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1.
To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending
on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 μmol m−2 s−1) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a
control coefficient of PRK for CO2 assimilation of 0.25 at and above 800 μmol m−2 s−1. The flux control coefficient of PRK for steady-state CO2 assimilation was zero, however, at all irradiances in plant material grown at 800 μmol m−2 s−1 and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300–1600 μmol m−2 s−1). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite
content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase
and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 μmol m−2 s−1 or in the glasshouse than in plants grown at 330 μmol m−2 s−1. Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar
under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 μmol m−2 s−1 can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate.
This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase
and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate.
This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast.
Received: 15 November 1999 / Accepted: 27 January 2000 相似文献
2.
Chloroplast-avoidance response induced by high-fluence blue light in prothallial cells of the fern adiantum capillus-veneris as analyzed by microbeam irradiation 总被引:3,自引:0,他引:3
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Chloroplast movement was induced by partial cell illumination using a high-fluence blue microbeam in light-grown and dark-adapted prothallial cells of the fern Adiantum capillus-veneris. Chloroplasts inside the illuminated area moved out (high-fluence response [HFR]), whereas those outside moved toward the irradiated area (low-fluence response [LFR]), although they stopped moving when they reached the border. These results indicate that both HFR and LFR signals are generated by high-fluence blue light of the same area, and that an LFR signal can be transferred long-distance from the beam spot, although an HFR signal cannot. The lifetime of the HFR signal was calculated from the traces of chloroplast movement induced by a brief pulse from a high-fluence blue microbeam to be about 6 min. This is very short compared with that of the LFR (30–40 min; T. Kagawa, M. Wada [1994] J Plant Res 107: 389–398). These data indicate that the signal transduction pathways of the HFR and the LFR must be distinct. 相似文献
3.
Regulation by irradiance level of the mechanism for dissolved inorganic carbon (DIC) acquisition was examined in the red
macroalga Gracilaria tenuistipitata Zhang et Xia. For this purpose, affinity for external DIC, carbonic anhydrase (CA; EC 4.2.1.1) activity and content of ribulose-1,5-bisphosphate
carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were determined in thalli grown at 45 and 500 μmol photons m−2 s−1. Oxygen evolution rates declined by 50% when the medium pH was changed from 8.1 to 8.7, and the pH compensation point attained
was ca. 9.2. These characteristics were unaffected by the light treatments. In contrast, photosynthetic conductance for DIC
at pH 8.7 was doubled in thalli grown at high irradiance compared with those grown at low irradiance (to 0.74 × 10−6 from 0.33 × 10−6 m s−1). Photosynthetic rates at saturating DIC concentration were also higher by 60% in thalli grown at high irradiance. These
differences could not be attributed to changes in the use of external DIC, since external CA activity did not vary. Although
the irradiance level did not modify the pool size of Rubisco, Rubisco content expressed on a chlorophyll a basis was almost doubled at high irradiance. These results likely indicate that the internal transport of DIC towards the
active-site of Rubisco, rather than the external use of DIC, is enhanced in the thalli grown at high irradiance.
Received: 7 June 1999 / Accepted: 16 October 1999 相似文献
4.
Chloroplast photorelocation movement is important for plants to perform efficient photosynthesis. Phototropins were identified
as blue-light receptors for chloroplast movement in Arabidopsis thaliana and in the fern Adiantum capillus-veneris, whereas neochrome functions as a dual red/blue light receptor in the latter. However, the signal transduction pathways involved
in chloroplast movement remain to be clarified. To investigate the kinetic properties of signalling from these photoreceptors
to the chloroplasts, we deduced the speed of signal transfer using Adiantum capillus-veneris gametophytes. When a region of dark-adapted gametophyte cells was subjected to microbeam irradiation, chloroplasts moved
towards the irradiated area even in subsequent darkness. We therefore recorded the movement and calculated the speeds of signal
transfer by time-lapse imaging. Movement speeds under red or blue light were similar, e.g., about 1.0 μm min−1 in prothallial cells. However, speeds varied according to cell polarity in protonemal cells. The speed of signal transfer
from the protonemal apex to the base was approximately 0.7 μm min−1, but roughly 2.3 μm min−1 in the opposite direction. The speed of signal transfer in Arabidopsis thaliana mesophyll cells was approximately 0.8 μm min−1 by comparison. Surprisingly, chloroplasts located farthest away from the microbeam were found to move faster than those in
close proximity to the site of irradiation both in Adiantum capillus-veneris and A. thaliana. 相似文献
5.
Light response characteristics of a morphologically diverse group of southern hemisphere conifers as measured by chlorophyll fluorescence 总被引:5,自引:0,他引:5
Unlike northern hemisphere conifer families, the southern family, Podocarpaceae, produces a great variety of foliage forms
ranging from functionally broad-, to needle-leaved. The production of broad photosynthetic surfaces in podocarps has been
linked qualitatively to low-light-environments, and we undertook to assess the validity of this assumption by measuring the
light response of a morphologically diverse group of podocarps. The light response, as apparent photochemical electron transport
rate (ETR), was measured by modulated fluorescence in ten species of this family and six associated species (including five
Cupressaceae and one functionally needle-leaved angiosperm) all grown under identical glasshouse conditions. In all species,
ETR was found to increase as light intensity increased, reaching a peak value (ETRmax) at saturating quantum flux (PPFDsat), and decreasing thereafter. ETRmax ranged from 217 μmol electrons · m−2 · s−1 at a PPFDsat of 1725 μmol photons · m−2 · s−1 in Actinostrobus acuminatus to an ETR of 60 μmol electrons · m−2 · s−1 at a PPFDsat of 745 μmol electrons · m−2 · s−1 in Podocarpus dispermis. Good correlations were observed between ETRmax and both PPFDsat and maximum assimilation rate measured by gas-exchange analysis. The effective quantum yield at light saturation remained
constant in all species with an average value of 0.278 ± 0.0035 determined for all 16 species. Differences in the shapes of
light response curves were related to differences in the response of non-photochemical quenching (q
n), with q
n saturating faster in species with low PPFDsat. Amongst the species of Podocarpaceae, the log of average shoot width was well correlated with PPFDsat, wider leaves saturating at lower light intensities. This suggests that broadly flattened shoots in the Podocarpaceae are
an adaptation to low light intensity.
Received: 15 April 1996 / Accepted: 30 September 1996 相似文献
6.
Phototropism of rice (Oryza sativa L.) coleoptiles induced by unilateral blue light was characterized using red-light-grown seedlings. Phototropic fluence-response
relationships, investigated mainly with submerged coleoptiles, revealed three response types previously identified in oat
and maize coleoptiles: two pulse-induced positive phototropisms and a phototropism that depended on stimulation time. The
effective ranges of fluences and fluence rates were comparable to those reported for maize. Compared with oats and maize,
however, curvature responses in rice were much smaller and coleoptiles straightened faster after establishing the maximal
curvature. When stimulated continuously, submerged coleoptiles developed curvature slowly over a period of 6 h, whereas air-grown
coleoptiles, which showed smaller phototropic responsiveness, established a photogravitropic equilibrium from about 4 h of
stimulation. The plot of the equilibrium angle against log fluence rates yielded a bell-shaped optimum curve that spanned
over a relatively wide fluence-rate range; a maximal curvature of 25° occurred at a fluence rate of 1 μmol · m−2 · s−1. This optimum curve apparently reflects the light sensitivity of the steady-state phototropic response.
Received: 28 June 1996 / Accepted: 30 July 1996 相似文献
7.
Atomic force microscopy (AFM) enables the topographical structure of cells and biological materials to be resolved under
natural (physiological) conditions, without fixation and dehydration artefacts associated with imaging methods in vacuo. It
also provides a means of measuring interaction forces and the mechanical properties of biomaterials. In the present study,
AFM has been applied for the first time to the study of the mechanical properties of a natural adhesive produced by a green
plant cell. Swimming spores of the green alga Enteromorpha linza (L.) J. Ag. (7–10 μm) secrete an adhesive glycoprotein which provides firm anchorage to the substratum. Imaging of the adhesive in its
hydrated state revealed a swollen gel-like pad, approximately 1 μm thick, surrounding the spore body. Force measurements revealed
that freshly released adhesive has an adhesion strength of 173 ± 1.7 mN m−1 (mean ± SE; n=90) with a maximum value for a single adhesion force curve of 458 mN m−1. The adhesive had a compressibility (equivalent to Young's modulus) of 0.54 × 106 ± 0.05 × 106 N m−2 (mean ± SE; n=30). Within minutes of release the adhesive underwent a progressive `curing' process with a 65% reduction in mean adhesive
strength within an hour of settlement, which was also reflected in a reduction in the average length of the adhesive polymer
strands (polymer extension) and a 10-fold increase in Young's modulus. Measurements on the spore surface itself revealed considerably
lower adhesion-strength values but higher polymer-extension values than the adhesive pad, which may reflect the deposition
of different polymers on this surface as a new cell wall is formed. The study demonstrates the value of AFM to the imaging
of plant cells in the absence of fixation and dehydration artefacts and to the characterisation of the mechanical properties
of plant glycoproteins that have potential utility as adhesives.
Received: 22 February 2000 / Accepted: 20 April 2000 相似文献
8.
The role of cyclic electron transport has been re-examined in leaves of C3 plants because the bioenergetics of chloroplasts (H+/e = 3 in the presence of a Q-cycle; H+/ATP = 4 of ATP synthesis) had suggested that cyclic electron flow has no function in C3 photosynthesis. After light activation of pea leaves, the dark reduction of P700 (the donor pigment of PSI) following far-red
oxidation was much accelerated. This corresponded to loss of sensitivity of P700 to oxidation by far-red light and a large
increase in the number of electrons available to reduce P700+ in the dark. At low CO2 and O2 molar ratios, far-red light was capable of decreasing the activity of photosystem II (measured as the ratio of variable to
maximal chlorophyll fluorescence, Fv/Fm) and of increasing light scattering at 535 nm and zeaxanthin synthesis, indicating formation of a transthylakoid pH gradient.
Both the light-induced increase in the number of electrons capable of reducing far-red-oxidised P700 and the decline in Fv/Fm brought about by far-red in leaves were prevented by methyl viologen. Antimycin A inhibited CO2-dependent O2 evolution of pea leaves at saturating but not under limiting light; in its presence, far-red light failed to decrease Fv/Fm. The results indicate that cyclic electron flow regulates the quantum yield of photosystem II by decreasing the intrathylakoid
pH when there is a reduction in the availability of electron acceptors at the PSI level (e.g. during drought or cold stresses).
It also provides ATP for the carbon-reduction cycle under high light. Under these conditions, the Q-cycle is not able to maintain
a H+/e ratio of 3 for ATP synthesis: we suggest that the ratio is flexible, not obligatory.
Received: 23 February 1999 / Accepted: 19 August 1999 相似文献
9.
Infiltrating detached maize (Zeamays L.) leaves with L-galactono-1,4-lactone (L-GAL) resulted in a 4-fold increase in the content of leaf ascorbate. Upon exposure to high irradiance (1000 μmol photons m−2 s−1) at 5 °C, L-GAL leaves de-epoxidized the xanthophyll-cycle pigments faster than the control leaves; the maximal ratio of de-epoxidized
xanthophyll-cycle pigments to the whole xanthophyll-cycle pool was the same in both leaf types. The elevated ascorbate content,
together with the faster violaxanthin de-epoxidation, did not affect the degree of photoinhibition and the kinetics of the
recovery from photoinhibition, assayed by monitoring the maximum quantum efficiency of photosystem II primary photochemistry
(Fv/Fm). Under the experimental conditions, the thermal energy dissipation seems to be zeaxanthin-independent since, in contrast
to the de-epoxidation, the decrease in the efficiency of excitation-energy capture by open photosystem II reaction centers (Fv′/Fm′) during the high-irradiance treatment at low temperature showed the same kinetic in both leaf types. This was also observed
for the recovery of the maximal fluorescence after stress. Furthermore, the elevated ascorbate content did not diminish the
degradation of pigments or α-tocopherol when leaves were exposed for up to 24 h to high irradiance at low temperature. Moreover,
a higher content of ascorbate appeared to increase the requirement for reduced glutathione.
Received: 20 May 1999 / Accepted: 29 October 1999 相似文献
10.
Side branch formation in the moss, Physcomitrella patens, has been shown to be light dependent with cryptochrome 1a and 1b (Ppcry1a and Ppcry1b), being the blue light receptors for
this response (Imaizumi et al. in Plant Cell 14:373, 2002). In this study, detailed photobiological analyses were performed,
which revealed that this response involves multiple photoreceptors including cryptochromes. For light induction of branches,
blue light of a fluence rate higher than 6 μmol m−2 s−1 for period longer than 3 h is required. The number of branches increased with the increase in fluence rate and in the irradiation
period. The number of branches also increased when red light was applied together with the blue light, although red light
alone had a very few effect. By partially irradiating a cell, both receptive sites for blue and red light were found to be
located around the nucleus. Further, both red and blue light determine the positions of branches being dependent upon the
vibration plane of polarized light. Red light control of branch position was nullified by simultaneous far-red light irradiation.
A blue light effect on branch position was not found in lines with disrupted phototropin genes. Thus, dichroic phytochrome
and phototropin, possibly on the plasma membrane, regulate branch position. These results indicate that at least four distinct
photoreceptor systems, namely, cryptochromes and red light receptor around or in the nucleus, dichroic phytochrome and phototropin
around the cell periphery, are involved in the light induction of side branches in the moss Physcomitrella patens. 相似文献
11.
In caulonemal filaments of the moss, Physcomitrella patens, which had been incubated in darkness, 3 s irradiation with blue light (λmax 450 nm) at fluence rates of 100 μmol m−2 s−1 and above caused a transient␣increase in cytosolic calcium ion concentration, [Ca2+]cyt, which was both intensity- and time-dependent. Measurements of [Ca2+]cyt were made using moss transformed with the cDNA for apoaequorin and reconstituting the Ca2+-dependent photoprotein aequorin in the cytosol by incubation in coelenterazine.␣In response to blue light at fluence rates
of 100–1000 μmol photons m−2 s−1, [Ca2+]cyt increased transiently from a basal level of approximately 50 nM to between 200 and 700 nM. Irradiation with red light did
not evoke any measurable change in [Ca2+]cyt. The presence of calcium in the incubating medium was not required for the increase in [Ca2+]cyt to occur. A mutant strain, gad-139, was identified which required an irradiance of only 1 s to evoke a response. The kinetics showed a delay of approximately
6 s from the beginning of illumination before the beginning of the increase in [Ca2+]cyt. The data suggest that the activation of a photoreceptor rather than the direct opening of calcium channels is involved in
this blue-light response.
Received: 4 December 1997 / Accepted: 4 May 1998 相似文献
12.
Silvia De Simone Yoshito Oka Naomi Nishioka Satoshi Tadano Yasunori Inoue 《Journal of plant research》2000,113(1):45-53
−2 . The inductive effect of 100 Jm−2 red light could be partially reversed by subsequent far-red light only one time. On the other hand, the inductive effect
of 1,000 Jm−2 red light was partially reversed by subsequent far-red light irradiation at least twice. These results indicate the involvement
of phytochrome in this response. The inductive effect of blue light was repeatedly reversed by subsequent far-red light irradiation,
suggesting that the blue-light induction was mainly mediated by phytochrome.
Received 13 August 1999/ Accepted in revised form 22 December 1999 相似文献
13.
O. V. Avercheva E. M. Bassarskaya T. V. Zhigalova Yu. A. Berkovich S. O. Smolyanina M. R. Leont’eva A. N. Erokhin 《Russian Journal of Plant Physiology》2010,57(3):382-391
Leaf mesostructure, photochemical activity, and chloroplast photophosphorylation (PP) in the fourth true leaf of 28-day-old
Chinese cabbage (Brassica chinensis L.) plants were investigated. Plants were grown under a light source based on red (650 nm) and blue (470 nm) light-emitting
diodes (LED) with red/blue photon flux ratio of 7: 1 and under illumination with high-pressure sodium lamp (HPSL) at photon
flux densities of 391 ± 24 μmol/(m2 s) (“normal irradiance”) and 107 ± 9 μmol/(m2 s) (“low irradiance”) in photosynthetically active range. At normal irradiance, the leaf area in plants grown under HPSL
was twofold higher than in LED-illuminated plants; other parameters of leaf mesostructure were little affected by spectral
quality of incident light. The lowering of growth irradiance reduced the majority of leaf mesostructure parameters in plants
grown under illumination with HPSL, whereas in LED-illuminated plants the lowered irradiance reduced only specific leaf weight
but increased the leaf thickness and dimensions of mesophyll cells and chloroplasts. The photochemical activity of isolated
chloroplasts was almost independent of growth irradiance and light spectral quality. Light quality and intensity used for
plant growing had a considerable impact on PP in chloroplasts. At normal light intensity, the highest activity of noncyclic
PP in chloroplasts was observed for plants grown under HPSL; at low light intensity the highest rates of PP were noted for
plants grown under LED. The P/2e− ratio, which characterizes the degree of PP coupling to electron transport in the chloroplast electron transport chain, showed
a similar pattern. Thus, the narrow-band spectrum of the light source had little influence on leaf mesostructure and electron
transport rates. However, this spectrum significantly affected the chloroplast PP activity. The PP patterns at low and normal
light intensities were opposite for plants grown under LED and HPSL light sources. We suppose that growing plants under LED
array at normal light intensity disturbed the chloroplast coupling system, thus preventing the effective use of light energy
for ATP synthesis. At low light intensity, chloroplast PP activity was significantly higher under LED illumination, but plant
growth was suppressed because of impaired adaptation to low light intensity. 相似文献
14.
The dye FM1-43 was used alone or in combination with measurements of the membrane capacitance (Cm) to monitor membrane changes in protoplasts from Viciafaba L. guard cells. Confocal images of protoplasts incubated with FM1-43 (10 μM) at constant ambient osmotic pressure (πo) revealed in confocal images a slow internalisation of FM1-43-labelled membrane into the cytoplasm. As a result of this process
the relative fluorescence intensity of the cell interior (fFM,i) increased with reference to the total fluorescence (fFM,t) by 7.4 × 10−4 min−1. This steady internalisation of dye suggests the occurrence of constitutive endocytosis under constant osmotic pressure.
Steady internalisation of FM1-43 labelled membrane caused a prominent staining of a ring-like structure located beneath the
plasma membrane. Abrupt elevation of πo by 200 mosmol kg−1 caused, over the first minutes of incubation, a rapid internalisation of FM1-43 fluorescence into the cytoplasm concomitant
with a decrease in cell perimeter. Within the first 5 min the cell perimeter decreased by 7.9%. Over the same time fFM,i/fFM,t increased by 0.13, reflecting internalisation of fluorescent label into the cytoplasm. Combined measurements of Cm and total fluorescence of a protoplast (fFM,p) showed that an increase in πo evoked a decrease in Cm but no change in fFM,p. This means that surface contraction of the protoplast is due to retrieval of excess membrane from the plasma membrane and
internalisation into the cytoplasm. Further inspection of confocal images revealed that protoplast shrinking was only occasionally
associated with internalisation of giant vesicles (median diameter 2.7 μm) with FM1-43-labelled membrane. But, in all cases,
osmotic contraction was correlated with a diffuse distribution of FM1-43 label throughout the cytoplasm. From this, we conclude
that endocytosis of small vesicles into the cytoplasm is the obligatory process by which cells accommodate an osmotically
driven decrease in membrane surface area.
Received: 4 May 1999 / Accepted: 19 August 1999 相似文献
15.
When there is a saturating supply of dissolved carbon available, photosynthetic energy storage efficiency (ES) varies linearly
with light fluence rate (I) for both Vallisneria americana and Pisum sativum leaves. The frequently reported hyperbolic relationship between ES and I occurs only when low levels of dissolved carbon
are present in the medium. The linear relationship has its origin in intracellular events and implies that two heat-producing
processes limit the value of ES. The rate of one process varies as I and the other varies as I2. The rates of both processes were changed after a 2 hour exposure to 400 μmol photons m−2 s−1 of red light, speeding up the process that depends linearly on I and slowing the other. Illumination for 1 hour with 100
μmol photons m−2 s−1 of blue (but not red) light moves many chloroplasts from the periclinal to the anticlinal cell walls [Inoue and Shibata (1973)
Planta 114: 341–358]. Blue light exposure of V. americana leaf sections (a) reduced the rate of oxygen evolution under light-limiting conditions by about 22%; (b) increased the value
of ES by an amount dependent on the light fluence rate; and (c) decreased the slope of (ES v I). The slope change indicated
that light absorption had fallen by 26% after blue light exposure. The rate of oxygen evolution (V) was measured under light-limiting
conditions with leaf sections in which the chloroplasts had been immobilised after blue or red light exposure. With both red
and blue-exposed leaf sections, V fell by about 50% after exposure to 1 hour of 1250 μmol photons m−2 s−1 of white light. Thus accumulation of chloroplasts on anticlinal walls did not protect the leaf from photoinactivation by
a high light fluence rate.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
Summary. A randomised, double blind, placebo-controlled study was performed giving 0.5 g · kg−1 · day−1 of undiluted alanyl-glutamine (20%) or saline in a peripheral vein during 4 hours in ICU patients (n = 20). During the infusion
period a steady state in plasma concentration was reached for alanyl-glutamine, but not for alanine, glutamine or glutamate.
On the other hand there was no accumulation of any of the amino acids, as the pre-infusion concentrations were reached within
8 hours after the end of infusion. The half-life of the dipeptide was 0.26 hours (range, 0.15–0.63 h). The distribution volume
of alanyl-glutamine was larger than the extracellular water volume, indicating a rapid hydrolysis of the dipeptide. There
was no detectable alanyl-glutamine in the urine of any of the patients. All patients had excretion of small amounts of amino
acids in urine, but the renal clearance of alanine, glutamine and glutamate were not different between the two groups. 相似文献
17.
Inactivation of DNA replication origins by the cell cycle regulator, trigonelline, in root meristems of Lactuca sativa 总被引:4,自引:0,他引:4
The effects of trigonelline (TRG) on the cell cycle in root meristems of Lactuca sativa L. were examined in the knowledge that TRG is a cell cycle regulator that causes cell arrest in G2, and prevents ligation
of replicons in S-phase. The hypothesis was tested that continuous exposure to TRG would perturb DNA replication which, in
turn, would lengthen the cell cycle and impair root elongation. Using DNA fibre autoradiography, mean replicon size was 31
and 13 μm in the TRG (3 mM) and control treatments, respectively. Trigonelline also resulted in a lengthening of both S-phase
and the cell cycle and a decrease in primary root elongation. Hence, replicon inactivation was responsible for the protracted
S-phase. Trigonelline treatment also resulted in a 1.6-fold increase in fork rate (13.8 μm h−1) compared with the control (8.4 m h−1). The faster fork rate in the larger replicons is in accord with the highly significant positive relationship already established
between fork rate and replicon size for various unrelated higher plants.
Received: 11 October 1999 / Accepted: 23 December 1999 相似文献
18.
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
19.
An action spectrum for the low-fluencerate response of chloroplast movement in protonemata of the fern Adiantum capillus-veneris L. was determined using polarized light vibrating perpendicularly to the protonema axis. The spectrum had several peaks in the blue region around 450 nm and one in the red region at 680 nm, the blue peaks being higher than the red one. The red-light action was suppressed by nonpolarized far-red light given simultaneously or alternately, whereas the bluelight action was not. Chloroplast movement was also induced by a local irradiation with a narrow beam of monochromatic light. A beam of blue light at low energy fluence rates (7.3·10-3-1.0 W m-2) caused movement of the chloroplasts to the beam area (positive response), while one at high fluence rates (10 W m-2 and higher) caused movement to outside of the beam area (negative response). A red beam caused a positive response at fluence rates up to 100 W m-2, but a negative response at very high fluence rates (230 and 470 W m-2). When a far-red beam was combined with total background irradiation with red light at fluence rates causing a low-fluence-rate response in whole cells, chloroplasts moved out of the beam area. When blue light was used as background irradiation, however, a narrow far-red beam had no effect on chloroplast distribution. These results indicate that the light-oriented movement of Adiantum chloroplasts is caused by red and blue light, mediated by phytochrome and another, unidentified photoreceptor(s), respectively. This movement depends on a local gradient of the far-red-absorbing form of phytochrome or of a photoexcited blue-light photoreceptor, and it includes positive and negative responses for both red and blue light.Abbreviations BL
blue light
- FR
far-red light
-
Pfr
far-red-absorbing form of phytochrome
-
Pr
red-absorbing form of phytochrome
- R
red light
- UV
ultraviolet 相似文献
20.
Summary Changes in the organization of cortical actin microfilaments during phytochrome-mediated and blue light-induced photoorientation of chloroplasts were investigated by rhodamine-phalloidin staining in protonemal cells of the fernAdiantum capillusveneris. Low- and high-fluence rate responses were induced by partial irradiation of individual cells with a microbeam of 20 m in width. In the low-fluence rate responses to red and blue light, a circular structure composed of microfilaments was induced on the chloroplast concentrated in the irradiated region, on the side facing the plasma membrane, as already reported in the case of the low-fluence rate response induced by polarized red or blue light. Such a structure was not observed on the chloroplasts located far from the microbeam. Time-course studies revealed that the structure was induced after the chloroplasts gathered in the illuminated region and that the structure disappeared before chloroplasts moved out of this region when the microbeam was turned off. In the high-fluence rate response to blue light, chloroplasts avoided the irradiated site but accumulated in the shaded area adjacent the edges of microbeam. The circular structure made of microfilaments was also observed on the chloroplasts gathered in the area and it showed the same behavior with respect to its appearance and disappearance during a light/dark regime as in the case of the low-fluence rate response. However, no such circular structure was observed in the high-fluence rate response to red light, in which case the chloroplasts also avoided the illuminated region but no accumulation in the adjacent areas was induced. These results indicate that the circular structure composed of microfilaments may play a role in the anchorage of the chloroplast during intracellular photo-orientation. 相似文献