Cellular organization in germ tube tips of Gigaspora and its phylogenetic implications
Cellular organization in germ tube tips of Gigaspora and its phylogenetic implications
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DOI：
10.3852/12-291
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发表时间：
2013-09-01
期刊：
影响因子：
2.8
通讯作者：
McLaughlin, David J.
中科院分区：
文献类型：
--
作者：
Bentivenga, Stephen P.;Kumar, T. K. Arun;McLaughlin, David J.
真菌菌丝尖端精细结构的比较形态通常可以提供系统发育信息。特别是，Spitzenkorper 的形态在高等分类群中有所不同。迄今为止，还没有人彻底表征球囊菌门成员的菌丝尖端，并将其与其他真菌进行比较。这部分是由于这些专性共生体的活菌丝生长和操作困难。我们结合光学显微镜 (LM) 和透射电子显微镜 (TEM) 观察了 Gigaspora gigantea、G. margarita 和 G. Rosea 的芽管生长。对于 TEM，我们使用传统的化学固定和冷冻固定方法。所有物种的生殖管对操纵都极其敏感。健康的胚芽管通常表现出快速的双向细胞质流动，而受到干扰的胚芽管则表现出细胞质运动减少或没有细胞质运动。活跃生长的芽管包含一簇 10-20 个球形体，位于顶点后面约 3-8 微米处。我们假设这些小体是脂质体，它们在健康的细菌管中快速移动。这些物体在任何细胞扰动后立即消失。与用传统化学方法处理的细胞相比，用冷冻技术制备的细胞具有更好的保存性。例如，冷冻制备的样品显示出两个细胞壁层，尖端附近至少有三种囊泡类型，并且注意到三个不同的细胞质区域。我们没有使用 LM 或 TEM 技术检测到 Spitzenkorper，并且 Gigaspora 芽管的尖端组织似乎与接合菌真菌中的菌丝相似。这一观察结果得到了对五个真菌门成员菌丝尖端微观特征的系统发育分析的支持。我们的工作强调细胞组织的敏感性，以及需要尽可能少的操作来准确观察胚管结构。
Comparative morphology of the fine structure of fungal hyphal tips often is phylogenetically informative. In particular, morphology of the Spitzenkorper varies among higher taxa. To date no one has thoroughly characterized the hyphal tips of members of the phylum Glomeromycota to compare them with other fungi. This is partly due to difficulty growing and manipulating living hyphae of these obligate symbionts. We observed growing germ tubes of Gigaspora gigantea, G. margarita and G. rosea with a combination of light microscopy (LM) and transmission electron microscopy (TEM). For TEM, we used both traditional chemical fixation and cryo-fixation methods. Germ tubes of all species were extremely sensitive to manipulation. Healthy germ tubes often showed rapid bidirectional cytoplasmic streaming, whereas germ tubes that had been disturbed showed reduced or no cytoplasmic movement. Actively growing germ tubes contain a cluster of 10-20 spherical bodies approximately 3-8 mu m behind the apex. The bodies, which we hypothesize are lipid bodies, move rapidly in healthy germ tubes. These bodies disappear immediately after any cellular perturbation. Cells prepared with cryo-techniques had superior preservation compared to those that had been processed with traditional chemical protocols. For example, cryo-prepared samples displayed two cell-wall layers, at least three vesicle types near the tip and three distinct cytoplasmic zones were noted. We did not detect a Spitzenkorper with either LM or TEM techniques and the tip organization of Gigaspora germ tubes appeared to be similar to hyphae in zygomycetous fungi. This observation was supported by a phylogenetic analysis of microscopic characters of hyphal tips from members of five fungal phyla. Our work emphasizes the sensitive nature of cellular organization, and the need for as little manipulation as possible to observe germ tube structure accurately.