De Vega Clara, Ortiz Pedro Luis, Arista Montserrat, Talavera Salvador
Departamento de Biología Vegetal y Ecología, Facultad de Biología, Universidad de Sevilla, Apdo-1095, 41080 Sevilla, Spain.
Ann Bot. 2007 Dec;100(6):1209-17. doi: 10.1093/aob/mcm217. Epub 2007 Sep 5.
One of the most extreme manifestations of parasitism is found in the genus Cytinus, a holoparasite whose vegetative body is reduced to an endophytic system living within its host root. There are two species of Cytinus in the Mediterranean, C. hypocistis and C. ruber, which parasitize various genera of Cistaceae, one of the most characteristic families of the Mediterranean scrublands. The aim of this work is to describe the endophytic systems of C. hypocistis and C. ruber, and their tissue relationships with their host.
Roots from five different hosts infected with C. hypocistis and C. ruber were harvested, and examined by anatomical techniques under light microscopy to elucidate the characteristics of the endophytic system of Cytinus, and to determine if differences in endophytic systems occur between the two species and in response to different hosts.
The endophyte structure is similar in both Cytinus species irrespective of the host species. In the initial stages of the endophyte, rows of parenchymal cells spread through the host pericyclic derivatives and phloem, and begin to generate small nodules in the outermost region of the host xylem. Later the nodules anastomose, and bands of parasitic tissue are formed. The host cambium continues to develop xylem tissue, and consequently the endophyte becomes enclosed within the xylem. The bands of parasitic tissue fuse to form a continuous sheath. This mature endophyte has well-developed vascular system with xylem and phloem, and forms sinkers with transfer cells that grow through the host xylem.
The endophytic system of Cytinus develops in all host root tissues and reaches its most mature stages in the host xylem. It is more complex than previously reported, showing parenchyma, xylem and phloem tissues. This is the first report of well-developed phloem in a holoparasitic endophytic species.
寄生现象最极端的表现之一见于 Cytinus 属，该属为全寄生植物，其营养体退化为寄生于宿主根部的内生系统。地中海地区有两种 Cytinus，即 C. hypocistis 和 C. ruber，它们寄生于半日花科的多个属，半日花科是地中海灌木丛最具代表性的科之一。本研究旨在描述 C. hypocistis 和 C. ruber 的内生系统，以及它们与宿主的组织关系。
采集了感染 C. hypocistis 和 C. ruber 的五种不同宿主的根，通过光学显微镜下的解剖技术进行检查，以阐明 Cytinus 内生系统的特征，并确定这两个物种之间以及对不同宿主的内生系统是否存在差异。
无论宿主物种如何，两种 Cytinus 物种的内生结构相似。在内生系统的初始阶段，成排的薄壁细胞穿过宿主的中柱鞘衍生物和韧皮部，并开始在宿主木质部的最外层区域形成小结节。随后小结节相互吻合，形成寄生组织带。宿主形成层继续发育木质部组织，因此内生体被包裹在木质部内。寄生组织带融合形成连续的鞘。这种成熟的内生体具有发育良好的维管系统，包括木质部和韧皮部，并形成具传递细胞的吸器，穿过宿主木质部生长。
Cytinus 的内生系统在所有宿主根组织中发育，并在宿主木质部中达到最成熟阶段。它比以前报道的更为复杂，显示出薄壁组织、木质部和韧皮部组织。这是首次报道全寄生内生物种中发育良好的韧皮部。
