Scalco Eleonora, Stec Krzysztof, Iudicone Daniele, Ferrante Maria Immacolata, Montresor Marina
Stazione Zoologica Anton Dohrn, Villa Comunale, Naples, 80121, Italy.
J Phycol. 2014 Oct;50(5):817-28. doi: 10.1111/jpy.12225. Epub 2014 Sep 14.
Sexual reproduction represents a fundamental phase in the life cycle of diatoms, linked to both the production of genotypic diversity and the formation of large-sized initial cells. Only cells below a certain size threshold can be sexualized, but various environmental factors can modulate the success of sexual reproduction. We investigated the role of cell density and physiological conditions of parental strains in affecting the success and timing of sexual reproduction in the marine heterothallic diatom Pseudo-nitzschia multistriata. We also studied the dynamics of the sexual phase in still conditions allowing cell sedimentation and in gently mixed conditions that keep cells in suspension. Our results showed that successful sexual reproduction can only be achieved when crossing parental strains in the exponential growth phase. Evidence was provided for the fact that sexual reproduction is a density-dependent event and requires a threshold cell concentration to start, although this might vary considerably amongst strains. Moreover, the onset of the sexual phase was coupled to a marked reduction in growth of the vegetative parental cells. The crosses carried out in physically mixed conditions produced a significantly reduced number of sexual stages as compared to crosses in still conditions, showing that mixing impairs sexualization. The results of our experiments suggest that the signaling that triggers the sexual phase is favored when cells can accumulate, reducing the distance between them and facilitating contacts and/or the perception of chemical cues. Information on the progression of the sexual phase in laboratory conditions help understanding the conditions at which sex occurs in the natural environment.
有性生殖是硅藻生命周期中的一个基本阶段，与基因型多样性的产生以及大型初始细胞的形成都有关联。只有低于一定大小阈值的细胞才能进行有性生殖，但各种环境因素可以调节有性生殖的成功率。我们研究了亲本菌株的细胞密度和生理条件对海洋异宗配合硅藻多列拟菱形藻有性生殖的成功率和时间的影响。我们还研究了在允许细胞沉降的静止条件下以及在使细胞保持悬浮的轻度混合条件下有性阶段的动态变化。我们的结果表明，只有在指数生长期将亲本菌株杂交时才能成功进行有性生殖。有证据表明，有性生殖是一个密度依赖性事件，开始需要一个阈值细胞浓度，尽管不同菌株之间可能有很大差异。此外，有性阶段的开始与营养亲本细胞生长的显著减少相关联。与在静止条件下的杂交相比，在物理混合条件下进行的杂交产生的有性阶段数量显著减少，表明混合会损害有性生殖。我们的实验结果表明，当细胞能够聚集时，触发有性阶段的信号传导更受青睐，这减少了细胞之间的距离，便于接触和/或感知化学信号。关于实验室条件下有性阶段进展的信息有助于理解自然环境中有性生殖发生的条件。
