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 results in the breaking of (usually radial) symmetry (biology). Resulting shapes may be left-handed or right-handed. Helical growth can arise naturally (e.g. as seen in tendrils or in twining plants [1] ) or artificially by mutation (Arabidopsis thaliana).
Helical growth of twining 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 twining plants show right-handed helices regardless of the hemisphere the plant is growing in.[2]
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.[3] In Arabidopsis thaliana 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.[4] It is not clear how helical growth mutants affect cell wall assembly of Arabidopsis thaliana.