Reynaga-Peña C G, Bartnicki-Garcia S
Department of Plant Pathology, University of California, Riverside, California 92521, USA.
Fungal Genet Biol. 1997 Dec;22(3):153-67. doi: 10.1006/fgbi.1997.1003.
An apical branching, temperature-sensitive, mutant of Aspergillus niger (ramosa-1) was isolated by UV mutagenesis. Ramosa-1 has a wild type morphology at 23 degrees C, but branches apically when shifted to 34 degrees C. The cytological events leading to apical branching were recorded by video-enhanced phase contrast microscopy. The first event was a momentary, localized, cytoplasmic contraction lasting approximately 1 s. This contraction was seen as a sudden unidirectional movement of visible organelles (mitochondria, spheroid bodies) toward the hyphal apex. During the contraction, there was a transitory sharp increase in refractive index in a localized area of cytoplasm in the apex or subapex of the cell. Within 5 s, the Spitzenkörper retracted from its normal position next to the apical pole and disappeared from view 20 to 50 s later. Hyphal elongation rate diminished sharply, and the typical distribution of organelles at the hyphal tip was disturbed. After 210-240 s, organelle distribution returned to normal, polarized growth resumed, but instead of one Spitzenkörper two new Spitzenkörper appeared, each giving rise to an apical branch. The second branch Spitzenkörper appeared with a 60- to 100-s delay. We did not observe the original Spitzenkörper dividing in two; instead, the new Spitzenkörper arose de novo from vesicle clouds that formed in the apical region next to the future site of branch emergence. In all instances that we examined, the dislocation and disappearance of the Spitzenkörper was preceded by cytoplasmic contractions. We therefore suspect the existence of an intimate connection between the cytoskeletal network and the Spitzenkörper. Accordingly, we propose that the apical branching phenotype in ramosa-1 is triggered by a molecular event that induces a transient alteration in cytoskeleton organization.
通过紫外线诱变分离出一株黑曲霉的顶端分支、温度敏感型突变体（ramosa-1）。Ramosa-1在23摄氏度时具有野生型形态，但转移到34摄氏度时会顶端分支。通过视频增强相差显微镜记录导致顶端分支的细胞学事件。第一个事件是瞬间的、局部的细胞质收缩，持续约1秒。这种收缩表现为可见细胞器（线粒体、球状体）朝着菌丝顶端的突然单向移动。在收缩过程中，细胞顶端或亚顶端细胞质的局部区域折射率短暂急剧增加。5秒内，顶体从其靠近顶端极的正常位置缩回，20至50秒后消失不见。菌丝伸长率急剧下降，菌丝顶端细胞器的典型分布受到干扰。210 - 240秒后，细胞器分布恢复正常，极性生长恢复，但不是一个顶体而是出现了两个新的顶体，每个顶体产生一个顶端分支。第二个分支顶体出现延迟60至100秒。我们没有观察到原来的顶体一分为二；相反，新的顶体是从靠近未来分支出现部位的顶端区域形成的囊泡云重新产生的。在我们检查的所有实例中，顶体的错位和消失之前都有细胞质收缩。因此，我们怀疑细胞骨架网络与顶体之间存在密切联系。据此，我们提出ramosa-1中的顶端分支表型是由诱导细胞骨架组织瞬时改变的分子事件触发的。
