Abstract
Auxin is a key regulator of plant growth and development, but the causal relationship between hormone transport and root responses remains unresolved. Here we describe auxin uptake, together with early steps in signaling, in Arabidopsis root hairs. Using intracellular microelectrodes we show membrane depolarization, in response to IAA in a concentration- and pH-dependent manner. This depolarization is strongly impaired in aux1 mutants, indicating that AUX1 is the major transporter for auxin uptake in root hairs. Local intracellular auxin application triggers Ca2+ signals that propagate as long-distance waves between root cells and modulate their auxin responses. AUX1-mediated IAA transport, as well as IAA- triggered calcium signals, are blocked by treatment with the SCFTIR1/AFB - inhibitor auxinole. Further, they are strongly reduced in the tir1afb2afb3 and the cngc14 mutant. Our study reveals that the AUX1 transporter, the SCFTIR1/AFB receptor and the CNGC14 Ca2+ channel, mediate fast auxin signaling in roots.
Highlights
Auxin is a key regulator of plant growth and development, but the causal relationship between hormone transport and root responses remains unresolved
To study the very earliest auxin responses in Arabidopsis root hairs, we employed electrophysiological techniques. This revealed that indole-3-acetic acid (IAA) depolarizes the plasma membrane in an AUX1dependent manner
On the basis of a stoichiometry of at least two H+ per IAA− and a chemiosmotic potential ranging from 180 to 300 mV, our data indicate that AUX1-mediated transport could theoretically accumulate auxin to 105 fold higher concentrations inside root hairs, as compared to the cell walls
Summary
Auxin is a key regulator of plant growth and development, but the causal relationship between hormone transport and root responses remains unresolved. Using intracellular microelectrodes we show membrane depolarization, in response to IAA in a concentrationand pH-dependent manner This depolarization is strongly impaired in aux[1] mutants, indicating that AUX1 is the major transporter for auxin uptake in root hairs. AUX1-mediated IAA transport, as well as IAA- triggered calcium signals, are blocked by treatment with the SCFTIR1/AFB - inhibitor auxinole They are strongly reduced in the tir1afb2afb[3] and the cngc[14] mutant. We report that early auxin-induced transient depolarizations represent AUX1-mediated uptake. We show that both the membrane electrical signal and a traveling Ca2+ wave require SCFTIR1/AFB receptor-based activation of plasma membrane calcium channels
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
