Non-invasive quantification of endogenous root auxin transport using an integrated flux microsensor technique

• Published in: The Plant journal : for cell and molecular biology Vol. 63; no. 6; pp. 1004 - 1016
• Main Authors: McLamore, Eric S, Diggs, Alfred, Calvo Marzal, Percy, Shi, Jin, Blakeslee, Joshua J, Peer, Wendy A, Murphy, Angus S, Porterfield, D. Marshall
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.09.2010; Blackwell Publishing Ltd; Blackwell
• Subjects: auxin; Biochemistry; Biological and medical sciences; Biological Transport - drug effects; Biosensing Techniques - methods; Botany; Corn; Electrodes; Fundamental and applied biological sciences. Psychology; Glycolates - pharmacology; Hormones; Indoleacetic Acids - metabolism; integrated flux; maize; non-invasive; Phthalimides - pharmacology; Plant physiology and development; Plant Roots - drug effects; Plant Roots - metabolism; roots; self-referencing electrode/microsensor; Sensors; Zea mays - drug effects; Zea mays - metabolism; self-referencing electrode/microsensor; Auxin; Endogenous; non-invasive; Microsensor; Root; Flux; Plant growth substance; integrated flux; Technique; roots; maize
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/j.1365-313X.2010.04300.x

Indole-3-acetic acid (IAA) is a primary phytohormone that regulates multiple aspects of plant development. Because polar transport of IAA is an essential determinant of organogenesis and dynamic tropic growth, methods to monitor IAA movement in vivo are in demand. A self-referencing electrochemical microsensor was optimized to non-invasively measure endogenous IAA flux near the surface of Zea mays roots without the addition of exogenous IAA. Enhanced sensor surface modification, decoupling of acquired signals, and integrated flux analyses were combined to provide direct, real time quantification of endogenous IAA movement in B73 maize inbred and brachytic2 (br2) auxin transport mutant roots. BR2 is localized in epidermal and hypodermal tissues at the root apex. br2 roots exhibit reduced shootward IAA transport at the root apex in radiotracer experiments and reduced gravitropic growth. IAA flux data indicates that maximal transport occurs in the distal elongation zone of maize roots, and net transport in/out of br2 roots was decreased compared to B73. Integration of short term real time flux data in this zone revealed oscillatory patterns, with B73 exhibiting shorter oscillatory periods and greater amplitude than br2. IAA efflux and influx were inhibited using 1-N-naphthylphthalamic acid (NPA), and 2-naphthoxyacetic acid (NOA), respectively. A simple harmonic oscillation model of these data produced a correlation between modeled and measured values of 0.70 for B73 and 0.69 for br2. These results indicate that this technique is useful for real-time IAA transport monitoring in surface tissues and that this approach can be performed simultaneously with current live imaging techniques.