Root Hairs

Ion channels and solute transporters in the plasma membrane of root hairs are proposed to control nutrient uptake, osmoregulation and polar growth. Here we analyzed the molecular components of potassium transport in Arabidopsis root hairs by combining K + -selective electrodes, reverse transcription-PCR, and patch-clamp measurements. The two inward rectifiers AKT1 and ATKC1 as well as the outward rectifier GORK dominated the root hair K + channel pool. Root hairs of AKT1 and ATKC1 loss-of-function plants completely lack the K + uptake channel or exhibited altered properties, respectively. Upon oligochitin-elicitor treatment of root hairs, transient changes in K + fluxes and membrane polarization were recorded in wild-type plants, while akt1-1 root hairs showed a reduced amplitude and pronounced delay in the potassium re-uptake process. This indicates that AKT1 and ATKC1 represent essential K K-subunits of the inward rectifier. Green fluorescent protein (GFP) fluorescence following ballistic bombardment with GORK promoter-GFP constructs as well as analysis of promoter-GUS lines identified this K + outward rectifier as a novel ion channel expressed in root hairs. Based on the expression profile and the electrical properties of the root hair plasma membrane we conclude that AKT1-, ATKC-and GORKmediated potassium transport is essential for osmoregulation and repolarization of the membrane potential in response to elicitors. ß

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Phosphorus (P) uptake and growth of a root hairless barley mutant (bald root barley, brb) and wild type in low‐ and high‐P soils

Gahoonia¹,

Nielsen²

2003

Plant Cell & Environment

110

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The recently isolated root-hairless mutant of barley ( Hordeum vulgare L), bald root barley, brb offers a unique possibility to quantify the importance of root hairs in phosphorus (P) uptake from soil. In the present study the ability of brb and the wild-type, barley genotype Pallas producing normal root hairs to deplete P in the rhizosphere soil was investigated and the theory of diffusion and mass flow applied to compare the predicted and measured depletion profiles of diffusible P. Pallas depleted twice as much P from the rhizosphere soil as brb . The P depletion profile of Pallas uniformly extended to 0.8 mm from the root surface, which was equal to the root hair length (RHL). The model based on the theory of diffusion and mass flow explained the observed P-depletion profile of brb, and the P depletion outside the root-hair zone of Pallas, suggesting that the model is valid only for P movement in rhizosphere soil outside the root-hair zone. In low-P soil (P in soil solution 3 m m m m M ) brb did not survive after 30 d, whereas Pallas continued to grow, confirming the importance of root hairs in plant growth in a P-limiting environment. In high-P soil (P in soil solution 10 m m m m M ) both brb and Pallas maintained their growth, and they were able to produce seeds. At the high-P concentration, RHL of the Pallas was reduced from 0.80 ± ± ± ± 0.2 to 0.68 ± ± ± ± 0.14 mm. In low-P soil, P-uptake rate into the roots of Pallas was 4.0 ¥ ¥ ¥ ¥ 10-1 and that of brb was 1.9 ¥ ¥ ¥ ¥ 10, which agreed well with the double amount of P depleted from the rhizosphere soil of Pallas in comparison with that of brb. In high-P soil, the P uptake rates into the roots of brb and Pallas were 3.3 and 5.5 ¥ ¥ ¥ ¥ 10, respectively. The results unequivocally confirmed that in a low-P environment, root hairs are of immense importance in P acquisition and plants survival, but under high-P conditions they may be dispensable. The characterization of phenotypes brb and Pallas and the ability to reproduce seeds offers a unique possibility of molecular mapping of QTLs and candidate genes conferring root-hair formation and growth of barley.

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Root Hairs

Cited by 5 publications

References 327 publications

Mechanisms of Cell Polarity Establishment and Polar Auxin Transport

Mechanisms of Cell Polarity Establishment and Polar Auxin Transport

K⁺ channel profile and electrical properties of Arabidopsis root hairs

Phosphorus (P) uptake and growth of a root hairless barley mutant (bald root barley, brb) and wild type in low‐ and high‐P soils

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Root Hairs

Cited by 5 publications

References 327 publications

Mechanisms of Cell Polarity Establishment and Polar Auxin Transport

Mechanisms of Cell Polarity Establishment and Polar Auxin Transport

K+ channel profile and electrical properties of Arabidopsis root hairs

Phosphorus (P) uptake and growth of a root hairless barley mutant (bald root barley, brb) and wild type in low‐ and high‐P soils

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K⁺ channel profile and electrical properties of Arabidopsis root hairs