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1.
2.
Nitrate reductase (NR) activity in spinach leaf extracts prepared in the presence of a protein phosphatase inhibitor (50 μM
cantharidine) was measured in the presence of Mg2+ (NRact) or EDTA (NRmax), under substrate saturation. These in-vitro activities were compared with nitrate reduction rates
in leaves from nitrate-sufficient plants. Spinach leaves containing up to 60 μmol nitrate per g fresh weight were illuminated
in air with their petiole in water. Their nitrate content decreased with time, permitting an estimation of nitrate reduction
in situ. The initial rates (1–2 h) of nitrate consumption were usually lower than NRact, and with longer illumination time
(4 h) the discrepancy grew even larger. When leaves were fed through their petiole with 30 mM nitrate, initial in-situ reduction
rates calculated from nitrate uptake and consumption were still lower than NRact. However, nitrate feeding through the petiole
maintained the in situ-nitrate reduction rate for a longer time. Initial rates of nitrate reduction in situ only matched NRact
when leaves were illuminated in 5% CO2. In CO2-free air or in the dark, both NRact and in-situ nitrate reduction decreased, but NRact still exceeded in-situ reduction.
More extremely, under anoxia or after feeding 5-amino-4-imidazole carboxyamide ribonucleoside in the dark, NR was activated
to the high light level; yet in spite of that, nitrate reduction in the leaf remained very low. It was examined whether the
standard assay for NRact would overestimate the in-situ rates due to a dissociation of the inactive phospho-NR-14-3-3 complex
after extraction and dilution, but no evidence for that was found. In-situ NR obviously operates below substrate saturation,
except in the light at high ambient CO2. It is suggested that in the short term (2 h), nitrate reduction in situ is mainly limited by cytosolic NADH, and cytosolic
nitrate becomes limiting only after the vacuolar nitrate pool has been partially emptied.
Received: 19 June 1999 / Accepted: 12 October 1999 相似文献
3.
The activation state of nitrate reductase is not always correlated with total nitrate reductase activity in leaves 总被引:8,自引:0,他引:8
Hui-Min Man Gaber Khallaf Abd-El Baki Petra Stegmann Hendrik Weiner Werner M. Kaiser 《Planta》1999,209(4):462-468
The relation between nitrate reductase (NR; EC 1.6.6.1) activity, activation state and NR protein in leaves of barley (Hordeum vulgare L.) seedlings was investigated. Maximum NR activity (NRAmax) and NR protein content (Western blotting) were modified by growing plants hydroponically at low (0.3 mM) or high (10 mM)
nitrate supply. In addition, plants were kept under short-day (8 h light/16 h dark) or long-day (16 h light/8 h dark) conditions
in order to manipulate the concentration of nitrate stored in the leaves during the dark phase, and the concentrations of
sugars and amino acids accumulated during the light phase, which are potential signalling compounds. Plants were also grown
under phosphate deficiency in order to modify their glucose-6-phosphate content. In high-nitrate/long-day conditions, NRAmax and NR protein were almost constant during the whole light period. Low-nitrate/long-day plants had only about 30% of the
NRAmax and NR protein of high-nitrate plants. In low-nitrate/long-day plants, NRAmax and NR protein decreased strongly during the second half of the light phase. The decrease was preceded by a strong decrease
in the leaf nitrate content. Short daylength generally led to higher nitrate concentrations in leaves. Under short-day/low-nitrate
conditions, NRAmax was slightly higher than under long-day conditions and remained almost constant during the day. This correlated with maintenance
of higher nitrate concentrations during the short light period. The NR activation state in the light was very similar in high-nitrate
and low-nitrate plants, but dark inactivation was twice as high in the high-nitrate plants. Thus, the low NRAmax in low-nitrate/long-day plants was slightly compensated by a higher activation state of NR. Such a partial compensation of
a low NRmax by a higher dark activation state was not observed with phosphate-depleted plants. Total leaf concentrations of sugars, of
glutamine and glutamate and of glucose-6-phosphate did not correlate with the NR activation state nor with NRAmax.
Received: 24 March 1999 / Accepted: 31 May 1999 相似文献
4.
This is the first report where shoot regeneration in strawberry cultivar Chandler has been achieved simultaneously through
both somatic embryogenesis and shoot bud formation. Direct somatic embryogenesis was observed in leaf discs which were cultured
on medium containing MS salts + B5 vitamins + 2% glucose + 18.16 μM thidiazuron (TDZ) and given both chilling and dark treatment for 2 wk at 4 ± 2°C followed
by incubation at 25 ± 2°C under 16-h photoperiod for third wk. After 3 wk, these explants were then subcultured on medium
containing MS salts + B5 vitamins + 2% glucose and incubated under 16-h photoperiod at 25 ± 2°C for further growth and development. Direct regeneration
via de novo shoot bud formation was observed in leaf disks which were given dark treatment and were cultured on medium containing MS
salts + B5 vitamins + 2% glucose supplemented with 9.08 μM TDZ. There was a synergistic effect of photoperiod, dark, and chilling treatments
on somatic embryogenesis, whereas chilling treatment had an inhibitory effect on shoot organogenesis. 相似文献
5.
6.
Planchet E Jagadis Gupta K Sonoda M Kaiser WM 《The Plant journal : for cell and molecular biology》2005,41(5):732-743
Quantitative data on nitric oxide (NO) production by plants, and knowledge of participating reactions and rate limiting factors are still rare. We quantified NO emission from tobacco (Nicotiana tabacum) wild-type leaves, from nitrate reductase (NR)- or nitrite reductase (NiR)-deficient leaves, from WT- or from NR-deficient cell suspensions and from mitochondria purified from leaves or cells, by following NO emission through chemiluminescence detection. In all systems, NO emission was exclusively due to the reduction of nitrite to NO, and the nitrite concentration was an important rate limiting factor. Using inhibitors and purified mitochondria, mitochondrial electron transport was identified as a major source for reduction of nitrite to NO, in addition to NR. NiR and xanthine dehydrogenase appeared to be not involved. At equal respiratory activity, mitochondria from suspension cells had a much higher capacity to produce NO than leaf mitochondria. NO emission in vivo by NiR-mutant leaves (which was not nitrite limited) was proportional to photosynthesis (high in light +CO(2), low in light -CO(2), or in the dark). With most systems including mitochondrial preparations, NO emission was low in air (and darkness for leaves), but high under anoxia (nitrogen). In contrast, NO emission by purified NR was not much different in air and nitrogen. The low aerobic NO emission of darkened leaves and cell suspensions was not due to low cytosolic NADH, and appeared only partly affected by oxygen-dependent NO scavenging. The relative contribution of NR and mitochondria to nitrite-dependent NO production is estimated. 相似文献
7.
Light modulation and in vitro effects of adenine nucleotides on leaf nitrate reductase activity in cucumber (Cucumis sativus) 总被引:1,自引:0,他引:1
Eloísa Agüera Lourdes Poblete Purificación de la Haba José M. Maldonado 《Physiologia plantarum》1999,105(2):218-223
Nitrate reductase (NR, EC 1.6.6.1) activity in attached cucumber ( Cucumis sativus L. cv. Ashley) leaves changed rapidly and reversibly during light/dark transitions, especially when assayed in the presence of free Mg2+ . Light decreased and darkness increased the sensitivity of the enzyme to inhibition by Mg2+ . The NR activation state, i.e. activity in the presence of Mg2+ relative to activity in the absence of Mg2+ , increased with light intensity up to 400 μmol m−2 s−1 PAR (photosynthetically active radiation). When a desalted crude extract from illuminated leaves was preincubated with ATP, NR was gradually inactivated. Inactivation was only observed when activity was assayed in the presence of Mg2+ . The ATP-inactivated NR remained inactive after removing the excess of ATP by gel filtration and it did not occur in partially purified NR preparations. NR extracted from darkened attached leaves was markedly activated when preincubated with 5'-AMP. These results support the view that inactivation/activation of cucumber-leaf NR in response to light/dark signals most likely involves phosphorylation/dephosphorylation of the enzyme catalysed by endogenous proteins. A substantial activation of NR by preincubation with 5'-AMP was also observed when activity was assayed in the absence of Mg2+ , thus indicating that 5'-AMP can directly activate NR. Irradiation of an extract from darkened leaves containing FAD promoted a partial activation of NR. This effect was observed both in the +Mg2+ and in the −Mg2+ assay, indicating that activation was caused by photoexcited flavin and did not involve dephosphorylation of the enzyme. 相似文献
8.
Leaf photosynthesis, plant growth and nitrogen allocation in rice under different irradiances 总被引:6,自引:0,他引:6
The photosynthetic rates and various components of photosynthesis including ribulose-1,5-bisphosphate carboxylase (Rubisco;
EC 4.1.1.39), chlorophyll (Chl), cytochrome (Cyt) f, and coupling factor 1 (CF1) contents, and sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity were examined in young, fully expanded leaves of rice
(Oryza sativa L.) grown hydroponically under two irradiances, namely, 1000 and 350 μmol quanta · m−2 · s−1, at three N concentrations. The light-saturated rate of photosynthesis measured at 1800 μmol · m−2 · s−1 was almost the same for a given leaf N content irrespective of growth irradiance. Similarly, Rubisco content and SPS activity
were not different for the same leaf N content between irradiance treatments. In contrast, Chl content was significantly greater
in the plants grown at 350 μmol · m−2 · s−1, whereas Cyt f and CF1 contents tended to be slightly smaller. However, these changes were not substantial, as shown by the fact that the light-limited
rate of photosynthesis measured at 350 μmol · m−2 · s−1 was the same or only a little higher in the plants grown at 350 μmol · m−2 · s−1 and that CO2-saturated photosynthesis did not differ between irradiance treatments. These results indicate that growth-irradiance-dependent
changes in N partitioning in a leaf were far from optimal with respect to N-use efficiency of photosynthesis. In spite of
the difference in growth irradiance, the relative growth rate of the whole plant did not differ between the treatments because
there was an increase in the leaf area ratio in the low-irradiance-grown plants. This increase was associated with the preferential
N-investment in leaf blades and the extremely low accumulation of starch and sucrose in leaf blades and sheaths, allowing
a more efficient use of the fixed carbon. Thus, morphogenic responses at the whole-plant level may be more important for plants
as an adaptation strategy to light environments than a response of N partitioning at the level of a single leaf.
Received: 23 February 1997 / Accepted: 8 May 1997 相似文献
9.
Replicon spacing was measured during the S-phase of the cell cycle in shoot meristems of Silene coeli-rosa L., a long-day (LD) plant, and Pharbitis nil Chois, a short-day (SD) plant to examine the hypothesis that activation of latent origins of DNA replication is a feature
of floral determination. Silene coeli-rosa was germinated and grown in SD for 28 d and then exposed to either a florally inductive combination of 7 LD + 2 SD, the last
day of which coincides with determination of the sepal and stamen whorls, or was germinated and grown in 37 non-inductive
SD. Pharbitis nil was germinated and grown in continuous light (CL) for 5 d and then given either 48 h of inductive darkness followed by 1 d
of CL, the last day of which coincides with determination of the sepal, petal and stamen whorls, or given one of two independent
non-inductive treatments: 48 h dark interrupted by red light (R) + 1 d of CL, or 8 d of CL. Following these treatments, each
batch of plants was exposed to tritiated [methyl-3H]thymidine for 30, 60, 90 or 120 min. Apical domes were dissected, nuclei lysed and prepared as fibre autoradiographs from
which replicon size was recorded. In S. coeli-rosa, replicon size was in the range 10–15 μm in SD (non-inductive) and 0–5 μm in LD (inductive) while in P. nil it was 10–15 μm in the 48 h dark interrupted by R, 5–10 μm in CL (both non-inductive) but was reduced to 0–5 μm in the 48 h
dark treatment (inductive). Therefore, the recruitment of additional initiation points for DNA replication occurred in both
a LD and a SD plant immediately before the appearance of floral organs. The data are consistent in showing that a shortening
of S-phase, which is a characteristic feature of florally determined shoot meristems for both species, is brought about by
the activation of latent origins of DNA replication.
Received: 14 May 1998 / Accepted: 20 August 1998 相似文献
10.
5-Aminoimidazole-4-carboxamide riboside activates nitrate reductase in darkened spinach and pea leaves 总被引:2,自引:0,他引:2
Nitrate reductase (NR) activity is modulated in vivo by phosphorylation (inactivation)/dephosphorylation (activation) in response to light/dark signals. The dephosphorylation of phospho-NR in vitro, catalyzed by endogenous protein phosphatases, is known to be stimulated by 5'-AMP suggesting that this metabolite may be an important regulator of the activity of NR, e.g. under anoxia. To determine whether 5'-AMP might be a regulatory metabolite in vivo, excised spinach ( Spinacia oleracea ) and pea ( Pisum sativum ) leaves were provided 5-aminoimidazole-4-carboxamide riboside (AICAR) via the transpiration stream, and the apparent phosphorylation status of NR was assessed by assay of activity in the presence of free Mg2+ . NR was activated in darkened spinach leaves in a time- and concentration-dependent manner when leaves were fed AICAR; there was also an accumulation of nitrite in treated leaves in the dark. The activation by AICAR could be blocked by several type 2A protein phosphatase inhibitors (microcystin-LR, okadaic acid and cantharidin), and was not the result of a reduction of kinase activity by lack of ATP because cellular adenylates were unaffected. It was confirmed that AICAR-P, but not AICAR, mimicked 5'-AMP in the activation of phospho-NR in vitro. Our results are consistent with the notion that AICAR is converted to the monophosphorylated derivative, which accumulates in cells and acts as a structural analog of 5'-AMP. Our results suggest that a rise in cytosolic [5'-AMP] may be sufficient to activate NR in vivo. AICAR should be a useful compound for identifying AMP-regulated processes in plant systems. 相似文献
11.
Iron limitation led to a large increase in extracellular ferricyanide (Fe[III]) reductase activity in cells of the green
alga Chlamydomonas reinhardtii Dangeard. Mass-spectrometric measurement of gas exchange indicated that ferricyanide reduction in the dark resulted in a
stimulation of respiratory CO2 production without affecting the rate of respiratory O2 consumption, consistent with the previously postulated activation of the oxidative pentose phosphate pathway in support of
Fe(III) reduction by iron-limited Chlamydomonas cells (X. Xue et al., 1998, J. Phycol. 34: 939–944). At saturating irradiance, the rate of ferricyanide reduction was stimulated
almost 3-fold, and this stimulation was inhibited by 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea. Ferricyanide reduction during
photosynthesis resulted in approximately a 50% inhibition of photosynthetic CO2 fixation at saturating irradiance, and almost 100% inhibition of CO2 fixation at sub-saturating irradiance. Photosynthesis by iron-sufficient cells was not affected by ferricyanide addition.
Addition of 250 μM ferricyanide to iron-limited cells in which photosynthesis was inhibited (either by the presence of glycolaldehyde,
or by maintaining the cells at the CO2 compensation point) resulted in a stimulation in the rate of gross photosynthetic O2 evolution. Chlorophyll a fluorescence measurements indicated a large increase in non-photochemical quenching during ferricyanide reduction in the
light; the increase in nonphotochemical quenching was abolished by the addition of nigericin. These results suggest that reduction
of extracellular ferricyanide (mediated at the plasma membrane) interacts with both photosynthesis and respiration, and that
both of these processes contribute NADPH in the light.
Received: 15 September 1999 / Accepted: 14 October 1999 相似文献
12.
The effects of light and elevated temperatures on the efficiency of energy conversion in PSII [?PSII = (Fm′−Fs)/Fm′], pigment composition and heat tolerance of shade-acclimated Alocasia macrorrhiza were investigated. Leaf discs were exposed for 3 h to high light (HL; 1600 μmol photons · m−2 · s−1) or low light (LL; 20 μmol photons · m−2 · s−1) and a series of constant temperatures ranging from 30 to 49 °C. All HL treatments led to rapid and severe decreases in ?PSII. During the 2-h recovery period (LL, 25 °C) following the HL treatments, fast and slow recovery phases could be distinguished.
Leaf discs that had experienced HL and 30 °C recovered completely while no recovery of ?PSII was seen after a 3-h exposure to HL and 45 °C. A 3-h exposure to 45 °C at LL led to a less severe decrease in ?PSII and complete recovery was accomplished after less than 1 h. Under LL conditions a temperature of 49 °C was necessary to cause
an irreversible decrease in ?PSII, followed by necrosis the next day. Streptomycin had no effect on the degree of reduction and recovery in ?PSII discs exposed to HL and 35–45 °C, but partially inhibited recovery in discs exposed to HL and 30 °C. Streptomycin led to
a more severe decrease in ?PSII at LL and 49 °C and completely inhibited recovery. Streptomycin had no effect on the conversion of the xanthophyll-cycle
pigments during the treatment or the recovery. The epoxidation state was roughly the same in all leaf discs after a 3-h HL
treatment (0.270–0.346) irrespective of the exposure temperature. The back-conversion of zeaxanthin into violaxanthin after
a 2-h recovery period was only seen in leaf discs that had been exposed to HL and 30 °C. The thermotolerance of shade A. macrorrhiza leaves of 49.0 ± 0.7 °C (determined by fluorescence) coincided with the temperature at which damage occurred in leaf discs
exposed to LL. However, under HL the critical temperature under which necrosis occurred was much lower (42 °C). The thermotolerance
of A. macrorrhiza shade leaves could be increased by a short exposure (<20 min) to slightly elevated temperatures.
Received: 11 June 1997 / Accepted: 9 September 1997 相似文献
13.
Nitrate reductase activation state in barley roots in relation to the energy and carbohydrate status 总被引:12,自引:0,他引:12
The NADH-dependent nitrate reductase (NR, EC 1.6.6.1) in roots of hydroponically grown barley seedlings was extracted, desalted
and the activity measured in buffer containing either Mg2+ (10 mM) or EDTA (5 mM). The former gives the actual NR activity (NRact) equivalent to dephospho-NR, whereas the latter gives the maximum NR capacity of the dephospho-form (NRmax). Both values together permit an estimation of the NR-phosphorylation state. Changes in NRact and NRmax were followed in response to root aeration or to shoot illumination or shoot removal, and were correlated with sugar contents
and adenylate levels. Ethanol formation was also measured in roots differing in NR activity in order to obtain information
on the relation between anaerobic alcoholic fermentation and nitrate reduction. In aerated roots, NR was highly phosphorylated
(about 80%) and largely inactive. It was partly dephosphorylated (activated) by anoxia or by cellular acidification (pH 4.8
plus propionic acid). Anaerobic activation (dephosphorylation) of NR was stronger at acidic external pH (5) than at slightly
alkaline pH (8), although ATP levels decreased and AMP levels increased at pH 5 and at pH 8 to the same extent. Thus, rapid
changes in the NR-phosphorylation state in response to anaerobiosis were not directly triggered by the adenylate pool, but
rather by cytosolic pH. Under prolonged darkness (24 h) or after shoot removal, NRmax decreased slowly without a large change in the phosphorylation state. This decrease of NRmax was correlated with a large decrease in the sugar content, and was prevented by glucose feeding, which had only minor effects
on the phosphorylation state. Cycloheximide also prevented the decrease in NRmax without affecting the phosphorylation state. In contrast, anaerobiosis or cellular acidification prevented the decrease of
NRmax and at the same time decreased the NR-phosphorylation state. It is suggested that NR turnover in roots is controlled by several
factors: NR synthesis appears to depend on sugar availability, which has little effect on the phosphorylation state; in addition,
NR degradation appears to be strongly affected by the phosphorylation state in such a way that the inactive phospho-NR is
a better substrate for NR degradation than the dephospho-form. The rate of anaerobic ethanol formation was not affected by
NR activity, indicating that the purpose of NR activation under hypoxia or anoxia is not to decrease or prevent alcoholic
fermentation.
Received: 29 August 1996 / Accepted: 8 November 1996 相似文献
14.
15N-labelled nitrate was used to show that nitrate reduction by leaf discs in darkness was suppressed by oxygen, whereas nitrite present within the cell could be reduced under aerobic dark conditions. In other experiments, unlabelled nitrite, allowed to accumulate in the tissue during the dark anaerobic reduction of nitrate was shown by chemical analysis to be metabolised during a subsequent dark aerobic period. Leaves of intact plants resembled incubated leaf discs in accumulating nitrite under anaerobic conditions. Nitrate, n-propanol and several respiratory inhibitors or uncouplers partly reversed the inhibitory effect of oxygen on nitrate reduction in leaf discs in the dark. Of these nitrate and propanol acted synergistically. Reversal was usually associated with inhibition of respiration but some concentrations of 2,4-dinitrophenol (DNP) and ioxynil reversed inhibition without affecting respiratory rates. Respiratory inhibitors and uncouplers stimulated nitrate reduction in the anaerobic in vivo assay i.e. in conditions where the respiratory process is non-functional. Freezing and thawing leaf discs diminished but did not eliminate the sensitivity of nitrate reduction to oxygen inhibition.Abbreviations DNP
2,4-dinitrophenol
- HOQNO
8-hydroxyquinoline-N-oxide
- DCPIP
2,6-dichlorophenolindophenol
- CCCP
Carbonyl cyanide m-chlorophenylhydrazone
- TES
N-tris(hydroxymethyl)methyl-2-amino ethanesulphonic acid
- HEPES
N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid 相似文献
15.
Effect of 1,2-benzisoxazole-3-acetic acid on adventitious shoot regeneration and in vitro rooting in apple 总被引:3,自引:0,他引:3
The effect of 1,2-benzisoxazole-3-acetic acid (BOA), compared to 1-naphthaleneacetic acid (NAA), on adventitious shoot formation
in leaf portions and compared to indolebutyric acid (IBA), on in vitro rooting in the apple (Malus domestica Borkh) cultivars McIntosh and Gala, and one rootstock, Jork 9, was investigated. BOA at 43.0 μm or 2.7 μm at NAA in combination
with 17.8 μm benzyladenine (BA), induced the highest number of explants to produce adventitious shoots in Jork 9. In Gala,
the combination of 21.5 μm BOA with 1.0 μm thidiazuron (TDZ) or with 22.0 μm BA induced the highest regeneration percentages,
58 and 54%, respectively, giving more satisfactory results than NAA (where only 42% of leaf explants exhibited shoot formation).
In McIntosh, the highest percentage of regeneration was obtained with 1.3 μm NAA and 22.0 μm BA, while 51% was the highest
response obtained with the BOA treatment. The combination of BOA with TDZ completely inhibited regeneration activity in leaf
portions of this cultivar. The shoots of all the genotypes obtained with the most morphogenetic NAA or BOA treatments were
excised, multiplied and successfully rooted and hardened. The results demonstrate that the synthetic auxin BOA is active in
inducing shoot regeneration from leaf explants of apple and that the activity of BOA in plant regeneration is genotype dependent.
When BOA was used to induce rooting in apple microcuttings, lower rooting percentages were obtained than with IBA, showing
that the effect of BOA in inducing root formation is very low and that it cannot be used routinely to replace IBA in the in
vitro rooting of microcuttings.
Received: 18 June 1998 / Revision received: 4 January 1999 / Accepted: 29 January 1999 相似文献
16.
Drought effects on photosynthesis of the mangrove, Avicennia germinans, under contrasting salinities
M. A. Sobrado 《Trees - Structure and Function》1999,13(3):125-130
Drought effects on leaf photosynthesis of A. germinans growing under two contrasting salinities were studied in a Venezuelan fringe mangrove. During both wet and dry seasons, severe
chronic-photoinhibition at predawn was not observed but strong down regulation occurred at midday during both seasons. Carbon
assimilation rates (A, μmol CO2 m−2 s−1) declined during the dry season from 11.9±1.8 to 7.0±1.5 and from 9.6±2.0 to 4.7±2.5 in plants from low and high salinity
sites, respectively. Changes in carbon assimilation per unit of chlorophyll (A/Chl, mmol CO2 mol−1 Chl) were from 31.6±4.7 to 20.5±4.3 and from 21.9±4.7 to 15.2±8.2 in the low and high salinity plants, respectively. Therefore,
neither changes in Chl nor seasonal differences in photoprotective down regulation could account fully for the decrease in
leaf photosynthesis during drought. A reduction in CO2 diffusion due to lowered stomatal conductance was not large enough to explain such a dramatic effect of drought on leaf photosynthesis.
Stomatal response could be mitigated by the capability of A. germinans for osmotic adjustment under high salinity and/or drought. However, this intracellular salt accumulation may reduce carbon
assimilation capacity further by decreasing the metabolism of leaf cells, increasing dark respiration and/or photorespiration.
Received: 10 June 1998 / Accepted: 5 October 1998 相似文献
17.
Regulation of nitric oxide (NO) production by plant nitrate reductase in vivo and in vitro. 总被引:41,自引:0,他引:41
Peter Rockel Frank Strube Andra Rockel Juergen Wildt Werner M Kaiser 《Journal of experimental botany》2002,53(366):103-110
NO (nitric oxide) production from sunflower plants (Helianthus annuus L.), detached spinach leaves (Spinacia oleracea L.), desalted spinach leaf extracts or commercial maize (Zea mays L.) leaf nitrate reductase (NR, EC 1.6.6.1) was continuously followed as NO emission into the gas phase by chemiluminescence detection, and its response to post-translational NR modulation was examined in vitro and in vivo. NR (purified or in crude extracts) in vitro produced NO at saturating NADH and nitrite concentrations at about 1% of its nitrate reduction capacity. The K(m) for nitrite was relatively high (100 microM) compared to nitrite concentrations in illuminated leaves (10 microM). NO production was competitively inhibited by physiological nitrate concentrations (K(i)=50 microM). Importantly, inactivation of NR in crude extracts by protein phosphorylation with MgATP in the presence of a protein phosphatase inhibitor also inhibited NO production. Nitrate-fertilized plants or leaves emitted NO into purified air. The NO emission was lower in the dark than in the light, but was generally only a small fraction of the total NR activity in the tissue (about 0.01-0.1%). In order to check for a modulation of NO production in vivo, NR was artificially activated by treatments such as anoxia, feeding uncouplers or AICAR (a cell permeant 5'-AMP analogue). Under all these conditions, leaves were accumulating nitrite to concentrations exceeding those in normal illuminated leaves up to 100-fold, and NO production was drastically increased especially in the dark. NO production by leaf extracts or intact leaves was unaffected by nitric oxide synthase inhibitors. It is concluded that in non-elicited leaves NO is produced in variable quantities by NR depending on the total NR activity, the NR activation state and the cytosolic nitrite and nitrate concentration. 相似文献
18.
Photosynthetic acclimation of maize to growth under elevated levels of carbon dioxide 总被引:4,自引:0,他引:4
The effects of elevated CO2 concentrations on the photochemistry, biochemistry and physiology of C4 photosynthesis were studied in maize (Zea mays L.). Plants were grown at ambient (350 μL L−1) or ca. 3 times ambient (1100 μL L−1) CO2 levels under high light conditions in a greenhouse for 30 d. Relative to plants grown at ambient CO2 levels, plants grown under elevated CO2 accumulated ca. 20% more biomass and 23% more leaf area. When measured at the CO2 concentration of growth, mature leaves of high-CO2-grown plants had higher light-saturated rates of photosynthesis (ca. 15%), lower stomatal conductance (71%), higher water-use
efficiency (225%) and higher dark respiration rates (100%). High-CO2-grown plants had lower carboxylation efficiencies (23%), measured under limiting CO2, and lower leaf protein contents (22%). Activities of a number of C3 and C4 cycle enzymes decreased on a leaf-area basis in the high-CO2-grown plants by 5–30%, with NADP-malate dehydrogenase exhibiting the greatest decrease. In contrast, activities of fructose
1,6-bisphosphatase and ADP-glucose pyrophosphorylase increased significantly under elevated CO2 condition (8% and 36%, respectively). These data show that the C4 plant maize may benefit from elevated CO2 through acclimation in the capacities of certain photosynthetic enzymes. The increased capacity to synthesize sucrose and
starch, and to utilize these end-products of photosynthesis to produce extra energy by respiration, may contribute to the
enhanced growth of maize under elevated CO2.
Received: 30 April 1999 / Accepted: 17 June 1999 相似文献
19.
Effects of hypothermic hypoxia on anaerobic energy metabolism in isolated anuran livers 总被引:1,自引:0,他引:1
C. A. Fedorow T. A. Churchill N. M. Kneteman 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(8):555-561
Many lower vertebrates (reptilian and amphibian species) are capable of surviving natural episodes of hypoxia and hypothermia.
It is by specific metabolic adaptations that anurans are able to tolerate prolonged exposure to harsh environmental stresses.
In this study, it was hypothesized that livers from an aquatic frog would possess an inherent metabolic ability to sustain
high levels of ATP in an isolated organ system, providing insight into a metabolic system that is well-adapted for low temperature
in vitro organ storage. Frogs of the species, R. pipiens were acclimated at 20 °C and at 5 °C. Livers were preserved using a clinical preservation solution after flushing. Livers
from 20 °C-acclimated frogs were stored at 20 °C and 5 °C and livers from 5 °C-acclimated frogs were stored at 5 °C. The results
indicated that hepatic adenylate status was maintained for 96 h during 5 °C storage, but not longer than 4–10 h during 20 °C
storage. In livers from 5 °C-acclimated animals subjected to 5 °C storage, ATP was maintained at 100% throughout the 96-h
period. Warm acclimation (20 °C) and 20 °C storage resulted in poorer maintenance of ATP; energy charge values dropped to
0.50 within 2 h and by 24 h, only 24% of control ATP remained. Lactate levels remained less than 25 μ mol/g dry weight in
all 5 °C-stored livers; 20 °C-stored livers exhibited greater accumulation of this anaerobic end-product (lactate reached
45–50 μ mol/g by 10 h). The data imply that hepatic adenylate status is largely dependent on exposure to hypothermic hypoxia
and although small amounts of ATP were accounted for by anaerobic glycolysis, there must have been either a substantial reduction
in cellular energy-utilization or an efficient use of low oxygen tensions.
Accepted: 24 August 1998 相似文献
20.
Gas-exchange measurements were performed to analyze the leaf conductances and assimilation rates of potato (Solanum tuberosum L. cv. Desireé) plants expressing an antisense construct against chloroplastic fructose-1,6-bisphosphatase (FBPase, EC 3.1.3.11)
in response to increasing photon flux densities, different relative air humidities and elevated CO2 concentrations. Assimilation rates (A) and transpiration rates (E) were observed during a stepwise increase of photon flux
density. These experiments were carried out under atmospheric conditions and in air containing 500 μmol mol−1 CO2. In both gas atmospheres, two levels of relative air humidity (60–70% and 70–80%) were applied in different sets of measurements.
Intercellular CO2 concentration, leaf conductance, air-to-leaf vapour pressure deficit, and instantaneous water-use efficiency (A/E) were determined.
As expected, assimilation rates of the FBPase antisense plants were significantly reduced as compared to the wild type. Saturation
of assimilation rates in transgenic plants occurred at a photon flux density of 200 μmol m−2 s−1, whereas saturation in wild type plants was observed at 600 μmol m−2 s−1. Elevated ambient CO2 levels did not effect assimilation rates of transgenic plants. At 70–80% relative humidity and atmospheric CO2 concentration the FBPase antisense plants had significantly higher leaf conductances than wild-type plants while no difference
emerged at 60–70%. These differences in leaf conductance vanished at elevated levels of ambient CO2. Stomatal response to different relative air humidities was not affected by mesophyll photosynthetic activity. It is suggested
that the regulation of stomatal opening upon changes in photon flux density is merely mediated by a signal transmitted from
mesophyll cells, whereas the intercellular CO2 concentration plays a minor role in this kind of stomatal response. The results are discussed with respect to stomatal control
by environmental parameters and mesophyll photosynthesis.
Received: 24 September 1998 / Accepted: 9 February 1999 相似文献