Regulation of root hair density by phosphorus availability in Arabidopsis thaliana

Abstract

We characterized the response of root hair density to phosphorus (P) availability in Arabidopsis thaliana. Arabidopsis plants were grown aseptically in growth media with varied phosphorus concentrations, ranging from 1 mmol m−3 to 2000 mmol m−3 phosphorus. Root hair density (number of root hairs per mm of root length) was analysed starting at 7 d of growth. Root hair density was highly regulated by phosphorus availability, increasing significantly in roots exposed to low‐phosphorus availability. The initial root hairs produced by the radicle were not sensitive to phosphorus availability, but began to respond after 9 d of growth. Root hair density was about five times greater in low phosphorus (1 mmol m−3) than in high phosphorus (1000 mmol m−3) media. Root hair density decreased logarithmically in response to increasing phosphorus concentrations within that range. Root hair density also increased in response to deficiencies of several other nutrients, but not as strongly as to low phosphorus. Indoleacetic acid (IAA), the auxin transport inhibitor 2‐(p‐chlorophenoxy)‐2‐methylpropionic acid (CMPA), the ethylene precursor 1‐aminocyclopropane‐1‐carboxylic acid (ACC), and the ethylene synthesis inhibitor amino‐oxyacetic acid (AOA) all increased root hair density under high phosphorus but had very little effect under low phosphorus. Low phosphorus significantly changed root anatomy, causing a 9% increase in root diameter, a 31% decrease in the cross‐sectional area of individual trichoblasts, a 40% decrease in the cross‐sectional area of individual atrichoblasts, and 45% more cortical cells in cross‐section. The larger number of cortical cells and smaller epidermal cell size in low phosphorus roots increased the number of trichoblast files from eight to 12. Two‐thirds of increased root hair density in low phosphorus roots was caused by increased likelihood of trichoblasts to form hairs, and 33% of the increase was accounted for by changes in low phosphorus root anatomy resulting in an increased number of trichoblast files. These results show that phosphorus availability can fundamentally alter root anatomy, leading to changes in root hair density, which are presumably important for phosphorus acquisition.

Phytotoxicity of petroleum-contaminated soil and bioremediated soil on Allophylus edulis

“…This happens because the increase in root hairs maximizes absorptive surface (Esau 1977), and may also be related to the low availability of phosphorus (Ma et al 2001). It is known that soils with hydrocarbons exhibit lower water retention (Merkl et al 2005), and that bioremediated soils exhibit lower concentrations of nitrogen and phosphorus (Hutchinson et al 2001), that was recorded in this experiment with A. edulis (Tab.…”

Physiological and molecular alterations in plants exposed to high [CO2] under phosphorus stress

“…Also the development of 'proteoid' roots, special structures in certain plant families that release large amounts of organic acids, has been attributed to P-deficiency (Adams et al, 2002). Another adaptive strategy in response to P deficiency is increased root hair length and density, which increases total root surface area at minimal carbon cost to improve P uptake (Ma et al, 2001;Lynch and Brown, 2001;Gahoonia and Nielsen, 2003;Gahoonia and Nielsen, 2004). In comparison to the structural adaptations listed above, an even more carbon-efficient strategy to acquire higher amounts of P is to promote mycorrhizal symbioses (Pandey et al, 2005a).…”

Enantioselective Oxidative Damage of Chiral Pesticide Dichlorprop to Maize

“…Therefore, dense root hairs can facilitate plant uptake of nutrients, benefiting plant growth, whereas sparse root hairs will reduce nutrient uptake and cause plant damage. 25 Inhibition rates on seed germination, seedling biomass, and root and shoot elongation were investigated, and they increased significantly with an increasing exposure concentration of DCPP, irrespective of the chiral configuration ( Table 1). All of the inhibition indexes are in the following order: (R)-DCPP > (rac)-DCPP > (S)-DCPP treatments.…”