloroplast movement in the protonema of the fern Adiantum capillus-veneris L. was studied using the techniques of 2-h local and whole-cell irradiation. Local irradiation of protonemata with high-fluence rate blue light (BL) or red light (R) moved chloroplasts out of the irradiated area (negative response). Whole-cell irradiation with high-fluence rate BL accumulated chloroplasts at the flanks of cells (parastrophe). In the latter experiment, polarized light having the vibration plane perpendicular to the protonema axis was more effective than unpolarized light, and parallel polarized light was ineffective. All these responses were the reverse of those induced by low-fluence rate R and BL irradiation. A whole-cell irradiation with high-fluence rate R accumulated chloroplasts at the front and the rear of cells (diastrophe) in the same way as that with low-fluence rate R. It was also found that the high-fluence rate BL prevented R actions in chloroplast movement. That the photoceptors involved in these high-fluence rate responses were the same as those for the low-fluence rate responses, a BL photoreceptor for BL and phytochrome for R, was deduced from the effects of local and whole-cell irradiations with R and far-red light as well as from the action dichroism observed with the whole-cell irradiation. Possible mechanisms of the negative responses are discussed.