Plant Cuttings

What are root hairs for?

A reasonable question. After all, root hairs – closed-tipped, tubular extensions of epidermal cells of roots – are numerous. So much so that, in what is now a classic paper, Howard Dittmer estimated that a single plant of rye (Secale cereal) may have 14,335,568,288 (!!) of these structures over the entirety of its root system. And the standard answer to that question is that they “greatly increase the surface area of roots. As such, they are widely believed to play an important role in plant nutrition by facilitating the absorption of water and nutrients” from the surrounding soil. But, is that all they do?

Root hairs
Root Hairs. Image: The New Student’s Reference Work / Wikipedia.

The suggestion that they might have a role in anchorage of the plant (a function mainly attributed to the root proper) was considered unlikely by Peter Bailey et al., at least in Arabidopsis and Allium cepa [onion]. However, that view has been challenged by Glyn Bengough et al.

Working with ‘normal’ plants of Zea mays, and mutants devoid of root hairs, they conclude that these epidermal outgrowths do assist in the anchorage of root tips to soil particles during soil penetration, and help roots to penetrate soils of relatively low soil density. Another interesting aspect of the Bengough et al. paper is that its literature review appears to be remarkably thorough, something that is often lacking in today’s scientific papers. And in so doing they highlight a particular problem in modern-day research where statements – which are factually correct – are frequently made without due credit being given to the originating author.

For example, in their paper’s Introduction Bengough et al. mention two 21st century papers that state that root hairs have an anchorage role, but which don’t cite sources supporting that notion. And, as every student who has failed to cite their sources in an assignment knows, this is extremely poor practice, which could result in a charge of plagiarism.

A third paper fared slightly better in citing Clifford Farr’s early 20th century contribution “Root Hairs and Growth” as evidence for that root-hair-anchorage notion. Unfortunately, Farr’s cited source – an 1883 paper in German by F Schwarz**– “appears to contain largely qualitative statements about the potential role of root hairs in anchorage, rather than a quantitative experimental study on anchorage” (Bengough et al.’s words, P Cuttings’ emphasis).

I suspect we’ve all done this sort of thing, provided a source that looks like it’s the correct one, but which we’ve not necessarily thoroughly checked to see if it is ‘fit for purpose’..? But, as evidence-based scientists we shouldn’t be satisfied with that, we ought to do a proper job. If literature is not correctly sourced – or not cited at all! – we risk losing an important element of science which is the connection with and continuity between that which has gone before and which provides the foundations upon which our present-day work is built. To use a building analogy, if the supporting foundations are not firm and properly in place, the stories that we try to construct thereupon are all the weaker.

They – Bengough et al. – also clearly distinguish their own work – on root-hair anchorage and root penetration of soil – from that of Bailey et al., which looked at uprooting of whole plants. But, isn’t this just splitting hairs? No, just careful, objective, scientifically rigorous work – a lesson from which we can all learn. Your journal club discussion question for this month then is: How far back should one follow the literature to ensure legitimate support for ‘facts’ one states in a scientific paper?

* Which poses another question, do aerial roots – e.g. those of tree-dwelling epiphytes such as certain orchids – have root hairs? Answers, please, on a post-card (remember them you ‘net natives’?) to: P Cuttings, The Phytoinvestigatorium, Leicester, The North, United Kingdom (just to the north–east of ‘Europe’).

** “Die Wurzelhaare der Pflanzen”, Untersuchungen aus dem Botanischen Institut zu Tübingen. Leipzig 1: 135–188, 1883 [and a big thank-you to Dr Gerhard Prenner of RBG Kew for sharing the link with me/you/us!]

References

Howard J. Dittmer, 1937, 'A Quantitative Study of the Roots and Root Hairs of a Winter Rye Plant (Secale Cereale)', American Journal of Botany, vol. 24, no. 7, p. 417 http://dx.doi.org/10.2307/2436424

P. V. Minorsky, 2002, Plant Physiology, vol. 129, no. 2, pp. 438-439 http://dx.doi.org/10.1104/pp.900038

P. H.J. Bailey, 2002, 'The role of root system architecture and root hairs in promoting anchorage against uprooting forces in Allium cepa and root mutants of Arabidopsis thaliana', Journal of Experimental Botany, vol. 53, no. 367, pp. 333-340 http://dx.doi.org/10.1093/jexbot/53.367.333

A. Glyn Bengough, Kenneth Loades, Blair M. McKenzie, 2016, 'Root hairs aid soil penetration by anchoring the root surface to pore walls', Journal of Experimental Botany, vol. 67, no. 4, pp. 1071-1078 http://dx.doi.org/10.1093/jxb/erv560

Clifford H. Farr, 1928, 'Root Hairs and Growth', The Quarterly Review of Biology, vol. 3, no. 3, pp. 343-376 http://www.jstor.org/stable/2808193

About the author

Nigel Chaffey

Nigel is a botanist and full-time academic at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany he contributes the monthly Plant Cuttings column to that august international botanical organ. His main goal is to inform (hopefully, in an educational, and entertaining way...) about plants and plant-people interactions.