Chepurnov Victor A, Mann David G, Sabbe Koen, Vyverman Wim
Laboratory of Protistology and Aquatic Ecology, Department of Biology, Ghent University, B-9000 Ghent, Belgium.
Int Rev Cytol. 2004;237:91-154. doi: 10.1016/S0074-7696(04)37003-8.
The diatoms are the most speciose group of algae, having global ecological significance in the carbon and silicon cycles. They are almost unique among algae in being diplontic, and sexual reproduction is an obligate stage in the life cycle of most diatom species. It is unclear which are the principal factors that have fostered the evolutionary success of diatoms, but the unique life cycle (which is correlated with a curious wall structure and cell division mechanism) and size-dependent control of sexuality must have played an important part. Progress in understanding life cycle dynamics and their interrelationships with population biology and evolution will depend on how successfully sex can be initiated and manipulated experimentally, and our review provides a foundation for such work. Relevant data are scattered in time and come mostly from non-English publications, producing a false impression of diatoms as recalcitrant with respect to sexualization. Recent advances dependent on experimental cultures include the discovery of widespread heterothallism (including some complex types of behavior) in pennate diatoms, sexual diversity among clones of centric diatoms, more flexible size restitution strategies in centric diatoms than had been suspected, and use of reproductive isolation as a criterion in diatom taxonomy. We identify unsolved problems in the life history of diatoms, including aspects of sexualization, cell-cell recognition, sexual reproduction, and the development of the special expanding cell (the auxospore), which is crucial to morphogenesis in this group. Some of these problems are being addressed using modern molecular genetic tools, and progress will be facilitated when whole-genome sequences are published (e.g., for Thalassiosira pseudonana). Problems of culture maintenance and methods for manipulating the life cycle are discussed.
硅藻是藻类中种类最为丰富的类群，在全球碳循环和硅循环中具有重要的生态意义。它们在藻类中几乎是独一无二的二倍体生物，有性生殖是大多数硅藻物种生命周期中的一个必要阶段。目前尚不清楚是哪些主要因素促成了硅藻在进化上的成功，但独特的生命周期（这与奇特的细胞壁结构和细胞分裂机制相关）以及与大小相关的性别控制肯定起到了重要作用。了解生命周期动态及其与种群生物学和进化之间的相互关系，将取决于能否在实验中成功诱导和操控有性生殖，而我们的综述为这类研究奠定了基础。相关数据分散在不同时期，且大多来自非英文出版物，这给人一种硅藻难以实现有性生殖的错误印象。基于实验培养的最新进展包括在羽纹硅藻中发现广泛存在的异宗配合现象（包括一些复杂的行为类型）、中心硅藻克隆间的性别多样性、中心硅藻比之前认为的更为灵活的大小恢复策略，以及将生殖隔离用作硅藻分类学的一个标准。我们指出了硅藻生活史中尚未解决的问题，包括有性生殖过程、细胞间识别、有性繁殖以及特殊的膨大细胞（复大孢子）的发育，复大孢子对于该类群的形态发生至关重要。其中一些问题正借助现代分子遗传学工具加以解决，当全基因组序列公布时（如拟南芥舟形藻），研究进展将得到推动。文中还讨论了培养维持的问题以及操控生命周期的方法。
