Thesis-PDF - IAP/TU Wien

Pellicle
The pellicle of E. gracilis could be imaged with AFM with excellent resolution and
detail. For example in Fig. 6.9 the apical part of such a cell is shown, revealing the
flagellum, a deepened shape of the reservoir and an embossed shape of a crystalline
storage grain (paramylum). The visibility of the reservoir and the paramylum grain
results from the flattening of the cell due to the drying process where the algal
pellicle sinks into the reservoir and relaxes over the hard paramylum grain.
In Fig. 6.10, the middle part of an E. gracilis, the course of the pellicular
strips is very distinct. They are arranged diagonally and are very uniform in
thickness and direction. The pellicle usually grows as a left-handed spiral. Some
paramylums show as cameo shapes in the pellicle.
Figure 6.9: Apical part of an E. gracilis cell. a flagellum, b reservoir, c
cameo shape of a paramylum grain. Image size 20 × 20 µm 2 , Intermittent
contact mode AFM image, Amplitude trace.
Zooming into the details of a typical pellicle of an E. gracilis cell, the articulations
between the strips can be seen showing lubricant material features. In Fig.
6.11, a detail view of a group of pellicle strips is given. The small spots distributed
mainly between the strips are mucilage, biological lubricant produced by the algae.
The alga is able to actively slide its pellicle strips against each other in order to
change its shape.
A high resolution detail of previous figure is given in Fig. 6.12 that shows again
the mucilage between the strips as well as microtubuli that presumably stem from
another disrupted cell. Euglenoid mucilage, a polysaccharide network specially
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