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1.
Takahashi H Kamada M Yamazaki Y Fujii N Higashitani A Aizawa S Yoshizaki I Kamigaichi S Mukai C Shimazu T Fukui K 《Planta》2000,210(3):515-518
Seedlings of most cucurbitaceous plants develop a peg (protuberance caused by cell outgrowth) on the transition zone between
the hypocotyl and root. The peg is necessary for removing the seed coat after germination. In our spaceflight experiments
on the STS-95 space shuttle, Discovery, we found that cucumber (Cucumis sativus L.) seedlings grown under microgravity conditions developed two pegs symmetrically at the transition zone. Thus, cucumber
seedlings potentially develop two pegs and do not require gravity for peg formation itself, but on the ground the development
of one peg is suppressed in response to gravity. This may be considered as negative control of morphogenesis by gravity.
Received: 17 August 1999 / Accepted: 4 October 1999 相似文献
2.
When cucumber seeds are germinated horizontally, an outgrowth (peg) develops on the lower side of the transition zone between the hypocotyl and the root for pulling the cotyledons and plumule out of the seed coat. We previously suggested that gravistimulation suppresses peg formation on the upper side of the transition zone when placed in a horizontal position. In the gravistimulated transition zone, auxin and the mRNAs of auxin-inducible genes are more abundant in the lower side than in the upper side. Here, using fluorescent differential display, we identified Cucumis sativus glycine-rich protein1(CsGRP1) as a gene whose mRNA accumulated more abundantly on the upper side than on the lower side of the transition zone in response to gravistimulation. Auxin starvation increased CsGRP1 mRNA in segments of the transition zone, and inhibition of polar auxin transport with 2,3,5-triiodobenzoic acid (TIBA) prevented the asymmetric accumulation of CsGRP1 mRNA. These results suggest that gravistimulation increases not only the expression of auxin-inducible genes on the lower side of the transition zone, but also the expression of auxin-repressed genes, such as CsGRP1, on the upper side of cucumber seedlings. In the hypocotyls of 3-day-old seedlings, neither gravistimulation nor changes in auxin level influenced the accumulation of CsGRP1 mRNA. These results suggest that the transition zone responds to gravistimulation in a specific manner by an asymmetric expression of CsGRP1 gene during regulation of peg formation. 相似文献
3.
Gravity-induced modification of auxin transport and distribution for peg formation in cucumber seedlings: possible roles for CS-AUX1 and CS-PIN1 总被引:5,自引:0,他引:5
Cucurbit seedlings potentially develop a peg on each side of the transition zone between the hypocotyl and root. Seedlings grown in a horizontal position suppress the development of the peg on the upper side of the transition zone in response to gravity. It is suggested that this suppression occurs due to a reduction in auxin levels to below the threshold value. We show in this study that the free indole-3-acetic acid (IAA) content is low, while IAA conjugates are significantly more abundant in the upper side of the transition zone of gravistimulated seedlings, compared to the lower side. A transient increase in mRNA of the auxin-inducible gene, CS-IAA1, was observed in the excised transition zone. The result suggests that the transition zone is a source of auxin. Cucumber seedlings treated with auxin-transport inhibitors exhibited agravitropic growth and developed a peg on each side of the transition zone. Auxin-transport inhibitors additionally caused an increase in CS-IAA1 mRNA accumulation at the transition zone, indicating a rise in intracellular auxin concentrations due to a block of auxin efflux. To study the involvement of the auxin transport system in peg formation, we isolated the cDNAs of a putative auxin influx carrier, CS-AUX1, and putative efflux carrier, CS-PIN1, from cucumber (Cucumis sativus L.) plants. Both genes (CS-AUX1 in particular) were auxin-inducible. Accumulation of CS-AUX1 and CS-PIN1 mRNAs was observed in vascular tissue, cortex and epidermis of the transition zone. A reduced level of CS-AUX1 mRNA was observed in the upper side of the gravistimulated transition zone, compared with the lower side. It is therefore possible that a balance in the activities of auxin influx and efflux carriers controls intracellular auxin concentration at the transition zone, which results in lateral placement of a peg in cucumber seedlings.Abbreviations HFCA 9-hydroxyfluorene-9-carboxylic acid - IAA indole-3-acetic acid - NPA 1-N-naphthylphthalamic acid - TIBA 2,3,5-triiodobenzoic acid 相似文献
4.
Inhibitors of the carrier-mediated influx of auxin in suspension-cultured tobacco cells 总被引:6,自引:0,他引:6
Active auxin transport in plant cells is catalyzed by two carriers working in opposite directions at the plasma membrane,
the influx and efflux carriers. A role for the efflux carrier in polar auxin transport (PAT) in plants has been shown from
studies using phytotropins. Phytotropins have been invaluable in demonstrating that PAT is essential to ensure polarized and
coordinated growth and to provide plants with the capacity to respond to environmental stimuli. However, the function of the
influx carrier at the whole-plant level is unknown. Our work aims to identify new auxin-transport inhibitors which could be
employed to investigate its function. Thirty-five aryl and aryloxyalkylcarboxylic acids were assayed for their ability to
perturb the accumulation of 2,4-dichlorophenoxyacetic acid (2,4-D) and naphthalene-1-acetic acid (1-NAA) in suspension-cultured
tobacco (Nicotiana tabacum L.) cells. As 2,4-D and 1-NAA are preferentially transported by the influx and efflux carriers, respectively, accumulation
experiments utilizing synthetic auxins provide independant information on the activities of both carriers. The majority (60%)
of compounds half-inhibited the carrier-mediated influx of [14C]2,4-D at concentrations of less than 10 μM. Most failed to interfere with [3H]NAA efflux, at least in the short term. Even though they increasingly perturbed auxin efflux when given a prolonged treatment,
several compounds were much better at discriminating between influx and efflux carrier activities than naphthalene-2-acetic
acid which is commonly employed to investigate influx-carrier properties. Structure-activity relationships and factors influencing
ligand specificity with regard to auxin carriers are discussed.
Received: 28 June 1999 / Accepted: 28 August 1999 相似文献
5.
Hideyuki Takahashi Hidetoshi Mizuno Motoshi Kamada Nobuharu Fujii Atsushi Higashitani Shigeki Kamigaichi Sachiko Aizawa Chiaki Mukai Toru Shimazu Keiji Fukui Masamichi Yamashita 《Journal of plant research》1999,112(4):497-505
peg , on the transition zone between hypocotyl and root. Our spaceflight experiment verified that the lateral positioning of a
peg in cucumber seedlings is modified by gravity. It has been suggested that auxin plays an important role in the gravity-controlled
positioning of a peg on the ground. Furthermore, cucumber seedlings grown in microgravity developed a number of the lateral
roots that grew towards the water-containing substrate in the culture vessel, whereas on the ground they oriented perpendicular
to the primary root growing down. The response of the lateral roots in microgravity was successfully mimicked by clinorotation
of cucumber seedlings on the three dimensional clinostat. However, this bending response of the lateral roots was observed
only in an aeroponic culture of the seedlings but not in solid medium. We considered the response of the lateral roots in
microgravity and on clinostat as positive hydrotropism that could easily be interfered by gravitropism on the ground. This
system with cucumber seedlings is thus a useful model of spaceflight experiment for the study of the gravimorphogenesis, root
hydrotropism and their interaction.
Received 13 September 1999/ Accepted in revised form 12 October 1999 相似文献
6.
The metabolic responses occurring in cucumber (Cucumis sativus L.) roots (a strategy-I plant) grown under iron-deficiency conditions were studied in-vivo using 31P-nuclear magnetic resonance spectroscopy. Iron starvation induced activation of metabolism leading to the consumption of
stored carbohydrates to produce the NAD(P)H, ATP and phosphoenolpyruvate necessary to sustain the increased activity of the
NAD(P)H:Fe3+-reductase, the H+-ATPase (EC 3.6.1.35) and phosphoenolpyruvate carboxylase (EC 4.1.1.31). Activation of catabolic pathways was supported by
the enhancement of glycolytic enzymes and concentrations of the metabolites glucose-6-phosphate and fructose-6-phosphate,
and by enhancement of the respiration rate. Moreover, Fe-deficiency induced a slight increase in the cytoplasmic (pHc) and vacuolar (pHv) pHs as well as a dramatic decrease in the vacuolar phosphate (Pi) concentration. A comparison was done using fusicoccin
(FC), a fungal toxin which stimulates proton extrusion. Changes in pHc and pHv were measured after addition of FC. Under these conditions, a dramatic alkalinization of the pHv of −Fe roots was observed, as well as a concomitant Pi movement from the vacuole to the cytoplasm. These results showed that
Fe starvation was indeed accompanied by the activation of metabolic processes useful for sustaining the typical responses
occurring at the plasma-membrane level (i.e. increases in the NAD(P)H:Fe3+-reductase and H+-ATPase activities) as well as those involved in the homeostasis of pHc. The decrease in vacuolar Pi levels induced by Fe-deficiency and FC and movement of Pi from the vacuole to the cytoplasm
suggest a possible involvement of this compound in the cellular pH-stat system.
Received: 30 July 1999 / Accepted: 11 November 1999 相似文献
7.
Seeds of Cichorium intybus L. var. foliosum cv. Flash were sown in acid-washed vermiculite and grown in a controlled-environment growth chamber. After 1 month of growth,
plantlets did not contain sucrose:sucrose 1-fructosyltransferase (1-SST), the key enzyme in fructan biosynthesis. No fructan
could be observed. Some of the plants were submitted to drought for 2 weeks. Glucose, fructose and sucrose concentrations
increased in roots and leaves of stressed plants and the fructan concentration in roots and leaves was ten times higher than
in control plants. The onset of fructan synthesis coincided with the increase in 1-SST activity in roots. Expression of the
1-SST gene could be observed in roots and leaves of stressed plants.
Received: 12 July 1999 / Accepted: 16 October 1999 相似文献
8.
The 1-N-naphthylphthalamic acid (NPA)-binding protein is a putative negative regulator of polar auxin transport that has been shown
to block auxin efflux from both whole plant tissues and microsomal membrane vesicles. We previously showed that NPA is hydrolyzed
by plasma-membrane amidohydrolases that co-localize with tyrosine, proline, and tryptophan-specific aminopeptidases (APs)
in the cotyledonary node, hypocotyl-root transition zone and root distal elongation zone of Arabidopsisthaliana (L.) Heynh. seedlings. Moreover, amino acyl-β-naphthylamide (aa-NA) conjugates resembling NPA in structure have NPA-like
inhibitory activity on growth, suggesting a possible role of APs in NPA action. Here we report that the same aa-NA conjugates
and the AP inhibitor bestatin also block auxin efflux from seedling tissue. Bestatin and, to a lesser extent, some aa-NA conjugates
were more effective inhibitors of low-affinity specific [3H]NPA-binding than were the flavonoids quercetin and kaempferol but had no effect on high-affinity binding. Since the APs
are inhibited by flavonoids, we compared the localization of endogenous flavonoids and APs in seedling tissue. A correlation
between AP and flavonoid localization was found in 5- to 6-d-old seedlings. Evidence that these flavonoids regulate auxin
accumulation in vivo was obtained using the flavonoid-deficient mutant, tt4. In whole-seedling [14C]indole-3-acetic acid transport studies, the pattern of auxin distribution in the tt4 mutant was shown to be altered. The defect appeared to be in auxin accumulation, as a considerable amount of auxin escaped
from the roots. Treatment of the tt4 mutant with the missing intermediate naringenin restored normal auxin distribution and accumulation by the root. These results
implicate APs and endogenous flavonoids in the regulation of auxin efflux.
Received: 2 December 1999 / Accepted: 16 January 2000 相似文献
9.
Expression of cucumber lipid-body lipoxygenase in transgenic tobacco: lipid-body lipoxygenase is correctly targeted to seed lipid bodies 总被引:2,自引:0,他引:2
A particular isoform of lipoxygenase (LOX, EC 1.13.11.12) localized on lipid bodies has been shown by earlier investigations
to play a role during seed germination in initiating the mobilization of triacylglycerols. On lipid bodies of germinating
cucumber (Cucumis sativus L.) seedlings, the modification of linoleoyl moieties by this LOX precedes the hydrolysis of the ester bonds. We analyzed
the expression and intracellular location of this particular LOX form in leaves and seeds of tobacco (Nicotiana tabacum L.) transformed with one construct coding for cucumber lipid-body LOX and one construct coding for cucumber LOX fused with
a hemagglutinin epitope. In both tissues, the amount of lipid-body LOX was clearly detectable. Biochemical analysis revealed
that in mature seeds the foreign LOX was targeted to lipid bodies, and the preferred location of the LOX on lipid bodies was
verified by immunofluorescence microscopy. Cells of the endosperm and of the embryo exhibited fluorescence based on the immunodecoration
of LOX protein whereas very weak fluorescent label was visible in seeds of untransformed control plants. Further cytochemical
analysis of transformed plants showed that the LOX protein accumulated in the cytoplasm when green leaves lacking lipid bodies
were analyzed. Increased LOX activity was shown in young leaves of transformed plants by an increase in the amounts of endogenous
(2E)-hexenal and jasmonic acid.
Received: 9 August 1999 / Accepted: 28 September 1999 相似文献
10.
Sugar regulates a variety of genes and controls plant growth and development similarly to phytohormones. As part of a screen for Arabidopsis mutants with defects in sugar-responsive gene expression, we identified a loss-of-function mutation in the HOOKLESS1 (HLS1) gene. HLS1 was originally identified to regulate apical hook formation of dark-grown seedlings (Lehman et al., 1996, Cell 85: 183-194). In hls1, sugar-induced gene expression in excised leaf petioles was more sensitive to exogenous sucrose than that in the wild type. Exogenous IAA partially repressed sugar-induced gene expression and concomitantly activated some auxin response genes such as AUR3 encoding GH3-like protein. The repression and the induction of gene expression by auxin were attenuated and enhanced, respectively, by the hls1 mutation. These results suggest that HLS1 plays a negative role in sugar and auxin signaling. Because AUR3 GH3-like protein conjugates free IAA to amino acids (Staswick et al., 2002, Plant Cell 14: 1405-1415; Staswick et al., 2005, Plant Cell 17: 616-627), enhanced expression of GH3-like genes would result in a decrease in the free IAA level. Indeed, hls1 leaves accumulated a reduced level of free IAA, suggesting that HLS1 may be involved in negative feedback regulation of IAA homeostasis through the control of GH3-like genes. We discuss the possible mechanisms by which HLS1 is involved in auxin signaling for sugar- and auxin-responsive gene expression and in IAA homeostasis. 相似文献
11.
Gravity-controlled transport of auxin was studied for a negative gravitropic response in the early growth stage of etiolated pea (Pisum sativum L. cv. Alaska) seedlings, in which epicotyl bending was observed near the cotyledon nodes of the seedlings grown continuously from seeds germinated in a horizontal or an inclined position. Increased expression of an auxin-inducible gene, PsIAA4/5, was observed in the elongated side of epicotyls grown in a horizontal or an inclined position. Regardless of the conditions of seed germination, polar auxin transport in the proximal side of the first internodes of the seedlings was significantly higher than in the distal side. Polar auxin transport in the proximal side of epicotyls grown in an inclined position was significantly lower than in those grown in a horizontal position. In contrast, lateral auxin distribution from the proximal to distal sides in epicotyls grown in an inclined position was significantly higher than in epicotyls grown in a horizontal position. Accumulation of PsPIN1 mRNA encoding a putative auxin efflux facilitator, which was observed in vascular tissue, cortex and epidermis in the proximal and distal sides of epicotyls, was markedly influenced by gravistimulation. These results strongly suggest that gravistimulation induces changeable polar auxin transport and one-way lateral auxin distribution in epicotyls as well as asymmetric auxin accumulation in the proximal and distal sides of epicotyls, resulting in a negative gravitropic response of epicotyls in the early growth stage of pea seedlings. 相似文献
12.
Summary. Taurine has been reported to enhance cholesterol 7α-hydroxylase (CYP7A1) mRNA expression in animal models. However, no in vitro studies of this effect have been reported. The Hep G2 human hepatoma cell line has been recognized as a good model for studying
the regulation of human CYP7A1. This work characterizes the effects of taurine on CYP7A1 mRNA levels of Hep G2 cells in a
dose- and time-dependent manner. In the dose-dependent experiment, Hep G2 cells were treated with 0, 2, 10 or 20 mM taurine
in the presence or absence of cholesterol 0.2 mM for 48 h. In the time-dependent experiment, Hep G2 cells were treated with
0 or 20 mM taurine for 4, 24 and 48 h with and without cholesterol 0.2 mM. Our data revealed that taurine showed time- and
dose-response effects on CYP7A1 mRNA levels in Hep G2 cells. However, glycine – a structural analogue of taurine – did not
have an effect on CYP7A1 gene expression. These results show that, in agreement to previous studies on animal models, taurine
induces the mRNA levels of CYP7A1 in Hep G2 cells, which could enhance cholesterol conversion into bile acids. Also, Hep G2
cell line may be an appropriate model to study the effects of taurine on human cholesterol metabolism. 相似文献
13.
Somatic embryogenesis induced by the simple application of abscisic acid to carrot (Daucus carota L.) seedlings in culture 总被引:3,自引:0,他引:3
Seedlings of carrot (Daucus carota L. cv. Red Cored Chantenay) formed somatic embryos when cultured on medium containing abscisic acid (ABA) as the sole source
of growth regulator. The number of embryos per number of seedlings changed depending on the concentration of ABA added to
the medium, with a maximum embryo number at 1 × 10−4 M ABA. Seedling age was critical for response to exogenous ABA; no seedling with a hypocotyl longer than 3.0 cm was able to
form an embryo. Removal of shoot apices from seedlings completely inhibited the embryogenesis induced by application of exogenous
ABA, suggesting that the action of ABA requires some substance(s) that is translocated basipetally from shoot apices through
hypocotyls. Histologically, somatic embryos shared common epidermal cells and differentiated not through the formation of
embryogenic cell clumps, but directly from epidermal cells. These morphological traits are distinct from those of embryogenesis
via formation of embryogenic cell clumps, which has been found in embryogenic carrot cultures established using 2,4-dichlorophenoxyacetic
acid or other auxins. These results suggest that ABA acts as a signal substance in stress-induced carrot seedling somatic
embryogenesis.
Received: 22 April 2000 / Accepted: 8 June 2000 相似文献
14.
Inoculation and nitrate alter phytohormone levels in soybean roots: differences between a supernodulating mutant and the wild type 总被引:9,自引:0,他引:9
The levels of different cytokinins, indole-3-acetic acid (IAA) and abscisic acid (ABA) in roots of Glycine max [L.] Merr. cv. Bragg and its supernodulating mutant nts382 were compared for the first time. Forty-eight hours after inoculation with Bradyrhizobium, quantitative and qualitative differences were found in the root's endogenous hormone status between cultivar Bragg and the
mutant nts382. The six quantified cytokinins, ranking similarly in each genotype, were present at higher concentrations (30–196% on average
for isopentenyl adenosine and dihydrozeatin riboside, respectively) in mutant roots. By contrast, the ABA content was 2-fold
higher in Bragg, while the basal levels of IAA [0.53 μmol (g DW)−1, on average] were similar in both genotypes. In 1 mM NO3
−-fed Bragg roots 48 h post-inoculation, IAA, ABA and the cytokinins isopentenyl adenine, and isopentenyl adenosine quantitatively
increased with respect to uninoculated controls. However, only the two cytokinins increased in the mutant. High NO3
− (8 mM) markedly reduced root auxin concentration, and neither genotypic differences nor the inoculation-induced increase
in auxin concentration in Bragg was observed under these conditions. Cytokinins and ABA, on the other hand, were little affected
by 8 mM NO3
−. Root IAA/cytokinin and ABA/cytokinin ratios were always higher in Bragg relative to the mutant, and responded to inoculation
(mainly in Bragg) and nitrate (both genotypes). The overall results are consistent with the auxin-burst-control hypothesis
for the explanation of autoregulation and supernodulation in soybean. However, they are still inconclusive with respect to
the inhibitory effect of NO3
−.
Received: 16 April 1999 / Accepted: 13 December 1999 相似文献
15.
The spatial pattern of acropetal and basipetal cytoplasmic streaming velocities has been studied by laser-Doppler-velocimetry
(LDV) in the positively gravitropic (downward growing) rhizoids of Chara globularis Thuill. and for the first time in the negatively gravitropic (upward growing) protonemata. The LDV method proved to be precise
and yielded reproducible results even when tiny differences in velocities were measured. In the apical parts of the streaming
regions of both cell types, acropetal streaming was faster than basipetal streaming. Starting at the apical reversal point
of streaming, the velocity increased basipetally with the distance from that point and became fairly constant close to the
basal reversal point; subsequently, the velocity decreased slightly acropetally as the apical reversal point was again approached.
There was no change in velocity at the basal reversal point. However, at the apical reversal point there was an abrupt decrease
in velocity. The pattern of the ratio of acropetal to basipetal streaming velocity (VR) was a function of the relative distance
of the site of measurement from the apical reversal point rather than a function of the absolute distance. Upon inversion
of the rhizoids, the VR decreased on average by 3.8% (±0.4%), indicating that the effect of gravity on the streaming velocity
was merely physical and without a physiological amplification. Rhizoids that had developed on the slowly rotating horizontal
axis of a clinostat, and had never experienced a constant gravity vector, were similar to normally grown rhizoids with respect
to VR pattern. In protonemata, the VR pattern was not significantly different from that in rhizoids although the direction
of growth was inverse. In rhizoids, oryzalin caused the polar organization of the cell to disappear and nullified the differences
in streaming velocities, and cytochalasin D decreased the velocity of basipetal streaming slightly more than that of acropetal
streaming. Cyclopiazonic acid, known as an inhibitor of the Ca2+-ATPase of the endoplasmic reticulum, also reduced the streaming velocities in rhizoids, but had slightly more effect on the
acropetal stream. It is possible that the endogenous difference in streaming velocities in both rhizoids and protonemata is
caused by differences in the cytoskeletal organization of the opposing streams and/or loading of inhibitors (like Ca2+) from the apical/subapical zone into the basipetally streaming endoplasm.
Received: 4 October 1999 / Accepted: 4 November 1999 相似文献
16.
It has been proposed that peg formation in the vascular transition region (TR zone) between the hypocotyl and the root in
Cucurbitaceae seedlings is a gravimorphogenetic phenomenon. Initiation of the peg became visible 36 h after imbibition when
cucumber (Cucumis sativus L. cv. Burpee Hybrid II) seeds were germinated in a horizontal position at 24°C in the dark. Simultaneously, sedimented amyloplasts
(putative statoliths) were apparent in the sheath cells surrounding the vascular strands, and in the cortical cells immediately
adjacent to them, in the TR zone. In contrast, the other cortical cells, some of which were destined to develop into the peg,
contained amyloplasts which were not sedimented. These results suggest that the graviperception mechanism for peg formation
may be like that of statoliths in shoot gravitropism. By 48 h following imbibition, the cells of the TR zone still had sedimented
amyloplasts but had lost their sensitivity to gravity, possibly because of their maturation. 相似文献
17.
18.
In this paper we examine spatio-temporal pattern formation in reaction-diffusion systems on the surface of the unit sphere
in 3D. We first generalise the usual linear stability analysis for a two-chemical system to this geometrical context. Noting
the limitations of this approach (in terms of rigorous prediction of spatially heterogeneous steady-states) leads us to develop,
as an alternative, a novel numerical method which can be applied to systems of any dimension with any reaction kinetics. This
numerical method is based on the method of lines with spherical harmonics and uses fast Fourier transforms to expedite the
computation of the reaction kinetics. Numerical experiments show that this method efficiently computes the evolution of spatial
patterns and yields numerical results which coincide with those predicted by linear stability analysis when the latter is
known. Using these tools, we then investigate the r?le that pre-pattern (Turing) theory may play in the growth and development
of solid tumours. The theoretical steady-state distributions of two chemicals (one a growth activating factor, the other a
growth inhibitory factor) are compared with the experimentally and clinically observed spatial heterogeneity of cancer cells
in small, solid spherical tumours such as multicell spheroids and carcinomas. Moreover, we suggest a number of chemicals which
are known to be produced by tumour cells (autocrine growth factors), and are also known to interact with one another, as possible
growth promoting and growth inhibiting factors respectively. In order to connect more concretely the numerical method to this
application, we compute spatially heterogeneous patterns on the surface of a growing spherical tumour, modelled as a moving-boundary
problem. The numerical results strongly support the theoretical expectations in this case. Finally in an appendix we give
a brief analysis of the numerical method.
Received: 27 July 2000 / Revised version: 15 August 2000 / Published online: 16 February 2001 相似文献
19.
20.
The tryptophan auxotroph mutant trp3-1 of Arabidopsis thaliana (L.) Heynh., despite having reduced levels of l-tryptophan, accumulates the tryptophan-derived glucosinolate, glucobrassicin and, thus, does not appear to be tryptophan-limited.
However, due to the block in tryptophan synthase, the mutant hyperaccumulates the precursor indole-3-glycerophosphate (up
to 10 mg per g FW). Instability of indole-3-glycerophosphate leads to release of indole-3-acetic acid (IAA) from this metabolite
during standard workup of samples for determination of conjugated IAA. The apparent increase in “conjugated IAA” in trp3-1 mutant plants can be traced back entirely to indole-3-glycerophosphate degradation. Thus, the levels of neither free IAA
nor conjugated IAA increase detectably in the trp3-1 mutant compared to wild-type plants. Precursor-feeding experiments to shoots of sterile-grown wild-type plants using [2H]5-l-tryptophan have shown incorporation of label from this precursor into indole-3-acetonitrile and indole-3-acetic acid with
very little isotope dilution. It is concluded that Arabidopsis thaliana shoots synthesize IAA from l-tryptophan and that the non-tryptophan pathway is probably an artifact.
Received: 1 March 2000 / Accepted: 10 April 2000 相似文献