The Movement of Plant Hormones: Auxins, Gibberellins, and Cytokinins

Jacobs, William P.

doi:10.1007/978-3-642-65406-0_91

Cited by 18 publications

(7 citation statements)

References 16 publications

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“…Auxin moves in a specific transport system basipetally in shoots and acropetally in roots (Goldsmith, 1969). There is evidence that gibberellins (Jacobs, 1972) and abscisic acid can move basipetally in shoots. Both auxin and gibberellins (Phillips, 1972a, b) become redistributed in tissues as a result of phototropic and geotropic stimulation.…”

Section: The Control Of Hormone Production and Distributionmentioning

confidence: 99%

The Production of Hormones in Higher Plants

Sheldrake¹

1973

Biological Reviews

106

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SUMMARY Although much is known about the effects of plant hormones and their role in the control of growth and differentiation, little is known about the way in which hormone production is itself controlled or about the cellular sites of hormone synthesis. The literature on hormone production is discussed in this review in an attempt to shed some light on these problems. The natural auxin of plants, indol‐3yl‐acetic acid (IAA) is produced by a wide variety of living organisms. In animals, fungi and bacteria it is formed as a minor by‐product of tryptophan degradation. The pathways of its production involve either the transamination or the decarboxylation of tryptophan. The transaminase route is the more important. In higher plants auxin is also produced as a minor breakdown product of trypto phan, largely via transamination. In some species decarboxylation may occur but is of minor importance. Tryptophan can also be degraded by spontaneous reaction with oxidation products of certain phenols. The unspecific nature of the enzymes involved in IAA production and the probable importance of spontaneous, nonenzymic reactions in the degradation of tryp to phan make it unlikely that auxin production from tryptophan can be regulated with any precision at the enzymic level. The limiting factor for auxin production is the availability of tryptophan, which in most cells is present in insufficient quantities for its degradation to occur to a significant extent. Tryptophan levels are, however, considerably elevated in cells in which net protein breakdown is taking place as a result of autolysis. An indole compound, glucobrassicin, occurs in Brassica and a number of other genera. It breaks down readily to form a variety of products including indole aceto‐nitrile, which can give rise to IAA. There is, however, no evidence to indicate that glucobrassicin is a precursor of auxin in vivo. Conjugates of IAA, e.g. IAA‐aspartic acid and IAA‐glucose, are formed when IAA is supplied in unphysiologically high amounts to plant tissues. These and other IAA conjugates occur naturally in developing seeds and fruits. There is no persuasive evidence for the natural occurrence of IAA‐protein complexes. Tissues autolysing during prolonged extraction with ether produce IAA from tryptophan released by proteolysis. IAA is produced in considerable quantities by autolysing tissues in vitro. During the senescence of leaves proteolysis results in elevated levels of trypto phan. Large amounts of auxin are produced by senescent leaves. Coleoptile tips have a vicarious auxin economy which depends on a supply of IAA, IAA esters and other compounds closely related to IAA from the seed. These move acropetally in the xylem and accumulate at the coleoptile tip. The production of auxin in coleoptile tips involves the hydrolysis of IAA esters and the conversion of labile, as yet unidentified compounds, to IAA. There is no evidence for the de novo synthesis of IAA in coleoptiles. Practically all the other sites of auxin production are sites of both meristematic ...

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Section: The Control Of Hormone Production and Distributionmentioning

confidence: 99%

The Production of Hormones in Higher Plants

Sheldrake¹

1973

Biological Reviews

106

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“…The observed differences in the efficiency of transport of the three hormones agrees with other studies where the physiological significance of the translocated hormone was investigated. Thus an efficient acropetally polarized transport of IAA in roots was found (Bowen et al, 1972, Hartung and Phillips 1974, Jacobs 1972, Shaw and Wilkins 1974 whereas the basipetal transport was very low and was ascribed to diffusion (Bowen et al, 1972), Basipetal movement of IAA occurs, however, below the growing zone of the root (Davies et al, 1976), The more efficient basipetal transport of BAP, and especially of gibberellin, is supported by the well-established hypothesis that the root system is a major source of gibberellins and cytokinins which are transported to the shoot in the transpiration stream Reid 1968, Kende andSitton 1967), However, it should be noted that in the present study the translocation of the label from various radiochemicals, rather than the movement of the applied substances, was studied. Also, some losses of radioactivity from the entire system could occur.…”

Section: Resultsmentioning

confidence: 99%

“…However, relatively little attention has been directed towards the problems of hormone transport in intact plants, and this is especially the case with transport in the root. The sometimes contradictory results on the direction and pathway of transport may well result from differences between irt vivo and itt vitro systems (Davies and Mitchell 1972, Morris e/fl/, 1968, Pilet 1968, It has been shown that IAA moves with a strong acropetal polarity through root sections of several species (Kirk andJacobs 1968, Scott andWilkins 1968), and that this acropetal transport occurs only in the presence of stelar tissues (Bowen et al 1972, Hartung and Phillips 1974, Shaw and Wilkins 1974, However, when IAA was applied exogenously to roots of intact plants, both acropetal and basipetal transport has been demonstrated (Davies andMitchell 1972, Konings andGayadin 1971), Transport of gibberellin in roots was studied only with isolated segments, and was found to be strongly basipetal (Hartung andPhillips 1974, Jacobs andPruett 1973), and restricted to the stele (Hartung and Phillips 1974), With regard to cytokinin transport, a basipetal movement was found in roots of intact plants (Chvojka et al 1971, Gordon et al 1974, Lagerstedt and Langston 1967, Mozes and Altman 1977, while the nature of transport in isolated sections of shoot and root has been debated (Black and Osborne 1965, Jacobs 1972, Radin and Loomis 1974, Very few studies on the transport of abscisic acid and of ethyiene in roots are available (Hartung andBehl 1974, Jackson andCampbell 1975),…”

Section: Introductionmentioning

confidence: 99%

Comparative Basipetal Transport of 6‐Benzylaminopurine‐8‐¹⁴C, Gibberellin A₃‐³H, IAA‐2‐¹⁴C, and Sucrose‐¹⁴C in the Root of Intact Citrus aurantium Seedlings

Altman

Mozes

1977

Physiologia Plantarum

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The transport and distribution of IAA‐2‐14C, gibberellin A3‐3H, 6‐benzylaminopurine‐8‐14C and sucrose‐14C (U) were studied in whole seedlings of Citrus aurantium L. after “replacing” the root tip with the solution of radiochemicals. All four substances were transported basipetally in the root and were distributed to the stem and leaves. The pattern of distribution of the label from 6‐benzylaminopurine was similar to that of sucrose, while a considerably larger amount of gibberellin A3 was transported to basal regions of the root, away from the tip, and into the shoot. Contrary to these three substances, the basipetal transport of IAA in the root was very low, and the majority of the label was retained in the terminal sections of the root. It is suggested that the different efficiencies at which various hormones move in the transpiration stream in the root may be an important factor in the attainment of a certain balance of hormones in the shoot.

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“…Root initiation on cuttings always shows the upper-lower .polarity. This rooting polarity is eaused by the downward transloeation of the IAA (Jacobs, 1972(Jacobs, , 1978Scott & Most, 1972). However, this polar translocation is not only evidence for the upperlower polarity, but also for outer-inner polarity, as the leading poles of the two kinds of polarity coincide.…”

Section: Iaamentioning

confidence: 99%

Sensitivity to phytohormones determined by outer‐inner polarity of higher plants: An overall model for phytohormone action

Liu

Tillberg

1984

Plant Cell & Environment

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A generalized model of the higher plant body is proposed in order to assemble the discrete knowledge of the actions, and sites of biosynthesis, of phytohormones. In this model, we attempt to explain the differential sensitivities of different tissues. With this model most effects of plant hormones appear to be reasonable, and even expected. The model is based on a new anatomical and physiological classification of plant tissue. In higher plants the integration of an outer‐inner polarity and an upper‐lower polarity plays a major role in phytohormone behaviour. Plant tissues and organs which are derived from the cortex of paleophytes (the bud, the mesophyll of the leaf, the cortex of the stem, and the root cap) are classified as the outer pole of the plant. On the other hand, tissues and organs which are derived from the stele of paleophytes (the root, the stele of the shoot, and the vein of the leaf), are classified as the inner pole. It is suggested that tissue sensitivities to phytohormones are mainly determined by the outer‐inner polarity. Phytohormones which are synthesized from one pole act on the other, whereas they exert either much less or no effect, or an inverse effect on their own pole. This is shown for both promoters and inhibitors of the phytohormones for both cortical and stelar vegetative tissues of plants.

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The Movement of Plant Hormones: Auxins, Gibberellins, and Cytokinins

Cited by 18 publications

References 16 publications

The Production of Hormones in Higher Plants

The Production of Hormones in Higher Plants

Comparative Basipetal Transport of 6‐Benzylaminopurine‐8‐¹⁴C, Gibberellin A₃‐³H, IAA‐2‐¹⁴C, and Sucrose‐¹⁴C in the Root of Intact Citrus aurantium Seedlings

Sensitivity to phytohormones determined by outer‐inner polarity of higher plants: An overall model for phytohormone action

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The Movement of Plant Hormones: Auxins, Gibberellins, and Cytokinins

Cited by 18 publications

References 16 publications

The Production of Hormones in Higher Plants

The Production of Hormones in Higher Plants

Comparative Basipetal Transport of 6‐Benzylaminopurine‐8‐14C, Gibberellin A3‐3H, IAA‐2‐14C, and Sucrose‐14C in the Root of Intact Citrus aurantium Seedlings

Sensitivity to phytohormones determined by outer‐inner polarity of higher plants: An overall model for phytohormone action

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Comparative Basipetal Transport of 6‐Benzylaminopurine‐8‐¹⁴C, Gibberellin A₃‐³H, IAA‐2‐¹⁴C, and Sucrose‐¹⁴C in the Root of Intact Citrus aurantium Seedlings