Darwin connection IV [Or, nanotech item No. 2]

An investigation into the molecular basis of the adhesive that allows Hedera helix to cling to vertical structures shows that the nanoparticles identified in the adhesive are predominantly composed of arabinogalactan proteins.

I’m beginning to suspect that there is a rule – maybe unwritten, but a rule nonetheless – that English Victorian naturalist supreme, Charles Darwin (‘CD’) has to have had a hand in every biological phenomenon one might wish to study in the 20th and 21st centuries. After all, if you investigate anything relating to evolution, Darwin (and Wallace!) has already been there; auxins, and plant hormones more generally, Darwin (and son Francis) anticipated them; plant movements, Darwin & Son again; plant intelligence, etc. It’s no surprise therefore that the ‘spirit of Darwin’ is behind this month’s most tenacious item, ivy.

Hedera algeriensis
Hedera algeriensis. Image Digigalos / Wikipedia.

Picking up where CD left off 150 years previously (see p. 106 here), Yujian Huanga et al. have investigated the molecular basis of the adhesive that allows Hedera helix to cling to vertical structures. They show that the nanoparticles – previously identified in the adhesive – are predominantly composed of arabinogalactan proteins (AGPs), and propose that calcium-driven electrostatic interactions between the AGP nanoparticles generate cross-linking of the exuded adhesive. This favours its subsequent curing (hardening), which promotes ‘mechanical interlocking’ (i.e. adhesion) between the adventitious roots of the plant (which secrete the adhesive) and the surface of the substrate.

The team suggest that this work ‘may forward the progress toward understanding the general principles underlying diverse botanic adhesives’. Or, even ‘new approaches to wound healing, stronger armor for the military and maybe even cosmetics with better staying power’. Plant research that could make a real difference to so many varied aspects of the human experience, then.

However, you don’t necessarily need adhesives to provide adhesion, as Jiafu Tan et al. demonstrate with trichomes in cotton. When cotton and trichomes are mentioned together many people will think of so-called cotton fibres and their role as a clothing fibre. But, this work deals with development of the flower of Gossypium hirsutum and the trichomes present within the epidermis of its petals.

They show that these ‘hairs’ are essential for maintenance of correct flower bud shape through a mechanical entanglement of the trichomes on adjacent petals. This enmeshing anchors the edges to counter the opposing force generated by asymmetric expansion of overlapping petals. Whilst it is interesting to note that development of the commercial product Velcro® was inspired by plants, it’s quite another thing to discover that plants use a Velcro-like mechanism in their own biology. I don’t know about you, but I could get rather attached to this sort of work…

Further reading

J. J. Holland, D. Roberts, E. Liscum, 2009, 'Understanding phototropism: from Darwin to today', Journal of Experimental Botany, vol. 60, no. 7, pp. 1969-1978 http://dx.doi.org/10.1093/jxb/erp113

Tony Trewavas, 2016, 'Plant Intelligence: An Overview', BioScience, vol. 66, no. 7, pp. 542-551 http://dx.doi.org/10.1093/biosci/biw048

Yujian Huang, Yongzhong Wang, Li Tan, Leming Sun, Jennifer Petrosino, Mei-Zhen Cui, Feng Hao, Mingjun Zhang, 2016, 'Nanospherical arabinogalactan proteins are a key component of the high-strength adhesive secreted by English ivy', Proceedings of the National Academy of Sciences, vol. 113, no. 23, pp. E3193-E3202 http://dx.doi.org/10.1073/pnas.1600406113

Mingjun Zhang, Maozi Liu, Harry Prest, Steve Fischer, 2008, 'Nanoparticles Secreted from Ivy Rootlets for Surface Climbing', Nano Letters, vol. 8, no. 5, pp. 1277-1280 http://dx.doi.org/10.1021/nl0725704

Georg J. Seifert, Keith Roberts, 2007, 'The Biology of Arabinogalactan Proteins', Annual Review of Plant Biology, vol. 58, no. 1, pp. 137-161 http://dx.doi.org/10.1146/annurev.arplant.58.032806.103801

Li Tan, Allan M. Showalter, Jack Egelund, Arianna Hernandez-Sanchez, Monika S. Doblin, Antony Bacic, 2012, 'Arabinogalactan-proteins and the research challenges for these enigmatic plant cell surface proteoglycans', Frontiers in Plant Science, vol. 3 http://dx.doi.org/10.3389/fpls.2012.00140

Jiafu Tan, Sally-Anne Walford, Elizabeth S. Dennis, Danny Llewellyn, 2016, 'Trichomes control flower bud shape by linking together young petals', Nature Plants, vol. 2, no. 7, p. 16093 http://dx.doi.org/10.1038/nplants.2016.93

Martin Hülskamp, Swen Schellmann, 2009, 'Trichomes', Encyclopedia of Life Sciences http://dx.doi.org/10.1002/9780470015902.a0002071.pub2

Qing Zhao, Xiao-Ya Chen, 2016, 'Development: A new function of plant trichomes', Nature Plants, vol. 2, no. 7, p. 16096 http://dx.doi.org/10.1038/nplants.2016.96