Helical growth

From Wikipedia, the free encyclopedia

A natural left-handed helix seen in a tendril of a climber plant. Tendrils often show helix reversals.

The term helical growth describes the expansion of fungal, algal or higher plant cells or organs leading to a twisted (i.e. helical) cell or organ shape. Helical growth can arise naturally (e.g. as seen in tendrils or in twinning plants) or artificially by mutation (Arabidopsis).

Helical growth of twinning plants is based on a nutational movement of stems (circumnutation). When such stems find support this nutational movement may become fixed into a helical winding. Most twinning plants show right-handed helices.

Helical growth of single cells, as seen in Phycomyces (Fungi) and Nitella (Characeae), is believed to be caused by a helical arrangement of microfibrils in the cell wall. This was suggested by birefringence analyses of cell walls. In Arabidopsis mutants helical growth is exhibited at the organ level. Mutant analysis strongly supports the idea that cortical microtubules have an important role in controlling the direction of organ expansion in plants. It is not clear whether these mutations have a direct effect on cell wall assembly.

Literature:

Edwards, W. et al. 2007. The global trend in plant twining direction. Global Ecol. Biogeogr. 1-6.

Hashimoto, T. 2002. Molecular genetic analysis of left-right handedness in plants. Philos. Trans. Roy. Soc. Biol. Sci. 357: 799-808.

Roelofsen, P.A. 1965. Ultrastructure of the wall in growing cells and its relation to the direction of growth. Adv. Bot. Res. 2: 69-149.