Control of Elongation in the Bean Hypocotyl by the Ability of the Hypocotyl Tip to Transport Auxin

Jacobs, William P.

doi:10.1002/j.1537-2197.1950.tb11042.x

Cited by 19 publications

(3 citation statements)

References 7 publications

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“…Diffusible ( z transported) auxin rather than extractable material is correlated with elongation (e. g. JACOBS, 1950). This observation seems to support the third possibility.…”

Section: Isupporting

confidence: 61%

Auxin movement in corn coleoptiles

Hertel

Flory

1968

Planta

113

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Movement of radioactive auxins was analysed in corn coleoptile sections. The results support the idea that processes involved in the transport of indoleacetic acid (IAA) are specific for growth-promoting auxins.Inhibition of IAA transport by triiodobenzoic acid is caused by a reversible block of the exit; the auxin held back remains in the transport pool. The observed increase in immobilization may be a secondary effect caused by the increased concentration of free IAA in the tissue.Auxin molecules are most likely transported by anon-covalent mechanism. IAA and naphthaleneacetic acid (NAA) move through the cell and exit as free molecules. A search for a transient auxin complex, chaseable as required for any transport carrier intermediate, yielded negative results. No(18)O was lost from NAA labeled with(18)O in the carboxyl group during transport of the auxin through coleoptile tissue.After application of IAA to auxin-depleted tissue, the transport rate undergoes oscillations with a period length of ca. 25 min.The movement of the auxin 2.4-dichlorophenoxyacetic acid which is usually sluggish, increased several times if some IAA was added. Auxin, thus, stimulates its own transport.A model is discussed in which auxin-binding to the plasma membrane and reversible changes of membrane conformation may provide a basis for active secretion and for the observed cooperativity.

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“…Diffusible ( z transported) auxin rather than extractable material is correlated with elongation (e. g. JACOBS, 1950). This observation seems to support the third possibility.…”

Section: Isupporting

confidence: 61%

Auxin movement in corn coleoptiles

Hertel

Flory

1968

Planta

113

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“…For many years, "diffusible auxin" has been equated with growth-active auxin (8,16). It is presumably free auxin which can react with "growth-active sites" (6), while that which is cytologically compartmentalized or chemically bound cannot do so (unpublished data).…”

Section: Discussionmentioning

confidence: 99%

Emergent Growth

Parrish

Davies²

1977

Plant Physiol.

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Restoration of oxygenated conditions following 15 minutes to 2 hours of anoxia causes light-grown pea (Pisum sativum L. var. Alaska) stem segments to elongate 100 to 200% more than continuously aerated segments. This "emergent growth" response takes place in the presence of 5 mM F-, an inhibitor of anaerobic respiration; therefore, a build-up of glycolytic products does not appear to be the mechanism underlying emergent growth. "Acid growth" does not appear to account directly for the hyperelongation, as extracellular pH does not drop following a return to aerobic conditions. Studies with 14C-indoleacetic acid indicate that auxin is freed from some previously unavailable pool during 02-limited treatments. We suggest, therefore, that emergent growth is a response to auxin which is released during anaerobiosis: the newly mobile or diffusible auxin promoting growth when 02 is no longer limiting.Anaerobic treatments of light-grown pea stem segments modify elongation both during and after the period of 02 deprivation (21,22). One of the most striking phenomena is a postanaerobic enhancement of growth rates. The burst of growth following anoxia is such that elongation surpasses that of continuously aerated segments by 100 to 200%. We have named this hyperelongation phenomenon "emergent growth" (21). Emergent growth may be operationally defined as the elongation (during and following inhibitory treatments) in excess of control segments. Elongation which catches but does not surpass that of the control has previously been defined as "stored growth" (26).We report here that emergent growth is apparently an auxinmediated response. The evidence further suggests that growth in auxin-induced systems is regulated by a sequestering or compartmentalization of the hormone. We intend to present more complete evidence for the latter concept in a subsequent report. MATERIALS AND METHODSExpanding third internodes were excised from 8-to 10-dayold glasshouse-grown peas (Pisum sativum L. var. Alaska). One-cm segments were placed in 1 or 20 mm phosphate buffer (pH 6.2) and aerated vigorously until further use. Growth measurements and anoxic treatments were achieved as previously described (22,23). Ten segments were stacked in a buffer-filled chamber and their growth monitored with an angular position transducer. To produce anoxic conditions, N2 was bubbled through the chamber and in the reservoir which supplied solu-I Present address: Department of Agronomy, University of Nebraska, Lincoln, Neb. 68583. tions to the chamber. F-was used as a glycolytic inhibitor in some growth measuring experiments at concentrations of up to 20 mm NaF, but the higher levels markedly inhibited aerobic as well as anaerobic growth. Routinely, 5 mm NaF was used and 5 mM NaCl employed as the control.To test whether emergent growth might be related to "acid growth" (14,27), pH studies were performed (24). Twenty-five to 30 1-cm segments were stripped of their epidermis and placed in a beaker with 5 ml of 1 mm buffer (initial pH 6.2) and the pH of the...

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“…3,4,8). Furthermore, in green shoots of plants past the seedling stage, even cases of acropetal movement were discovered.…”

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confidence: 99%

Polarity of Indoleacetic Acid in young Coleus Stems

Jacobs¹

1977

Plant Physiol.

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Young internodes of Coklus blumci Benth. have long been known for their sizable amount of acropetal indoleacetic acid movement. However, plants of the same done, under improved growing conditions, now show almost absolute basipetal polarity of 14C-indoleacetic acid, as measured by liquid scintillation counting of 14C in the receiver cylinders of agar.The ratio of basipetal to acropetal movement is now as much as 85:1, instead of the 3:1 ratio found years ago under conditions providing dower growth.Although auxins such as IAA were first known for their unvarying and strongly polar basipetal movement through the organs of etiolated seedlings such as Avena coleoptiles, later work showed that this movement was subject to regulation (e.g. 3, 4, 8). Furthermore, in green shoots of plants past the seedling stage, even cases of acropetal movement were discovered. The most thoroughly investigated of these are the 3:1 ratio of basipetal to acropetal IAA movement through sections cut from young internodes of Coleus (first found with bioassay measurements by Jacobs [5,6], then confirmed with radioisotope counting of 14C_ IAA by Naqvi and Gordon [23] and Leopold and de la Fuente [19]) and the increasing acropetal movement of IAA that occurs through sections of bean petioles of increasing age (20,21). The auxin-type herbicide, 2,4-D, gave similar results in bean petioles (9,14,21).Is this acropetal movement through excised sections merely an artifact of excision? For bean petioles the only evidence on this point comes from elongation measurements after such sections were provided with IAA from the base only or from the apex only: basally applied IAA produced relatively more growth as the petioles from which the sections were cut were progressively older (10, 21). For young Coleus internodes the evidence that the 3:1 ratio of IAA movement is meaningful has been related somewhat more closely to the intact plant: if vascular strands in matching internodes were cut, the regeneration of tracheary cells was mostly basipetal, but with some strands regenerating acropetally from the cut strand below the wound (5)-thus qualitatively paralleling the 3:1 ratio of IAA movement. Quantitative data in support of the physiological significance of acropetal IAA movement came from experiments in which all leaves below the regenerating internode were excised in one set of plants and that set compared with a set which had all leaves excised above the regenerating internode. Leaves had already been shown to be the main source of endogenous auxin in the Coleus shoot (5), hence those wounds presumably had auxin available to them only from above or only from below, respectively. (5,7,15, 27), the conclusion was drawn that the acropetal movement of IAA, observed in transport sections cut from internode #2, also occurred in the more nearly intact plant, where it caused the regeneration of the 5.6 strands of tracheary cells found 1 week after the leaves above the wound were excised (6).To understand more about the polarity of hormone movement...

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Control of Elongation in the Bean Hypocotyl by the Ability of the Hypocotyl Tip to Transport Auxin

Cited by 19 publications

References 7 publications

Auxin movement in corn coleoptiles

Auxin movement in corn coleoptiles

Emergent Growth

Polarity of Indoleacetic Acid in young Coleus Stems

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