英国广播公司（BBC）网站5日报导，加拿大研究人员发现一种既独特又怪异的植物寄生于动物体内的实例─绿藻入侵还在发育中的两栖动物蝾螈的胚胎与之共生，据研判其原因可能来自遗传。这项研究成果已刊载于美国国家科学院院刊 PNAS 。

首度证明植物与脊椎动物共生

这是首度有证据证明植物与脊椎动物共生。更奇怪的是，研究人员认为，这种北美地区常见的星点蝾螈，胚胎里之所以会有绿藻，可能是蝾螈胚胎遗传自它的父母。星点蝾螈只有在猎食与繁衍后代时才会浮出水面；它们在池塘里产卵，让卵在靠近水面处漂浮─对藻类而言，此处正是充满阳光又受到保护的理想环境。

主持这项研究计划的加拿大戴尔豪斯大学博士后研究员柯尼说，这些星点蝾螈的卵是绿色的，因为卵囊里有绿藻；卵囊里的绿藻为蝾螈胚胎提供氧气，绿藻也从胚胎排泄物取得所需要的氮。

此前，许多科学家认为，植物应该无法生长于脊椎动物的细胞内，因为鱼、鸟、爬虫类与哺乳动物（包括人类）等的脊椎动物，拥有相当特殊的免疫系统，应该不可能让外来有机体存活于其细胞内。

胚胎内绿藻 遗传自父母？

科学家早在一世纪前便已发现这种共生关系，但始终搞不懂绿藻如何进入胚胎内。柯尼说，他们在成年蝾螈的生殖器官内发现藻类的DNA，意味蝾螈胚胎内的绿藻，可能是遗传自它的父母，「我们称之为垂直传递（vertical transmission），但也有可能是垂直传递，再加上从环境中吸收藻类所致。

原文出处：

PNAS  doi: 10.1073/pnas.1018259108

Intracellular invasion of green algae in a salamander host

Ryan Kerneya,1, Eunsoo Kimb, Roger P. Hangarterc, Aaron A. Heissa, Cory D. Bishopd, and Brian K. Halla

The association between embryos of the spotted salamander (Ambystoma maculatum) and green algae (“Oophila amblystomatis” Lamber ex Printz) has been considered an ectosymbiotic mutualism. We show here, however, that this symbiosis is more intimate than previously reported. A combination of imaging and algal 18S rDNA amplification reveals algal invasion of embryonic salamander tissues and cells during development. Algal cells are detectable from embryonic and larval Stages 26–44 through chlorophyll autofluorescence and algal 18S rDNA amplification. Algal cell ultrastructure indicates both degradation and putative encystment during the process of tissue and cellular invasion. Fewer algal cells were detected in later-stage larvae through FISH, suggesting that the decline in autofluorescent cells is primarily due to algal cell death within the host. However, early embryonic egg capsules also contained encysted algal cells on the inner capsule wall, and algal 18S rDNA was amplified from adult reproductive tracts, consistent with oviductal transmission of algae from one salamander generation to the next. The invasion of algae into salamander host tissues and cells represents a unique association between a vertebrate and a eukaryotic alga, with implications for research into cell–cell recognition, possible exchange of metabolites or DNA, and potential congruence between host and symbiont population structures.