Auxin-induced, cell elongation

Rayle, D.L. Cleland, R.E. (1992). The acid growth theory of auxin-induced cell elongation is alive and well. Plant Physiol. 99,1271-1274. 

Auxin has been implicated in a bewildering array of growth responses. At the level of the cell, these responses involve rapid changes in cell expansion, effects on cell division and meristem activity, as well as differentiation of specific cell types [1]. In an effort to understand molecular aspects of auxin signaling, many researchers have focused on rapid biochemical responses associated with auxin-induced cell elongation. These include activation of a plasma membrane H -ATPase [2], changes in the behavior of ion channels... 

ABA inhibits auxin-induced cell elongation (Hemberg 1972 a, Philipson et al. 1973, Rehm and Cline 1973, Anker 1975) but, whereas many inhibitory... 

Cleland, R. E., 1968, Hydroxy proline formation and its relation to auxin-induced cell elongation in the Avena coleoptile. Plant Physiol. 43 1625-1630. 

Matthyssee and Phillips (20) isolated two nuclear proteins, from tobacco cells, that bound specifically to 2,4-D. Receptor proteins for auxins, kinetins, and GA have been found (21). Sub-cellular fractions from bean leaves were recently shown to bind abscisic acid (22). Preliminary experiments (22) indicated that maximum ABA binding activity coincides with the activities of membrane-bound Mg -dependent, K+-stimulated ATPase and glucan synthetase. Table I of Biswas and Roy (21) lists hormone receptor proteins reported in plant tissue. For a protein to qualify as a receptor molecule, it should have a high stereo-specific binding capacity (Kd 10 6 to 10 SM) for its particular hormone. In com coleoptiles, both IAA and NAA are equally effective in inducing cell elongations fractions of plasma membrane and endoplasmic reticular membrane contain receptor proteins with Kd values of 10 M to 10 M for auxins (5, 18). When one considers procedural... 

The plasma membranes of growing plant cells select to incorporate sugars, amino adds, ions and other low molecular weight compounds from the apoplastic space, and then, the cells have a certain level of osmotic pressure. The difference between their osmotic pressure and their wall pressure (=turgor pressure) is due to motive power (suction force) to suck water from the apoplastic space (Figure 1). The plant hormone auxin, which decreases the wall pressure in a growing plant cell, therefore induces cell elongation or expansion. 

There is some evidence to suggest that / -glucanases may play a role in the expansion of yeast cells in the absence of cell duplication. Yanagishima (61) and Shimoda et al. (62) discovered that a plant hormone, auxin (indole-3-acetic acid), induced cell elongation in auxin-... 

Metabolic disruptions may result in inhibition of cell enlargement. Key (9) found that actinomycin D, an inhibitor of DNA directed RNA synthesis (10), and puromycin, an inhibitor of protein synthesis, will prevent cell enlargement in soybean Glycine max L. Merr.) hypocotyls. Key concluded RNA and protein synthesis are essential for the process of cell elongation to proceed at a normal rate. The following year, Cleland reported the inhibition of cell enlargement caused by actinomycin D was not caused by an inhibition of auxin-induced cell wall loosening... 

Together with the even distribution of lAA (Table 1), these data lead to the conclusion that the phototropic movement of the radish hypocotyl is caused by a light-induced lateral distribution of three substances that differentially inhibit the auxin-regulated cell elongation at the two flanks. 

The cell wall defines the shapes of plant cells and restricts their elongation. Auxin-Induced loosening of the cell wall permits elongation. 

A second effect of ethylene is to alter the direction of cell enlargement in stems and roots [81]. By causing a change in orientation of cellulose microfibrils from transverse to random or longitudinal, it causes cells to swell up rather than elongate. As a result, stems and roots become shorter and thicker. The inhibition of stem and root growth induced by excess auxin is due in part to auxin-induced ethylene [82]. In a few tissues, such as... 

Both stem cell elongation and xylem differentiation are auxin-mediated processes. There has long been speculation that BRs act through alterations in the auxin response [109]. This is certainly not always the case, as BR induces elongation of soybean hypocotyls without activating any of the auxin-induced genes such as the SAUR genes [112]. On the other hand, one of the effects of BR in tomato hypocotyls appears to be to increase the sensitivity of the tissue to auxin [113]. Thus some BR effects may actually be mediated via auxin, while others are independent of auxin. 

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