Mouget Jean-Luc, Gastineau Romain, Davidovich Olga, Gaudin Pierre, Davidovich Nickolai A
Laboratoire de Physiologie, Université du Maine, Le Mans, France.
FEMS Microbiol Ecol. 2009 Aug;69(2):194-201. doi: 10.1111/j.1574-6941.2009.00700.x. Epub 2009 May 6.
Sexual reproduction is an obligatory phase in the life cycle of most diatoms, as cell size decreases with successive vegetative divisions and the maximal cell size is only restored by a specialized cell, the auxospore, which follows zygote formation as a result of sexual reproduction. While in pennate diatoms the induction of sexual reproduction depends primarily on cell-cell interactions, the importance of different external factors for the induction of sexual reproduction is less well known. Here, we investigated the effects of light on sexualization in the marine benthic pennate diatom Haslea ostrearia (Gaillon) R. Simonsen. Compatible clones were crossed and exposed to different combinations of light levels, qualities, and photoperiods. Light was found to be a key factor for sexualization, and to a certain extent, to control auxosporulation in H. ostrearia. The light conditions most favorable for sexual reproduction were low irradiances (<50 micromolphotons m(-2) s(-1)) and short photoperiods (6-10 h), conditions that prevail during winter, and to a lesser extent, the higher irradiances and longer photoperiods that correspond to the spring and fall, when blooms of this organism form in the natural environment. Auxospore formation was very rare in continuous light, and maximum in presence of red radiation, while it was never observed in darkness or in radiation other than red.
有性生殖是大多数硅藻生命周期中的一个必经阶段，因为细胞大小会随着连续的营养分裂而减小，而最大细胞大小只有通过一种特殊的细胞——复大孢子才能恢复，复大孢子是有性生殖后合子形成的结果。在羽纹硅藻中，有性生殖的诱导主要取决于细胞间的相互作用，而不同外部因素对有性生殖诱导的重要性则鲜为人知。在这里，我们研究了光照对海洋底栖羽纹硅藻哈氏骨条藻（Haslea ostrearia (Gaillon) R. Simonsen）有性生殖的影响。将兼容的克隆进行杂交，并使其暴露于不同的光照强度、光质和光周期组合下。结果发现，光照是有性生殖的关键因素，并且在一定程度上控制了哈氏骨条藻的复大孢子形成。最有利于有性生殖的光照条件是低辐照度（<50微摩尔光子·米-2·秒-1）和短光周期（6 - 10小时），这些条件在冬季较为常见，在一定程度上也对应于春季和秋季较高的辐照度和较长光周期，此时该生物在自然环境中会形成水华。在连续光照下复大孢子形成非常罕见，在红光照射下最多，而在黑暗或除红光以外的其他辐射下从未观察到复大孢子形成。
