Kataoka Hironao
Botanical Gardens, Tohoku University, Sendai, Japan.
Methods Mol Biol. 2019;1924:83-120. doi: 10.1007/978-1-4939-9015-3_8.
The coenocytic tip-growing alga Vaucheria exhibits positive and negative phototropism, apical expansion, polarotropism, and branch induction from the illuminated region of the cell, all of which are caused by blue light. The bending response of Vaucheria is a blue light-mediated growth response. Differently from diffuse-growing cells or organs, the apical hemispherical dome of the Vaucheria cell is the site of not only maximum growth activity but also the site of blue light perception. Thence the phototropic response is initiated by the bulging mechanism: that is, a quick shift of the growth center to the adjacent subapical flank region. Since tip growth is driven by localized exocytosis, both phototropic bending and branch induction are considered to be closely related blue light-responses. Here I describe first how to prepare a highly useful culture medium for most freshwater algae, to establish unialgal and axenic culture of Vaucheria, and then describe several simple illumination systems using ordinary and/or inverted microscopes for the measurements of tip growth and for analyses of phototropism, polarotropism, and blue light-induced branching. Brief information is also included concerning the nature and function of aureochrome, the newly discovered, ochrophyte-specific blue light receptor. Aureochrome mediates blue light-induced branching, but its role in the phototropic response is still not elucidated.
多核顶端生长的藻类毛霉藻表现出正向光性和负向光性、顶端扩展、极向性以及从细胞受光区域诱导分支，所有这些都是由蓝光引起的。毛霉藻的弯曲反应是一种蓝光介导的生长反应。与扩散生长的细胞或器官不同，毛霉藻细胞的顶端半球形圆顶不仅是最大生长活性的部位，也是蓝光感知的部位。因此，向光性反应是由凸起机制引发的：也就是说，生长中心快速转移到相邻的亚顶端侧翼区域。由于顶端生长是由局部胞吐作用驱动的，向光弯曲和分支诱导都被认为是密切相关的蓝光反应。在这里，我首先描述如何为大多数淡水藻类制备一种非常有用的培养基，建立毛霉藻的单种和无菌培养，然后描述几种使用普通和/或倒置显微镜的简单光照系统，用于测量顶端生长以及分析向光性、极向性和蓝光诱导的分支。还包括关于新发现的、褐藻门特有的蓝光受体金藻素的性质和功能的简要信息。金藻素介导蓝光诱导的分支，但其在向光反应中的作用仍未阐明。
