Phototactic responses in the gametes of the brown alga, Ectocarpus siliculosus
Phototactic responses in the gametes of the brown alga, Ectocarpus siliculosus
复制标题
褐藻 Ectocarpus siliculusus 配子的趋光反应
作者：
H. Kawai;D. Müller;E. Fölster;D. Häder
使用计算机化的细胞跟踪系统确定了趋光性的作用谱，并研究了外果配子（外果目、褐藻纲）的光感受机制。对柱头的精细结构和鞭毛肿胀进行了分析，首次论证了柱头的反光功能。在单色光刺激下，外果配子在370 nm~520 nm之间主要表现出正趋光性。作用光谱在 380 nm 附近有一个小峰，在 430 nm 和 450 nm 或 460 nm 处有两个主峰，在 470 nm 处有一个肩部，毗邻 440 nm 附近的显着凹陷。在每秒超过四个脉冲的单侧频闪照明下，配子表现出明显的趋光性。然而，响应在较低频率下受到干扰。添加甲基纤维素会增加培养基的粘度并减慢配子旋转，从而降低阈值频率。这些结果表明配子的旋转在感光机制中起着重要作用。在 90° 角的等强度双边照明下，大多数配子在两束光束之间的合成物上游动。当两束光束的角度大到 120° 时，这种响应就会受到干扰。透射电子显微镜观察表明，鞭毛肿胀恰好与柱头中心区域叶绿体的凹陷相吻合。电子致密材料存在于远离柱头的鞭毛肿胀部分。没有屏障滤光片的落射荧光显微镜和落射偏振显微镜显示，柱头反射蓝光。提出了一个假设，讨论反射光聚焦到鞭毛肿胀上的可能性。
The action spectrum of phototaxis was determined and the photoreceptive mechanism was studied in Ectocarpus gametes (Ectocarpales, Phaeophyceae) using a computerized cell-tracking system. The fine structures of the stigma and the flagellar swelling were analyzed, and the reflective function of the stigma was demonstrated for the first time. Under monochromatic light stimulation, Ectocarpus gametes show mainly positive phototaxis between 370 nm and 520 nm. The action spectrum has a minor peak near 380 nm, and two major peaks at 430 nm and 450 nm or 460 nm and a shoulder at 470 nm adjoining a remarkable depression near 440 nm. Under unilateral stroboscopic illumination with more than four pulses per second, the gametes show clear phototaxis. However, the response is disturbed at lower frequencies. Addition of methyl cellulose, which increases the viscosity of the medium and slows down gamete rotation, decreases the threshold frequency. These results indicate that rotation of the gamete plays an essential role in the photoreceptive mechanism. Under equal intensities of bilateral illumination at an angle of 90°, most of the gametes swim on the resultant between the two light beams. This response is disturbed when the angle of the two light beams is as large as 120°. Observations by transmission electron microscopy show that the flagellar swelling fits precisely into a concave depression of the chloroplast at the central region of the stigma. Electron-dense material is present in that sector of the flagellar swelling which faces away from the stigma. Epifluorescence microscopy without a barrier filter and epipolarization microscopy reveal that stigmata reflect blue light. A hypothesis is formulated which discusses the possibility that the reflected light is focused onto the flagellar swelling.