The transport and metabolism of (14)C-labelled indoleacetic acid in intact pea seedlings

The effects of green and chemically-synthesized copper oxide nanoparticles on the production and gene expression of morphinan alkaloids in Oriental poppy

Oriental poppy (Papaver orientale L.) belonging to the Papaveraceae family, has the capacity to synthesize a wide range of benzylisoquinoline alkaloids (BIAs). This experiment was conducted to investigate the effects of green and chemical copper oxide nanoparticles (CuO NPs) elicitors on oxidative stress and the BIAs biosynthesis pathway in the cell suspension culture of P. orientale. This research shows that both green and chemical CuO NPs at concentrations of 20 mg/L and 40 mg/L, induce oxidative stress in the cell suspension of P. orientale by increasing the production of H2O2 and the activity of antioxidant enzymes. The comparison of treatments revealed that utilizing a lower concentration of CuO NPs (20 mg/L) and extending the duration of cell suspension incubation (up to 48 h) play a more influential role in inducing the expression of the BIAs biosynthesis pathway genes (PsWRKY, TYDC, SalSyn, SalR, SalAT, T6ODM, COR and CODM) and increasing the production of morphinan alkaloids (thebaine, codeine, and morphine). The overarching results indicate that the concentration of CuO NPs and the duration of cell treatment have a more significant impact than the nature of CuO NPs in inducing oxidative stress and stimulating the expression of the BIAs pathway genes.

Both induction and morphogenesis of cyst nematode feeding cells are mediated by auxin

Various lines of evidence show that local changes in the auxin concentration are involved in the initiation and directional expansion of syncytia induced by cyst nematodes. Analysis of nematode infections on auxin-insensitive tomato and Arabidopsis mutants revealed various phenotypes ranging from complete inhibition of syncytium development to a decrease in hypertrophy and lateral root formation at the infection site. Specific activation of an auxin-responsive promoter confirmed the role of auxin and pointed at a local accumulation of auxin in developing syncytia Disturbance of auxin gradients by inhibiting polar auxin transport with N-(1-naphthyl)phtalamic acid (NPA) resulted in abnormal feeding cells, which were characterized by extreme galling, massive disordered cell divisions in the cortex, and absence of radial expansion of the syncytium initial toward the vascular bundle. The role of auxin gradients in guiding feeding cell morphogenesis and the cross-talk between auxin and ethylene resulting in a local activation of cell wall degrading enzymes are discussed.

Auxin metabolism in the root apical meristem

Within the root meristem of flowering plants is a group of mitotically inactive cells designated the quiescent center (QC). Recent work links the quiescent state to high levels of the growth regulator auxin that accumulates in the QC via polar transport. This in turn results in elevated levels of the enzyme ascorbic acid oxidase (AAO), resulting in a reduction of ascorbic acid (AA) within the QC and mitotic quiescence. We present evidence for additional interactions between auxin, AAO, and AA, and report that, in vitro, AAO oxidatively decarboxylates auxin, suggesting a mechanism for regulating auxin levels within the QC. We also report that oxidative decarboxylation occurs at the root tip and that an intact root cap must be present for this metabolic event to occur. Finally, we consider how interaction between auxin and AAO may influence root development by regulating the formation of the QC.

Gravitropism of roots: an evaluation of progress during the last three decades

The response of plant roots to gravity has fascinated many botanists since the early days of plant physiology and much research has been devoted to the elucidation of the sequence of events between the physical reception of gravity and the visible growth response. In the last few decades the ideas on the graviresponse of roots have changed profoundly and much progress has been made in understanding parts of the process. One of the reasons for writing this review was my curiosity to know what has happened since the time I myself was involved in the study of root geotropism, as it was called, about 30 years ago. Some excellent reviews have appeared since then, e.g. Audus (1975), Jackson & Barlow (1981) and Moore & Evans (1986), which were more restricted in scope and, moreover, there have been several fascinating developments. The aim of this review is to discuss briefly all aspects of the graviresponse of roots and the progress made in understanding during the last three decades. Some data on other plant organs are included where appropriate.

On polar auxin transport in plant cells

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.

Applicability of the chemiosmotic polar diffusion theory to the transport of indol-3yl-acetic acid in the intact pea (Pisum sativum L.)

The transport of exogenous indol-3yl-acetic acid (IAA) from the apical tissues of intact, light-grown pea (Pisum sativum L. cv. Alderman) shoots exhibited properties identical to those associated with polar transport in isolated shoot segments. Transport in the stem of apically applied [1-(14)C]-or [5-(3)H]IAA occurred at velocities (approx. 8-15 mm·h(-1)) characteristic of polar transport. Following pulse-labelling, IAA drained from distal tissues after passage of a pulse and the rate characteristics of a pulse were not affected by chases of unlabelled IAA. However, transport of [1-(14)C]IAA was inhibited through a localised region of the stem pretreated with a high concentration of unlabelled IAA or with the synthetic auxins 1-napthaleneacetic acid and 2,4-dichlorophenoxyacetic acid, and label accumulated in more distal tissues. Transport of [1-(14)C]IAA was also completely prevented through regions of the intact stem treated with N-1-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid.Export of IAA from the apical bud into the stem increased with total concentration of IAA applied (labelled+unlabelled) but approached saturation at high concentrations (834 mmol·m(-3)). Transport velocity increased with concentration up to 83 mmol·m(-3) IAA but fell again with further increase in concentration.Stem segments (2 mm) cut from intact plants transporting apically applied [1-(14)C]IAA effluxed 93% of their initial radioactivity into buffer (pH 7.0) in 90 min. The half-time for efflux increased from 32.5 to 103.9 min when 3 mmol·m(-3) NPA was included in the efflux medium. Long (30 mm) stem sections cut from immediately below an apical bud 3.0 h after the apical application of [1-(14)C]IAA effluxed IAA when their basal ends, but not their apical ends, were immersed in buffer (pH 7.0). Addition of 3 mmol·m(-3) NPA to the external medium completely prevented this basal efflux.These results support the view that the slow long-distance transport of IAA from the intact shoot apex occurs by polar cell-to-cell transport and that it is mediated by the components of IAA transmembrane transport predicted by the chemiosmotic polar diffusion theory.

Regulation of auxin transport in pea (Pisum sativum L.) by phenylacetic acid: inhibition of polar auxin transport in intact plants and stem segments

The transport of [(14)C]phenylacetic acid (PAA) in intact plants and stem segments of light-grown pea (Pisum sativum L. cv. Alderman) plants was investigated and compared with the transport of [(14)C]indiol-3yl-acetic acid (IAA). Although PAA was readily taken up by apical tissues, unlike IAA it did not undergo long-distance transport in the stem. The absence of PAA export from the apex was shown not to be the consequence of its failure to be taken up or of its metabolism. Only a weak diffusive movement of PAA was observed in isolated stem segments which readily transported IAA. When [1-(14)C]PAA was applied to a mature foliage leaf in light, only 5.4% of the (14)C recovered in ethanol extracts (89.6% of applied (14)C) had been exported from the leaf after 6.0 h. When applied to the corresponding leaf, [(14)C]sucrose was readily exported (46.4% of the total recovered ethanol-soluble (14)C after 6.0 h). [1-(14)C]phenylacetic acid applied to the root system was readily taken up but, after 5.0 h, 99.3% of the recovered (14)C was still in the root system.When applied to the stem of intact plants (either in lanolin at 10 mg·g(-1), or as a 10(-4) M solution), unlabelled PAA blocked the transport through the stem of [1-(14)C]IAA applied to the apical bud, and caused IAA to accumulate in the PAA-treated region of the stem. Applications of PAA to the stem also inhibited the basipetal polar transport of [1-(14)C]IAA in isolated stem segments. These results are consistent with recent observations (C.F. Johnson and D.A. Morris, 1987, Planta 172, 400-407) that no carriers for PAA occur in the plasma membrane of the light-grown pea stem, but that PAA can inhibit the carrier-mediated efflux of IAA from cells. The possible functions of endogenous PAA are discussed and its is suggested that an important role of the compound may be to modulate the polar transport and-or accumulation by cells of IAA.

The influence of small direct electric currents on the transport of auxin in intact plants

When a d.c. potential of 9.0 V was applied to the stem of intact pea seedlings (Pisum sativum L. cv. Meteor and cv. Alderman) via 10 mM KCl-soaked filter paper electrodes placed ca. 50 mm apart the stem passed a steady current of 15-20 μA (resistance ca. 100 kΩ cm(-1)). The basipetal transport of [1-(14)C]IAA applied to the apical bud was completely inhibited over the portion of the stem through which current flowed and (14)C-labelled compounds accumulated in the vicinity of the upper electrode. The inhibition of transport was independent of the polarity of the applied potential. The basipetal transport of IAA in the stem above the electrode was not affected.Labelled auxin accumulated at the upper electrode both as unchanged IAA and as a compound tentatively identified as indol-3yl-acetyl aspartic acid (IAAsp). These compounds were only slowly remobilised when the current was interrupted. However, the ability of the transport system to move freshly-applied IAA was rapidly and fully restored when the potential was removed. No injury to the plant was detected after maintaining a current flow for up to 72 h. No leakage of (14)C-labelled compounds into the KCl solution bathing the electrodes was detected.

Cell length, light and(14)C-labelled indol-3yl-acetic acid transport inPisum satisum L. andPhaseolus vulgaris L

The putative auxin-transporting cells of the intact herbaceous dicotyledon are the young, differentiating vascular elements. The length of these cells was found to be considerably greater in dwarf (Meteor) than in tall (Alderman) varieties ofPisum sativum L., and to be greater in etiolated than in light-grown plants ofP. sativum cv Meteor andPhaseolus vulgaris L. cv Mexican Black. Under given light conditions during transport these large differences in cell length did not influence the shapes of the transport profiles or the velocity of transport of(14)C-labelled indol-3yl-acetic acid (IAA) applied to the apical bud. However, in both etiolated and light-grown bean and dwarf pea plants the velocity of transport in darkness was ca. 25% lower than that in light. Under the same conditions of transport velocities in bean were about twice those observed in the dwarf pea. Exposure to light during transport increased the rate of export of(14)C from the labelled shoot apex in green dwarf pea plants but not in etiolated plants. The light conditions to which the plants were exposed during growth and transport had little effect on the rates of uptake of IAA from the applied solutions. The results indicate that the velocity of auxin transport is independent of the frequency of cell-to-cell interfaces along the transport pathway and it is suggested that in intact plants auxin transport is entirely symplastic.

Effects of temperature and sink activity on the transport of (14)C-labelled indol-3yl-acetic acid in the intact pea plant (Pisum sativum L.)

The velocity and intensity of basipetal transport of (14)C-labelled indol-3yl-acetic acid (IAA) applied to the apical bud of the intact pea plant were influenced by the temperature to which the stem was exposed and were not influenced by changes in the temperature of the root system when this was controlled independently between 5°C and 35°C. The velocity of transport increased steadily with temperature to a maximum in excess of 35°C and then fell sharply with further increase in temperature. The Q10 for velocity, determined from Arrhenius plots, was low (ca. 1.3). Transport intensity increased to a maximum at about 25°C (Q10=2.2) and then declined gradually with further increase in temperature. It is suggested that transport velocity and transport intensity are controlled independently.The characteristics of auxin transport through the stem were not affected by removal of the root system, or by the withdrawl of root aeration. Labelled IAA did not pass a region of the stem cooled to about 1.0°C, or through a narrow zone of stem tissue killed by heat treatment. In the latter case the heat treatment was shown not to interfere with the upward transport of water in the xylem. Labelled IAA continued to move into, and to accumulate in, the tissues immediately above a cooled or heat-killed region of the stem. It was concluded that the long-distance basipetal transport of auxin through the stem of the intact plant is driven by the transporting cells themselves and is independent of the activity of sinks for the transported auxin.The fronts of the observed tracer profiles in the stem were closely fitted by error function diffusion analogue curves. However, diffusion of IAA alone could not account for the observed characteristics of the transport and it is suggested that the curvilinear fronts of the profiles resulted from a diffusive mixing of exogenous IAA (or IAA-carrier complexes) with endogenous IAA already in the transport pathway.

Accumulation of (14)C from exogenous labelled auxin in lateral root primordia of intact pea seedlings (Pisum sativum L.)

When [(14)C]indol-3yl-acetic acid was applied to the apical bud of 5-day old dwarf pea seedlings which possessed unbranched primary roots, a small amount of (14)C was transported into the root system at a velocity of 11-14 mm h(-1). Most of the (14)C which entered the primary root accumulated in the young lateral root primordia, including the smallest detectable (20-30 mm from the primary root tip). In older (8-d old) seedlings in which the primary root bore well-developed lateral roots, (14)C also accumulated in the tertiary root primordia. In contrast, little (14)C was detected in the apical region of the primary root or, in older plants, in the apices of the lateral roots.

Auxin gradient along the root of the maize seedling

[5-(3)H]Indol-3yl-acetic acid (IAA) applied to the shoot apices of intact 6-day-old maize (Zea mays L.) plants moved into the primary root and accumulated at the root apex. IAA from the shoot could partially satisfy the requirement of the primary root for IAA for growth.

Transport of exogenous auxin in two-branched dwarf pea seedlings (Pisum sativum L.) : Some implications for polarity and apical dominance

Dwarf pea plants bearing two cotyledonary shoots were obtained by removing the epicotyl shortly after germination, and the patterns of distribution of (14)C in these plants was investigated following the application of [(14)C]IAA to the apex of one shoot. Basipetal transport to the root system occurred, but in none of the experiments was (14)C ever detected in the unlabelled shoot even after transport periods of up to 48 h. This was true both of plants with two equal growing shoots and of plants in which one shoot had become correlatively inhibited by the other, and in the latter case applied whether the dominant or subordinate shoot was labelled. In contrast, when [(14)C]IAA was applied to a mature foliage leaf of one shoot transfer of (14)C to the other shoot took place, although the amount transported was always low. Transport of (14)C from the apex of a subordinate shoot on plants bearing one growing and one inhibited shoot was severely restricted compared with the transport from the dominant shoot apex, and in some individual plants no transport at all was detected. Removal of the dominant shoot apex rapidly restored the capacity of the subordinate shoot to transport apically-applied [(14)C]IAA, and at the same time led to rapid cambial development and secondary vascular differentiation in the previously inhibited shoot. Applications of 1% unlabelled IAA in lanolin to the decapitated dominant shoot maintained the inhibition of cambial development in the subordinate shoot and its reduced capacity for auxin transport. These results are discussed in relation to the polarity of auxin transport in intact plants and the mechanism of correlative inhibition.

The movement of 2,4-dichlorophenoxy acetic acid in root segments of Pisum sativum L. : II. Immobilisation and oscillations in uptake and transport

An acropetal polarisation of the movement of 2,4-dichlorophenoxy acetic acid (2,4-D) through subapical segments of Pisum seedling primary roots has been monitored throughout a 60 h transport period in darkness at 25° C using [1-(14)C]2,4-D and [2-(14)C]2,4-D. Uptake of 2,4-D does not proceed at a constant rate; periods in which the amount of (14)C in the root segments and receiver blocks increases rapidly are followed by periods in which the amount of radioactivity remains relatively constant or declines slightly. These oscillations do not appear to be related to the time of day at which the experiments are begun or ended. Immobilisation and degradation of 2,4-D during transport in the segments seems to be low. Replacement of [1-(14)C]2,4-D donor blocks after 25 h by blocks containing unlabelled 2,4-D results in continued transport of the compound into receiver blocks, with only small amounts of (14)C remaining in the root tissues. Radioactivity is also exported from the segments into the blocks used to replace the donor blocks, with larger amounts being exported into the blocks applied to the apical ends than into those applied to the basal ends of the segments. This radioactivity may be taken-up again by the segments but more (14)C is exported into these blocks towards the end of the experiments. The possibility of regular oscillations in uptake and movement of 2,4-D in Pisum root segments is discussed.

The rapid non-polar transport of auxin in the phloem of intact Coleus plants

Indole-3-acetic acid (IAA) is transported from a nearly mature leaf throughout an intact Coleus blumei Benth. plant in the phloem. A buffered solution of both (14)C-methylene-labeled indoleacetic acid ([(14)C]IAA) and [6-(3)H]glucose was supplied in a glass capillary to the distal end of a severed main lateral vein of the leaf. Both labeled sugar and auxin move rapidly through the plant at velocities of ca. 16-20 cm h(-1) with closely similar, exponential profiles. This translocation is nonpolar; both auxin and sugar move upwards to the apex and young expanding leaves as well as downwards to the base of the shoot. Neither tracer appears in mature leaves; this eliminates the possibility that they enter the xylem. At the end of the transport period, 80-90% of the radioactivity recovered from various portions of the plants supplied with [(14)C]IAA is still identical chromatographically with IAA. In microautoradiographs prepared by techniques that minimize loss and redistribution of soluble compounds, radioactivity from [(3)H]IAA is concentrated in the phloem of the midrib and petiole of the fed leaf. A ring of triiodobenzoic acid (TIBA) strongly inhibits the polar auxin transport in sections isolated from the ringed region but does not significantly affect auxin translocation in the phloem of intact plants. TIBA does, however, reduce the entry of auxin into the collecting veins of the leaf. Thus steps in auxin transport sensitive to TIBA may occur during transfer through the leaf or into the phloem, but not during long distance translocation in the phloem.

Basipetally polarised transport of [(3)H]gibberellin A 1 and [ (14)C]gibberellin A 3, and acropetal polarity of [ (14)C]indole-3-acetic acid transport, in stelar tissues of Phaseolus coccineus roots

Movement of both [(3)H]GA1 and [(14)C]GA3 through root segments from P. coccineus seedlings was basipetally polarised. The basipetal/acropetal ratio of radioactivity from [(3)H]GA1 in agar receiver blocks was 9.2 for apical, elongating segments, and 4.0 for more basal, non-elongating segments. Polarity of gibberellin transport was restricted to the stele, and absent from cortical tissues. Transport of [(14)C]IAA through root segments to agar receivers was preferentially acropetal, particularly so in the stele. Despite the existence of basipetal polarity of gibberellin transport in the root, [(3)H]GA1 injected into cotyledons moved into and acropetally along the seedling root.

The specificity of auxin transport in intact pea seedlings (Pisum sativum L.)

When eight (14)C-labelled auxin and non-auxin compounds were applied to the apical buds of intact dwarf pea seedlings (Pisum sativum L.), only [1-(14)C]indoleacetic acid ([(14)C]IAA) and α-[1-(14)C] naphthaleneacetic acid ([(14)C]NAA) underwent appreciable basipetal transport during the first 24 h; over a longer period (72 h) considerable basipetal transport of the auxin [1-(14)C]2,4-dichlorophenoxyacetic acid ([(14)C]2,4-D) also occurred, but at a very much lower velocity (ca. 1.4-2.2 mm·h(-1)). The movement of 2,4-D possessed many of the characteristics of a typical auxin transport. During uptake and transport IAA and NAA were extensively metabolised to the corresponding aspartates, and to ethanol-insoluble/NaOH-soluble compounds; little metabolism of 2,4-D was observed. None of the non-auxin compounds applied (sorbose, sucrose, leucine, adenine and kinetin) underwent appreciable basipetal transport from the apical bud. All but sorbose were extensively metabolised by the apical tissues. Little metabolism of sorbose itself was detected.The results suggest that the long-distance basipetal auxin transport system from the apical bud of intact plants is specific for auxins; the specificity may result from the affinity of auxins for specific transport sites.

[Transport, distribution and metabolism of auxin in Vicia faba L. roots after application of [(14)C]IAA or [ (3)H]IAA to the apical bud]

After application of [2-(14)C]IAA or [(3)H]IAA to the apical bud of intact young broad-beans, the movement of labelled auxin into the roots was followed by liquid scintillation counting and by autoradiographic analyses. Its metabolism was studied by chromatography, and its pathways by autoradiographic analyses coupled with ringing experiments or removal of the stele.The movement of [(14)C]IAA or [(3)H]IAA was characterized by a high retention of radioactivity in tissues, particularly in very young plants. The speed, which did not exceed 9 mm·h(-1) in old roots, appeared the slower the younger the plants were. However, it seemed possible that small quantities of IAA or its derivates went into sieve tubes in which they moved downwards faster. In the apical part of the root the labelled IAA was more quickly transformed than in the other parts of this organ. 24 h after the application of the IAA, the labelled molecules gathered more densely in the cap itself than in apical meristem.At least 2/3 of the applied auxin moved within the stele, which in a crosssection represents only 1/7 of the whole area. In the older part of the root, the cambial zone located between mature phloem and mature xylem was the preferred pathway of IAA transport, although it is a zone where the hormone is immobilized, used and metabolised. In the younger part of the root, the whole stele was the preferred pathway. Therefore, the auxin is in a privileged situation to take part in the regulation of various processes, especially in the development of secondary vascular tissue, more particularly of xylem.

Auxin and ethylene control of growth in epidermal cells of Pisum sativum: A biphasic response to auxin

The effects of IAA and ethylene have been compared on the development of epidermal cells in intact shoots of etiolated pea plants. In the expanding sub-apical region ethylene has little effect on cell volume over 24 h but between 12 and 24 h rapid increases occur in cell wall thickening, part of which is due to the deposition of longitudinally orientated microfibrils adjacent to the plasmalemma. During this period, there is a rise in the levels of extractable cytoplasmic peroxidase. Two distinct phases of growth occur in response to IAA: an initial stimulation of cell expansion which causes the wall to stretch and decrease inthickness relative to the control (this phase is considered to be the true auxin response), followed some 12 h later by a decline in the rate of expansion and a thickening of the cell walls. During the first phase, peroxidase levels are depressed by IAA but a stimulation occurs after prolonged treatment. The effects observed in the second phase are believed to be mediated by ethylene which is synthesized at a high rate following treatment with IAA. Epidermal cells of mature internodes show a slight first phase expansion in response to IAA and their walls become a little thinner. Ethylene, however, has no effect on either expansion or wall thickness of mature cells even though the activity of peroxidase and the level of hydroxyproline-rich protein in the wall increases. These findings are discussed in relation to the dual regulation of cell growth by auxin and ethylene and the biphasic nature of the auxin response.

Variation and metabolism of abscisic acid in pea seedlings during and after water stress

When pea seedlings lose about 5% of their water content the abscisic acid ((+)-ABA) level of the shoots increases ca. 20 times and the level of bound ABA, in all probability ABA-glucose, ca.7-10 times. After watering both ABA and bound ABA contents decrease within 24-48 h to the level in the control plants.After application of (±)-[2-(14)C] ABA to wilted pea shoots at the time of watering radioactive substances appear in the water-soluble, ether-insoluble fraction of ethanolic extracts and increase with time whereas radioactivity in the acidic ether fraction decreases. The neutral ether fraction remains free of radioactivity. Three radioactive zones, A, B, and C, are seen on chromatograms of the water-soluble fraction. A increases considerably within the entire experimental time, whereas B increases in the first 4-8 h after application and subsequently decreases. The third substance, C, which releases free ABA after hydrolytic treatment, does not change during the experiment. Chromatograms of the acidic ether fraction yield ABA and a substance staying at the origin, possibly phaseic acid and/or dihydrophaseic acid. Only the activity of ABA decreases during the experiment.

[Transport of [(14)C] auxin from young pods of Vicia faba L]

After the injection of [(14)C]indole acetic acid (IAA) into very young pods of broad-bean (Vicia faba L.) the movement of the (14)C in the peduncle and stem was followed by autoradiography. In samples with only one young pod the basipetal transport was always clearly dominant. Most of the radioactivity was found in the bundles, particularly in the outer region of the bundle and also in the inner region (protoxylem parenchyma). The progression of the tracer was relatively complex. The rate of movement of the radioactive «front» could be as much as 2 cm·h(-1) but most of the (14)C moved towards the base at rates clearly less than that of the «front». Chromatograms with several solvent systems showed that IAA was the main or the only mobile radioactive substance. During transport, a part of IAA was converted into indole-3-aldehyde (IAld) and indole-3-acetyl-aspartic acid (IAAsp). IAAsp and possibly also IAld, which were found mainly near the donor pod, seemed immobile. This work is part of a study on the interchange of phytohormones between fruit and plant.

Auxin transport in intact pea seedlings (Pisum sativum L.): The inhibition of transport by 2,3,5-triiodobenzoic acid

The application of 2,3,5-triiodobenzoic acid (TIBA, 10 mg·g(-1) in lanolin) to the stem of intact pea seedlings (Pisum sativum L.) inhibited the basipetal transport of (14)C from indoleacetic acid-1-(14)C (IAA-1-(14)C) applied to the apical bud, but not the transport of (14)C in the phloem following the application of IAA-1-(14)C or sucrose-(14)C to mature foliage leaves. It was concluded that fundamentally different mechanisms of auxin transport operate in these two pathways.When TIBA was applied at the same time as, or 3.0 h after, the application of IAA-1-(14)C to the apical bud, (14)C accumulated in the TIBA-treated and higher internodes; when TIBA was applied 24.0 h before the IAA-1-(14)C, transport in the stem above the TIBA-treated internode was considerably reduced. TIBA treatments did not consistently influence the total recovery of (14)C, or the conversion of free IAA to indoleaspartic acid (IAAsp). These results are discussed in relation to the possible mechanism by which TIBA inhibits auxin transport,.Attention is drawn to the need for more detailed studies of the role of the phloem in the transport of endogenous auxin in the intact plant.

Transport of indoleacetic acid in intact roots of Phaseolus coccineus

Indoleacetic acid (IAA)-5-(3)H (2×10(-9)) was applied to intact roots of Phaseolus coccineus seedlings at the apex or 2 cm above the apex, and the movement of IAA-(3)H and its metabolites traced by sectioning and chromatography. Basipetal movement of label occurred for 2 cm or less, declining exponentially, and the amount increased with time. Acropetal transport from above the apex showed quantitatively less movement of radioactivity. After a 6h treatment period a decline of label occurred in the first 0.5cm, below which there was a long distance movement of small amounts of label, mainly in IAA, towards the apex where the label concentrated by a factor of approximately 2. Short-distance basipetal movement consisted of about equal amounts of IAA and metabolites, and only metabolites were found in areas more basipetal than 2cm. Label from solutions of sucrose-(14)C and (3)H2O followed the same general pattern of movement as label from IAA-(3)H, except that acropetal movement of water showed a steady decrease in the amount of label as the distance from the area of application increased. The short distance basipetal transport of label with the breakdown of IAA-(3)H indicates that the extent of basipetal movement was limited by catabolic processes. The acropetal pattern of IAA-(3)H movement with the concentration of the transported material close to the apex, is possibly the result of transport in the phloem.

Pathways of auxin transport in the intact pea seedling (Pisum sativum L.)

When small colonies of the pea aphid [Acyrthosiphon pisum (Harris)] were established on the stem of Meteor Dwarf Pea seedlings (Pisum sativum L.), (14)C was found in the honeydew 4.5 h after applying IAA-1-(14)C to a fully-expanded foliage leaf. In contrast, no activity was found in the honeydew or aphids 4.5 h after the application of IAA-1-(14)C to the intact apical bud even though the internode upon which the aphids were feeding contained high levels of (14)C. The lack of radio-activity in aphids feeding on stems to which IAA-1-(14)C was applied via the apical bud was found not to be influenced by the internode position or by the transport interval allowed (up to 24 h).Radioactivity derived from either foliar or apical applications of IAA-1-(14)C was not transported through stem tissues killed by heat treatment. Xylem function was shown not to be impared by the heat treatment employed.It was concluded that the long-distance transport of IAA from the apical bud of intact pea seedlings does not take place in the phloem sieve tubes involved in the transport of metabolites from foliage leaves, or in the non-living tissues of the xylem.

Patterns of translocation and metabolism of (14)C-labelled IAA in the phloem of Willow

When 2-(14)-C-labelled IAA was applied to an isolated segment of Willow via a bark abrasion the pathway of transport of this compound was found to be located in the sieve elements as evidenced by the pattern of activity found in honeydew excreted by individuals of Tuberolachnus salignus (Gmelin) feeding on the segment.Further experiments have established that polarity of transport of (14)C-IAA occurs in a basipetal direction when isolated segments of willow are orientated in a vertical position, with the morphological apex uppermost. No polarity was found when segments were orientated in a vertical position with the morphological base uppermost, or when the segments were orientated in a horizontal position. The metabolism of (14)C-IAA was also studied with respect to orientation. It was shown that the conversion rate of IAA to IAA aspartate was influenced by the orientation of the segment. It is considered that this is not a direct effect of orientation on the rate of metabolism of IAA.

Decarboxylation and transport of auxin in segments of sunflower and cabbage roots

The movement of (14)C from indole-3-acetic acid (IAA) (14)C has been examined in 5 mm root segments of dark-grown seedlings of Helianthus annuus and Brassica oleracea. Contaminants from distilled water, phosphate buffer and the razor-blade cutter increase the decarboxylation of IAA-(14)C, and cutting of root segments results in an activation of IAA-destroying enzymes at the cut surfaces. When these sources of errors were eliminated the following was shown: a) Both in sunflower and cabbage there is a slight acropetal flux of (14)C through the root segments into the agar receiver blocks. The amount of (14)C found in the receiver blocks increases with the lenght of the transport period. b) When the root segments, after the transport period, are cut in two equal parts and these assayed separately, the amounts of (14)C in the two parts indicate a greater acropetal than basipetal transport. c) The total radioactivity of the receiver blocks is in part due to IAA-(14)C and in part to (14)CO2, the latter being a result of enzymatic destruction of auxin. d) Addition of ferulic acid, an inhibitor of IAA oxidases, to the receiver blocks markedly inhibits the decarboxylation of IAA-(14)C and thus increases the amount transported. This effect is more pronounced after a 20 hr than after a 6 hr transport period.

Characterization of cytokinin action on enzyme formation during the development of the photosynthetic apparatus in rye seedlings : Enzymes of the reductive and oxidative pentose phosphate cycles

The action of cytokinin on the formation of photosynthetic enzymes in rye seedlings, which was described earlier, is further characterized by studying the interactions of kinetin with specific inhibitors of protein synthesis and with auxins. The combined action of cytokinin and auxin simultaneously affects enzymes of the oxidative pentose phosphate cycle which show a definite relationship to the appearance of the photosynthetic apparatus. 1. The formation of the photosynthetic enzyme carboxydismutase (EC 4.1.1.39) in rye seedlings can be almost completely prevented by chloramphenicol, but is also strongly inhibited by cycloheximide. These effects of chloramphenicol and cycloheximide cannot be overcome by the application of kinetin. 2. Plastid growth as well as the formation of photosynthetic enzymes (carboxydismutase; NADP-dependent glyceraldehydephosphate dehydrogenase, EC 1.2.1.9) are selectively curtailed in dark- or light-grown rye seedlings by treatment with relatively high concentrations of auxins like 3-indoleacetic acid, α-naphthalene-acetic acid (NAA) or 2,4-dichlorophenoxyacetic acid. 3. The inhibition of plastid growth and enzyme formation can be overcome to an increasing extent by applying increasing amounts of kinetin to young seedlings simultaneously with the NAA. Conversely, the promoting effect of kinetin on the formation of photosynthetic enzymes can be lowered by simultaneous application of NAA. In older seedlings the effect of NAA is no longer reversed by kinetin. An interpretation of the particularly high cytokinin requirement for the synthesis of photosynthetic enzymes in the seedlings is proposed. The appearance of the photosynthetic enzymes in the dark and in the light is accompanied by a decline in the rate of accumulation of key enzymes of the oxidative pentose phosphate cycle, especially glucose-6-phosphate dehydrogenase (EC 1.1.1.49). This effect is not due to a simple insufficiency of nutrients. Moreover, applications of glucose-6-phosphate or 6-phosphogluconate did not suggest an inducing effect of these substrates on their corresponding enzymes. No further increase of glucose-6-phosphate dehydrogenase can be achieved by application of either kinetin or NAA alone. But the formation of this enzyme continues at a high rate and reaches nearly twice the maximal activity of the controls when high concentrations of kinetin and NAA are applied simultaneously. It is concluded that a specific effect of the auxin and the diminished competition of the plastids for the promoting effect of kinetin contribute to the increased formation of glucose-6-phosphate dehydrogenase.The role of cytokinins in the control of the described enzymes is discussed.

Light and the transport and metabolism of indoleacetic acid in normal and albino dwarf pea seedlings

The patterns of transport and metabolism of IAA-2-(14)C applied to the apices of intact normal and albino dwarf pea seedlings were essentially similar under given light conditions. Light greatly reduced the decarboxylation of the applied IAA and stimulated the synthesis of indoleaspartic acid (IAAsp) in both normal and albino plants.In light considerably more (14)C was exported from the apices of normal than albino plants; this result was attributed to the reduced capacity of the transport system in the latter.The specific activity of (14)C in the stem decreased logarithmically with increasing distance from the treated apex. Light increased the steepness of the logarithmic profile. These results are discussed in relation to the rate of immobilization of IAA along the transport pathway by conversion to IAAsp.No evidence was found to support a previous suggestion (Pilet and Phipps, 1968) that IAA-oxidase activity and chlorophyll levels were causally linked.