Phototropism of Thalli and Rhizoids Developed from the Thallus Segments of Bryopsis hypnoides Lamouroux |
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Authors: | Nai-Hao Ye Hong-Xia Wang Guang-Ce Wang Zheng-Quan Gao De-Mao Li |
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Affiliation: | (Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences;, Qingdao 266071, China;Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences;, Qingdao 266071, China;School of Life Sciences, Shandong University of Technology;, Zibo 255049, China) |
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Abstract: | Newly regenerated thalli were used to study the phototropism of Bryopsis hypnoides Lamouroux under different qualities of light. Positive phototropism in the thalli and negative phototropism in the rhizoids of B. hypnoides were investigated and analyzed in terms of bending. Both thalli and rhizoids developed from thallus segments exhibited typical tip growth, and their photoreceptive sites for phototropism were also restricted to the apical hemisphere. The bending curvature of rhizoids and thalli were determined with unilateral lights at various wavelengths and different fluence rates after a fixed duration of illumination. The trends of bending from the rhizoid and thallus were coincident, which showed that the action spectrum had a large range, from ultraviolet radiation (366.5 nm) to green light (524 nm). Based on the bending curvatures,blue light had the highest efficiency, while the efficiency of longer wavelengths (>500 nm) was significantly lower. External Ca2+ had no effect on the bending curvature of thalli and rhizoids. Blue light (440 nm) induced thallus branching from rhizoids, while red light (650 nm) had no such effect. Fast-occurring chloroplast accumulation in the outermost cytoplasmic layer of the blue light (440 nm)-irradiated region in the rhizoid was observed, from which protrusions (new thalli) arose after 4 h of the onset of illumination, and this action was thought to be driven by the dynamics of actin microfilaments. |
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Keywords: | Bryopsis hypnoides chloroplast accumulation phototropism rhizoid thallus |
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