Transport of auxin (indoleacetic acid) through lipid bilayer membranes

Gutknecht, John; Walter, Anne

doi:10.1007/bf01869353

Cited by 49 publications

(26 citation statements)

References 28 publications

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“…A modelling framework for polar auxin transport Auxin diffuses freely within cells and the cell wall and permeates cell membranes [19][20][21] . Most previous simulation models at the tissue/organ scale have mathematically combined diffusion and permeability into one effective flux 22 .…”

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Auxin transport is sufficient to generate a maximum and gradient guiding root growth

Grieneisen¹,

Marée³

et al. 2007

Nature

763

852

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The plant growth regulator auxin controls cell identity, cell division and cell expansion. Auxin efflux facilitators (PINs) are associated with auxin maxima in distal regions of both shoots and roots. Here we model diffusion and PIN-facilitated auxin transport in and across cells within a structured root layout. In our model, the stable accumulation of auxin in a distal maximum emerges from the auxin flux pattern. We have experimentally tested model predictions of robustness and self-organization. Our model explains pattern formation and morphogenesis at timescales from seconds to weeks, and can be understood by conceptualizing the root as an 'auxin capacitor'. A robust auxin gradient associated with the maximum, in combination with separable roles of auxin in cell division and cell expansion, is able to explain the formation, maintenance and growth of sharply bounded meristematic and elongation zones. Directional permeability and diffusion can fully account for stable auxin maxima and gradients that can instruct morphogenesis.

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Auxin transport is sufficient to generate a maximum and gradient guiding root growth

Grieneisen¹,

Marée³

et al. 2007

Nature

763

852

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“…No specific passive H+ conductance channels have been isolated from biological membranes. Postulated mechanisms explaining the high H+/OH-permeability in biological membranes (compared with that of other small cations) include linear watdr aggregates (24) and/or lipophilic weak acids (25) in membranes.…”

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Proton transport and cell function.

Ives¹,

Rector²

1984

J. Clin. Invest.

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T he past five years have witnessed an explosion of information on the many and varied roles of H+ transport in cell function. H+ transport is involved in three broad areas of cell function: (a) maintenance and alteration of intracellular pH for initiation of specific cellular events, (b) generation of pH gradients in localized regions of the cell, including gradients involved in energy transduction, and (c) transepithelial ion transport. These processes each involve one or more of several H+ translocating mechanisms. The first section of this review will discuss these H+ translocating mechanisms and the second part will deal with the cellular functions controlled by H+ transport. Mechanisms of H+/OH-TransportPrimary active H+ transport Primary active H' transport mechanisms consume energy directly for the translocation of HW. This energy can be derived from redox reactions, light, or ATP. Since most of the primary active H+ translocating processes are electrogenic, their action will produce only a membrane potential difference unless there is some provision in the membrane for counter ion movement. This is usually accomplished by a simple conductive pathway through which Cl-can move in the same direction as, or cations (e.g., K+ or Na+) can move in the opposite direction to H+ transport. As will be seen below, some ofthe active H' transport mechanisms do generate primarily a membrane potential difference, while others move significant amounts of acid across membranes. To date, there are no known primary active OHor HCO-transport mechanisms.H+ translocation by the electron transport chain. In the mitochondrion, three electron transport complexes (reduced nic-

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“…The concentration at the "receiving end" was held at zero for these calculations. Numerical values for all parameters for which independent estimates are available are as follows: indoleacetic acid diffusion coefficient D = 7 x 10-6 cm2 sec-1 (22); permeability coefficient of the undissociated acid PHA = 3.3 X 10-3 cm sec-1 (14,23); membrane voltage at the plasmalemma V = 100 mV (unpublished observation); wall pH = 5 (24,25); cytoplasmic pH The utility of the mathematical model is considerable, for although it is intended to describe a complex biological system, there remain only two related parameters forwhich there are no independent estimates. These are the values of PA-(or PA-) at the apical and basal ends of the cell.…”

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Mathematical analysis of the chemosmotic polar diffusion of auxin through plant tissues

Goldsmith

Martin

1981

Proc. Natl. Acad. Sci. U.S.A.

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Equations have been developed to describe the diffusional movement of a weak acid such as the auxin indoleacetic acid through a long file of vacuolated cells, where cellular accumulation is driven by the pH gradients across the cell membranes. If the permeability to the auxin anion is greater at one end of the cell than at the other, diffusional movement takes the form of polar transport, which exhibits: a nearly constant velocity either for the front or for a pulse of radioactive auxin, the capacity to move auxin against an external gradient of concentration, and a polar ratio that increases exponentially with the length of the section. The determinants of velocity include both diffusion through the vacuole and permeation steps at the cell membranes. Except Since the early quantitative descriptions of the transport of the endogenous plant growth hormone auxin* (1-3) its cellular basis has been elusive. Among its characteristics are (i) a polarity, in which auxin moves more effectively through tissues in one direction than in the other, with the polar ratio increasing approximately exponentially with distance (4-6); (ii) the ability to move auxin through a tissue against an external concentration gradient (3); and (iii) a velocity, evidenced by a nearly constant rate of travel of 10 or more mm hr-' of either the front (2, 4, 7-10) or a pulse of radioactively labeled auxin introduced at the apical end of a section (11). Various models involving differential secretion from the basal ends of the cells can account for the first two of these features, but there has been no convincing explanation for the third.The chemosmotic polar diffusion hypothesis draws ideas and observations from several sources and postulates that polar transport involves both steps of membrane permeation and diffusion through the cell (12). Uptake of auxin is pH dependent and appears to be driven by the pH difference between the inside of the cell and the acidic wall space. With a difference of 2 pH units, and with only the undissociated acid permeant, auxin can accumulate passively to an internal concentration more than 50 times greater than the external. If the auxin anion is also permeant, this accumulation will be reduced. The suggestion that the polarity of transport is caused by a greater permeability to the anion at the basal than at the apical end of each cell (13, 14) is a central feature of this hypothesis.Because neither cytoplasmic streaming (15) nor a lateral sheath of cytoplasm around the vacuole (16) is necessary to support transport, the auxin seems to cross the tonoplast and diffuse through the vacuole in traversing the length of each cell. The proposed path of auxin movement (Fig. 1) The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

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Transport of auxin (indoleacetic acid) through lipid bilayer membranes

Cited by 49 publications

References 28 publications

Auxin transport is sufficient to generate a maximum and gradient guiding root growth

Auxin transport is sufficient to generate a maximum and gradient guiding root growth

Proton transport and cell function.

Mathematical analysis of the chemosmotic polar diffusion of auxin through plant tissues

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