Root hairs increase the contact area of roots with soil and thereby enhance the capacity for solute uptake. The strict hair/non-hair pattern of Arabidopsis thaliana can change with nutrient deficiency or exposure to toxic elements, which modify root hair density.
Kohanová et al. assess the effects of root hairs on cadmium (Cd) uptake and translocation by comparing the Arabidopsis thaliana ecotype Columbia (Col-0) with mutants lacking root hairs (rhd6-1, cpc/try) and a mutant in which most rhizodermal cells develop into hairs (wer/myb23). The results indicate that root hair density can have a large effect on Cd accumulation in shoots, suggesting that the symplasmic pathway might play a significant role in the uptake and accumulation of this toxic element.
Kohanová, J., Martinka, M., Vaculík, M., White, P. J., Hauser, M.-T., & Lux, A. (2018). Root hair abundance impacts cadmium accumulation in Arabidopsis thaliana shoots. Annals of Botany. https://doi.org/10.1093/aob/mcx220