Botany Article Summary

In the article "The Microbial World: Fungal tip growth and hyphal tropisms" from the Institute of Cell and Molecular Biology, The University of Edinburgh, 1995, Jim Deacon explains hyphal tropisms. He explains hyphal tropisms by giving specific examples of plants that undergo this process. He also explains spore tropisms and the tropism of rust germ tubes.

A tropism is an orientation response of a hypha to an external stimulus. The first example given of a hyphal tropism is of a fungus like plant named Pythium aphanidermatum. The plant was allowed to germinate in water. On one side of the cyst clusters there was a nutrient rich agar block. The zoospore cysts in the plants of the oomycota group, like Pythium aphanidermatum, have fixed point of germination. As a result the you hyphae originally emerged and started growing in all directions but then reorientated and grew towards the nutrient rich agar. This tropism in a fungus-like group of plants is rare seeing as the spores in most fungus like plants do not have fixed points of germination.

The spores of most fungus-like plants can germinate from almost any point. Many times external factors will play a role in determining what point a spore will germinate from. An example of this type of spore tropism is the plant Idriella bolleyi from the deuteromycota group. The spores of Idriella bolleyi were sprayed onto the roots of living and dead aseptic wheat seedlings that were growing on had been growing on a thin film of water agar. The spores growing on the surface of the living root hair almost always grew away from the root hair, while the spores growing on the surface of the dead root hair almost always grew toward the root hair.

There are several different things that make up hyphal tropisms. Jim Deacon explains these different processes and gives specific examples of plants that undergo these processes. He discusses the unique tropism of a fungus-like