On polar auxin transport in plant cells

Abstract

We present here explicit mathematical formulas for calculating the concentration, mass, and velocity of movement of the center of mass of the plant growth regulator auxin during its polar movement through a linear file of cells. The results of numerical computations for two cases, (a) the conservative, in which the mass in the system remains constant and (b) the non-conservative, in which the system acquires mass at one end and loses it at the other, are graphically presented. Our approach differs from that of Mitchison's (Mitchison 1980) in considering both initial effects of loading and end effects of substance leaving the file of cells. We find the velocity varies greatly as mass is entering or leaving the file of cells but remains constant as long as most of the mass is within the cells. This is also the time for which Mitchison's formula for the velocity, which neglects end effects, reflects the true velocity of auxin movement. Finally, the predictions of the model are compared with two sets of experimental data. Movement of a pulse of auxin through corn coleoptiles is well described by the theory. Movement of auxin through zucchini shoots, however, shows the need to take into account immobilization of auxin by this tissue during the course of transport.

Calcium deficiency and auxin transport in Cucurbita pepo L. seedlings

“…Polar auxin transport is considered, according to the hypothesis of chemiosmotic polar diffusion, to be energized by trans-plasma-membrane pH and electrical gradients with specificity and overall directionality dependent upon saturable carriers (Rubery and Sheldrake 1974;see Goldsmith 1977 for a review; Martin et al 1990). In a mechanism common to lipophilic weak acids, accumulation of indole-3-acetic acid (IAA) from the relatively acidic apoplast occurs by diffusion of the protonated species IAAH, with the impermeant IAA-anion being trapped in the cytoplasm.…”

Possible roles of auxin and zeatin for initiating the dwarfing effect of M9 used as apple rootstock or interstock

“…Recent research speculates that decreasing basipetal transport of IAA in dwarfing rootstocks might be related to an abnormal arrangement of auxin efflux proteins at the plasma membrane (Soumelidou et al 1994;Kamboj 1996;Kamboj et al 1997). PIN protein is a polar transport vector of auxin in plant tissues (Martin et al 1990). Eight PIN genes in Arabidopsis have been identified so far.…”

Homogenization of long-range auxin transport in plant tissues

“…Quantitative description of auxin transport has been based up-to-date on the chemiosmotic model of polar auxin diffusion, proposed in the mid 1970s, [7][8][9]. The chemiosmotic model uses the fact that IAA is a weak acid and in its ionic form it cannot freely pass through the cell membrane.…”