Field of Science

Moss Cell Walls Like Sponges

I came across this paper when cleaning off my computer desktop today. My labmate Juan Carlos sent it to me a while back. Upon stumbling across it again I decided to give it another read.

H. G. Edelmann, C. Neinhuis, M. Jarvis, B. Evans, E. Fischer and W. Barthlott. 1998. Ultrastructure and chemistry of the cell wall of the moss Rhacocarpus purpurascens (Rhacocarpaceae): a puzzling architecture among plants. Planta 206:315-321.

This paper focuses on the unique cell walls of leafy gametophyte of this moss. (For a little review of plant cell walls check out last week's post.) Rhacocarpus purpurascens grows in the high mountains of some tropical areas. It grows in large sheets that hang from rock faces and they pick up most of their water from fog. It has been known since the 1970's that the cell walls of this plant are structurally sponge-like. (Think your morning english muffin with a lot of nooks and crannies.) Typical plant cell walls are solid. This study sets out to analyze the walls using a number of methods.

They use some high-tech techniques such as electron microscopy (scanning and transmission), nuclear magnetic resonance (NMR) spectroscopy, and cell wall fractionation. Fancy techniques such as these are great. I use both types of electron microscopy in my own research. However I also enjoy techniques that have an elegant simplicity, which is how I would describe the two other experimental methods that they use (external water conduction and water-holding capacity). Basically these methods allow the authors to ask two questions: Can these sponge-like cell walls conduct water up the moss plant? and How absorptive are these cell walls? In these two experiments they compared Rhacocarpus purpurascens to two or three other moss species that have solid cell walls.

For external water conduction the placed the bottom end of the moss stem into a tube of water and measured how far up the stem the water traveled. They found that the water did not move very far up the stem in Rhacocarpus purpurascens, whereas the other species became hydrated all the way to the tip. Thus the cell walls are not functioning in water conduction.

For water holding capacity plants were dried, soaked in water for 10 minutes and then weighed. Contrary to what you might have anticipated, Rhacocarpus purpurascens held 25% less water than the other species per gram of dry weight. (So it does not appear to be acting as a sponge, which was my initial thought when reading the paper.) However a majority of the water that this plant has access to is in the form of fog. It is not submerged when growing in its native habitat. The authors anticipate that the wall characteristics allow the available moisture to be absorbed quickly and moved inside the cell.

I think that it is pretty cool when scientific questions can be asked and answered using simple techniques. It just goes to show that scientific experimentation is accessible to more than university researchers.

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