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 phototropiam In the rhizoida of B. hypnoides were investigated and analyzed in terms of bending. Both thaiii and rhlzoids developed from thallus segments exhibited typical tip growth, and their photoreceptive sites for phototroplam 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 Ca^2＋ had no effect on the bending curvature of thalli and rhlzolda. 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 microfilamenta.
Nai-Hao YeHong-Xia WangGuang-Ce WangZheng-Quan GaoDe-Mao Li
Bryopsis hypnoides Lamouroux was regenerated In vitro from the protoplasm squeezed out from wild algae and the regenerated Individuals had an advantage over Indlvlduala from the wild In terms of growth. Culturing of segments of thalll also showed that segments from the regenerated algae grew better than those from individuals from the wild. The segment that corresponds to a part of a cell, at least a part of the protoplasm, can develop Into a mature Individual, Including rhlzold and thallus, suggesting that a multlnucleate alga, such as B. hypnoides, Is different from higher plants, whose totlpotancy Is based on an Intact cell （or protoplasm）. Further cultivation of mature Individuals from segments Indicated that the organelles In the thallus had two ways In which they could survive when the alga was on the decline： （Ⅰ） the organelles were transferred Into a ball with a gelatinous envelope through a formed pipe and the ball seemed to be capable of being propagated; and （Ⅱ） the organelles were aggregated In the thallus and then moved to the outside. An Interesting result Is that one organelle aggregation located outside the thallus germinated and developed Into a mature alga, although most organelle aggregations gradually lost vitality and died. The results of the present study reveal that the aggregation of organelles can regenerate a stronger organism than Individuals from the wild owing to the complete exchange of genetic material and may possibly enable organelles to survive in unfavorable surroundings.
