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1.
The uptake of 5-[3H]indol-3yl-acetic acid (IAA*) by segments of Zea mays L. roots was measured in the presence of nonradioactive indol-3yl-acetic acid (IAA°) at different concentrations. IAA uptake was found to have a nonsaturable component and a saturable part with (at pH 5.0) an apparent Km of 0.285 micromolar and apparent Vmax 55.0 picomoles per gram fresh mass per minute. These results are consistent with those which might be expected for a saturable carrier capable of regulating IAA levels. High performance liquid chromatography analyses showed that very little metabolism of IAA* took place during 4 minute uptake experiments. Whereas nonsaturable uptake was similar for all 2 millimeter long segments prepared within the 2 to 10 millimeter region, saturable uptake was greatest for the 2 to 4 millimeter region. High levels of uptake by stelar (as compared with cortical) segments are partly attributable to the saturable carrier, and also to a high level of uptake by nonsaturable processes. The carrier may play an essential role in controlling IAA levels in maize roots, especially the accumulation of IAA in the apical region. The increase in saturable uptake toward the root tip may also contribute to the acropetal polarity of auxin transport. 相似文献
2.
The levels of free and ester-linked indole-3-acetic acid (IAA) in different parts of the maize root were measured using gas chromatography-mass spectrometry (selected ion monitoring). In roots of 2-day-old plants, the distribution of free and ester IAA differed both along the root and between stele and cortex. The levels of IAA and IAA esters were then measured in whole roots and in the elongation zone using roots of different ages. The level of ester IAA decreased steadily with time. In contrast, the level of free IAA in the elongation zone was found to increase after a few days of culture at which time the rate of root growth was decreasing. 相似文献
3.
A M Guihard-Costa 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1991,312(8):403-405
We suggest a new method to calculate fetal growth velocity. Fetal growth curves are divided in small linear units, and corresponding slopes calculated as growth rates. An example is detailed to set out statistical contingencies for methodological reliability. Specific interest of the method is discussed. 相似文献
4.
Water stress and indol-3yl-acetic acid content of maize roots 总被引:2,自引:0,他引:2
Water-stress conditions were applied to the apical 12 mm of intact or excised roots ofZea mays L. (cv. LG 11) using mannitol solutions (0 to 0.66 M) and changes in weight, water content, growth and IAA level of these
roots were investigated. With increasing stress a decrease in growth, correlated with an increased IAA level, was observed.
The largest increase in IAA (about 2.7-fold) was found in the apical 5 mm of the root and was obtained under a stress corresponding
to an osmotic potential of −1.39 MPa in the solution. This stress led to an isotonic state in the cells after 1 h. When the
duration of water stress (−1.09 MPa) was increased to 2 or 3 h, no further increase in the IAA content was observed in the
root segments. This indicated that there was no correlation between a hypothetical passive penetration of mannitol in the
cells and IAA content. Indol-3yl-acetic acid rose to the same level in excised as in intact roots. In both cases, IAA accumulation
was apparently independent of the hydrolysis of the conjugated form. The caryopsis and shoot seem not to be necessary to induce
the increase of the IAA level in the roots during water stress (−1.09 MPa). Therefore, there seems to be a high rate of IAA
biosynthesis in excised maize roots under water-stress conditions. Exodiffusion of IAA was observed during an immersion in
either buffer or stress (−1.09 MPa) solution. In both cases, this IAA efflux into the medium represented about 50% of the
endogenous level. Considering the present results, IAA appears to play an important part in the regulation of maize root metabolism
and growth under water deficiency. 相似文献
5.
Pilet PE 《Journal of plant physiology》1998,152(2-3):135-138
The graviresponsiveness of intact and primary maize roots kept horizontally in darkness and humid air is analysed. A precise local application of IAA is possible when using resin beads (diameter: 0.45 +/- 0.05 mm) loaded with IAA. The beads are placed on the upper or lower sides of the caps. They significantly change the root gravireaction. The effect of IAA is discussed in terms of its possible level in the growing and gravibending zones and its transport (acropetal, lateral and basipetal) respectively in the stele, the cap and the cortex of the elongating root. 相似文献
6.
The level of endogenous Indol-3-yl-acetic acid (IAA) measured by gas chromatography-mass spectrometry in the elongating zone of intact primary roots of Zea mays showed a good linear correlation with the growth rate of these roots. When they were treated with IAA, their relative elongation decreased; this indicates a supraoptimal content of endogenous IAA. However, the growth of some of the relatively rapidly extending roots was enhanced by such treatment. Interactions between endogenous and applied IAA in the control of root growth are discussed.Abbreviations GC-MS
gas chromatography-mass spectrometry
- IAA
Indol-3-yl-acetic acid 相似文献
7.
Ontogenetic Changes in the Transport of Indol-3yl-acetic Acid into Maize Roots from the Shoot and Caryopsis
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The quantities of endogenous indol-3yl-acetic acid (IAA) in endosperms and scutella of 6-day-old maize seedlings (Zea mays L. cv Giant White Horsetooth) were determined by a fluorimetric method. Endosperms were found to contain 33.4 nanograms IAA per plant, and scutella 7.5 nanograms IAA per plant. [5-3H]IAA applied to endosperms of 6-day-old seedlings moved into the roots and radioactivity accumulated at the apex of the primary root within 8 hours. Two to 7-day-old seedlings were treated simultaneously with [5-3H]IAA in the endosperm and [2-14C] IAA on the shoot apex. The patterns of transport into the root were found to change during ontogeny: in successively older plants, transport from the shoot into the roots increased relative to transport from the endosperm into the roots. The auxin required for the growth of maize roots could, therefore, partially be contributed by the shoot and endosperm. Ontogenetic changes in the relative importance of these two supplies could be of significance for the integration of growth and development between shoot and root. 相似文献
8.
A totally data-based approach to the evaluation of short-term tests is proposed. The performances of 22 tests over a range of 42 chemicals (data from literature) were studied by cluster analysis. The comparison between them was performed only on the basis of their responses to the chemicals. Two different clustering methods produced a coincident classification, pointing to a clear resolution of all tests into 3 groups with common characteristics. With respect to carcinogen discrimination, cluster 1 showed the highest sensitivity and the lowest specificity. Cluster 3 had opposite characteristics. The tests of cluster 2 showed intermediate features. As far as the membership to clusters is concerned, the literature data about the responses to chemicals indicated a strong test system specificity. This apparently overcame both phylogeny and end-point community. A major characteristic of the present approach is the ability to elicit underlying patterns, the knowledge of which can contribute both to hypothesis formulation and be useful for practical purposes. 相似文献
9.
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 of14C-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 of14C 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. 相似文献
10.
Endogenous, free indol-3yl-acetic acid (IAA) levels were measured in the main stem in the 10-year-old cambial zone, in the adjoining differentiating xylem, and in the adjoining mature xylem of 15–20-year-old Pinus contorta Dougl. by single-ion-current monitoring, combined gas chromatography — mass spectrometry, on several dates from early spring to early winter. Microscopy was used to determine the state of cambial activity on each harvest date. The IAA levels were found to be nearly constant at 1 g g-1 DW in the cambial zone from March to July, then to increase to near 2 g g-1 DW during the remainder of the growth season. No clear correlation was evident between number of fusiform cells per radial file and IAA content in the cambial zone. By contrast, the IAA content in differentiating xylem was higher than that in the adjoining meristematic zone on all harvest dates and also exhibited marked seasonal variation, peaking near 16 g g-1 DW in mid summer, and declining to 1 g g-1 DW in autumn. In mature xylem, IAA levels were very low and showed negligible variation. The fresh weight to dry weight ratio of differentiating xylem was greater than that of the cambial zone, and greater in the cambial zone than in mature xylem. 相似文献
11.
J. RAA 《Physiologia plantarum》1971,24(3):498-505
Plots of reaction rate versus substrate concentration of the enzymatic decarboxylation of IAA yield sigmoid, rather than the usual, hyperbolic curves, suggesting that the IAA oxidase of cabbage roots is an allosteric enzyme. The quantity of this enzyme in roots is so high that the IAA concentration is likely to limit IAA degradation in intact cells. Thus, variations in the level of this enzyme seem not to be essential for the regulation of the endogenous IAA concentration. Cabbage roots contain substances that can inhibit IAA oxidase. These substances are spatially separated from IAA oxidase in intact cells, but the same inhibitors are able to reach the enzyme when added exogenously to tissue segments. The possibility that added IAA is treated by tissue segments in another manner than endogenous IAA is discussed. 相似文献
12.
13.
14.
Levels of Indol-3yl-acetic Acid and Acid Inhibitors in Green and Etiolated Bean Seedlings (Phaseolus vulgaris) 总被引:1,自引:0,他引:1
ELISABETH TILLBERG 《Physiologia plantarum》1974,31(2):106-111
Indol-3yl-acetic acid (IAA) was identified in Phaseolus vulgaris L. Shoot tissue of seedlings, exposed to light for 5 days, had a higher level of IAA than etiolated seedlings of the same age. The content of IAA increased in green seedlings during light treatment for 5–12 days. No increase could be measured in dark-grown seedlings. Inhibitory substances appeared at different Rf-values. The main part was identical to the inhibitor-β complex and occurred in a higher amount in light-grown seedlings than in etiolated taller ones. One part of the inhibitor-complex appeared to be abscisic acid (ABA). It is suggested that both IAA and acid inhibitors may play an important role in the control of stem growth and differentiation, although light effects on other hormones and regulatory systems cannot be ignored. 相似文献
15.
Distal applications of indol-3yl-acetic acid (IAA) to debladed cotyledonary petioles of cotton (Gossypium hirsutum L.) seedlings greatly delayed petiole abscission, but similar applications of phenylacetic acid (PAA) slightly accelerated abscission compared with untreated controls. Both compounds prevented abscission for at least 91 h when applied directly to the abscission zone at the base of the petiole. The contrasting effects of distal IAA and PAA on abscission were correlated with their polar transport behaviour-[1-14C]IAA underwent typical polar (basipetal) transport through isolated 30 mm petiole segments, but only a weak diffusive movement of [1-14C]PAA occurred.Removal of the shoot tip substantially delayed abscission of subtending debladed cotyledonary petioles. The promotive effect of the shoot tip on petiole abscission could be replaced in decapitated shoots by applications of either IAA or PAA to the cut surface of the stem. Following the application of [1-14C]IAA or [1-14C]PAA to the cut surface of decapitated shoots, only IAA was transported basipetally through the stem. Proximal applications of either compound stimulated the acropetal transport of [14C]sucrose applied to a subtending intact cotyledonary leaf and caused label to accumulate at the shoot tip. However, PAA was considerably less active than IAA in this response.It is concluded that whilst the inhibition of petiole abscission by distal auxin is mediated by effects of auxin in cells of the abscission zone itself, the promotion of abscission by the shoot tip (or by proximal exogenous auxin) is a remote effect which does not require basipetal auxin transport to the abscission zone. Possible mechanisms to explain this indirect effect of proximal auxin on abscission are discussed. 相似文献
16.
Mass spectra of the derivatives of indol-3yl-acetic acid and cis-abscisic acid were obtained in electron impact and chemical ionization positive ion and negative ion modes. The respective merits of methane, isobutane, and ammonia as reagent gases for structure determination and sensitive detection were compared using the methyl esters. From one to 10 fluorine atoms were attached to IAA to improve the electron-capturing properties of the molecule. The best qualitative information was obtained when using positive ion chemical ionization with methane. However, the most sensitive detection, with at least two ions per molecule, was achieved by electron impact on the IAA-HFB-ME derivative and by negative ion chemical ionization with NH3 on the ABA-methyl ester derivative. p ]Quantitative analyses of ABA in different parts of maize (Zea mays cv. LG 11) root tips were performed by the latter technique. It was found that the cap and apex contained less ABA than the physiologically older parts of the root such as the elongation zone and the more differentiated tissues. This technique was also used to show a relation between maize root growth and the endogenous ABA level of the elongation zone and root tip: there is more ABA in the slowly growing roots than in the rapidly growing ones. 相似文献
17.
Background and aims
Root elongation is essential in the determination of the root system architecture (RSA). Using experimental data, we show how it varies in the RSA and suggest a new and simple modeling approach to predict these variations.Methods
We analyzed variation in elongation on data from pot-grown plants belonging to two different species (Helianthus annuus L. and Noccaea caerulescens (J.Presl & C.Presl) F.K.Mey). A stochastic model was designed with two successive steps to quantify and simulate these variations. The first step is the definition of a growth potential, reflected by the apical diameter, and depending on the size of the mother root. The second step, during elongation, describes the dynamic evolution of the meristem and its interaction with soil constraints.Results
The species exhibited differences in their structured variations and very large residual (pseudo-random) variability in elongation rate and final length. The two-step model allowed us to summarize these species characteristics, and to show the interest of considering the stochastic aspects of root growth to correctly simulate the RSA.Conclusions
Apart from being a more realistic way of simulating root development, this type of model raises new questions regarding the representation of root soil interactions during elongation. 相似文献18.
David J. James 《Physiologia plantarum》1983,57(1):154-158
During the auxin-sensitive phase of root initiation, rates of 3-indolyl- [2-14 C] acetic acid (IAA) uptake into the 1 cm bases of shoots of the apple rootstock M.9 ( Malus pumila Mill.) 'in vitro' were not significantly affected by the presence of 10−3 M phloroglucinol (PG) using either liquid or agar-solidified media. The use of a liquid medium did however reduce rates of uptake over a 10-day period of auxin application. The distribution of labelled IAA between the 1-cm base and the shoot remainder was not affected by PG.
Exposure of shoots of the difficult-to-root M.9 and the easy-to-root M.26, to 2.8 × 10−5 M IAA containing [2-14 C] IAA revealed no positive correlation between the amount of label taken up by the 1-cm base and rooting performance. M.9 bases absorbed almost twice as much label as M.26 after 9 days but had produced only one-third as many roots. Measurements of label distribution between the 1-cm base and the shoot remainder showed that less than 10% of the label moved to the shoot remainder over a 6-day period of auxin application. Dose-response curves of IAA and rooting over the range 1 × 10−5 M and 3 × 10−3 M showed that root number in M.9 was at an optimum at 1 × 10−3 M IAA after 6 days whilst M.26 required only 1 × 10−4 M for a similar response. These data support the hypothesis that differences in rooting of the two rootstocks reflect differences in the endogenous metabolism of exogenous IAA and not differences in its rates of uptake or distribution in the shoots. 相似文献
Exposure of shoots of the difficult-to-root M.9 and the easy-to-root M.26, to 2.8 × 10
19.
20.
Barley and tomato shoots were examined quantitatively for naturally-occurringindole compounds. Both tissues were found to contain detectablelevels of indol-3yl-acetic acid (IAA), indol-3yl-aldehyde, tryptamine,5-hydroxytryptamine and malonyltryptophan. Tomato shoots alsocontained small amounts of indol-3yl-lactic acid and tryptophol.These two compounds were absent in barley, but this tissue containedsignificant quantities of 3 -aminomethylindole, 3-methylaminomethylindole,gramine, N-methyltryptamine and 5-hydroxy-N-methyltryptamine.The possible importance of these compounds in the biosynthesisof IAA, or in the formation of alkaloids, is discussed. 相似文献