Helical growth

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

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. [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.] 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. [Hashimoto, T. 2002. Molecular genetic analysis of left-right handedness in plants. Philos. Trans. Roy. Soc. Biol. Sci. 357: 799-808.] It is not clear how helical growth mutants affect cell wall assembly of "Arabidopsis".

References

#Edwards, W. et al. 2007. The global trend in plant twining direction. Global Ecol. Biogeogr. 1-6.
#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.
#Hashimoto, T. 2002. Molecular genetic analysis of left-right handedness in plants. Philos. Trans. Roy. Soc. Biol. Sci. 357: 799-808.