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1.
Does light inhibit ethylene production in leaves?   总被引:3,自引:1,他引:2       下载免费PDF全文
The effect of light on the rate of ethylene production was monitored using two different techniques—leaf segments incubated in closed flasks versus intact plants in a flow-through open system. Three different plants were used, viz sunflower (Helianthus annuus), tomato (Lycopersicon esculentum), and soybean (Glycine max). Experiments were conducted both in the presence and absence of 1-aminocyclopropane-1-carboxylic acid (ACC).

The results obtained indicate that, in all three species studied, light strongly inhibits ethylene production when cut leaf segments are incubated in the presence of ACC in closed flasks. When ethylene measurements are made with ACC-sprayed intact plants using a continuous flow system, the effect of light on ethylene production is only marginal. In leaf segments of sunflower and soybean incubated only in distilled H2O in closed flasks, light promotes ethylene production. In tomato, there is no difference between the rate of ethylene production between light and darkness under such conditions. When measurements are made with intact plants in a continuous flow system, the rate of ethylene production is almost identical in light and darkness, in the three plants studied.

It is concluded that the effect of light on cut leaf segments incubated in the presence of ACC in closed flasks can be attributed to the techniques used for these measurements. Light has little effect on ethylene production by intact plants in an open system.

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2.
3.
The regulatory effect of light quality on the photosynthetic apparatus in attached leaves of rice plants was investigated by keeping rice plants under natural light, in complete darkness, or under illumination with light of different colors. When leaves were left in darkness and far-red (FR)-light conditions for 6 days at 30°C, there was an initial lag in chlorophyll (Chl) content, Chl a/b ratio, and maximum photosystem (PS) II photochemistry that lasted until the second day; these then rapidly decreased on the fourth day. In contrast, ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) rapidly disappeared with no lag under low or zero light conditions. By using spectrophotometric quantitation, it was determined that the PSII and PSI reaction centers were regulated by light quality, but cytochrome (Cyt) f was regulated by light intensity. However, the PSII heterogeneity was also strongly modified by the light intensity; PSIIα with the large antenna decreased markedly both in content and in antenna size. Consequently, the PSIIα/PSI ratio declined under FR-light because the low intensity of FR-light dominated over its quality in the modulation of the PSIIα/PSI ratio. An imbalance between them induced the generation of reactive oxygen species (ROS), although the ROS were scavenged by stromal enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR). The activities of these stromal enzymes are also regulated by light quality. Thus, although the photosynthetic apparatus is regulated differently depending on light quality, light quality may play an important role in the regulation of the photosynthetic apparatus.  相似文献   

4.
We studied how plants acclimated to growing conditions that included combinations of blue light (BL) and ultraviolet (UV)‐A radiation, and whether their growing environment affected their photosynthetic capacity during and after a brief period of acute high light (as might happen during an under‐canopy sunfleck). Arabidopsis thaliana Landsberg erecta wild‐type were compared with mutants lacking functional blue light and UV photoreceptors: phototropin 1, cryptochromes (CRY1 and CRY2) and UV RESISTANT LOCUS 8 (uvr8). This was achieved using light‐emitting‐diode (LED) lamps in a controlled environment to create treatments with or without BL, in a split‐plot design with or without UV‐A radiation. We compared the accumulation of phenolic compounds under growth conditions and after exposure to 30 min of high light at the end of the experiment (46 days), and likewise measured the operational efficiency of photosystem II (?PSII, a proxy for photosynthetic performance) and dark‐adapted maximum quantum yield (Fv/Fm to assess PSII damage). Our results indicate that cryptochromes are the main photoreceptors regulating phenolic compound accumulation in response to BL and UV‐A radiation, and a lack of functional cryptochromes impairs photosynthetic performance under high light. Our findings also reveal a role for UVR8 in accumulating flavonoids in response to a low UV‐A dose. Interestingly, phototropin 1 partially mediated constitutive accumulation of phenolic compounds in the absence of BL. Low‐irradiance BL and UV‐A did not improve ?PSII and Fv/Fm upon our acute high‐light treatment; however, CRYs played an important role in ameliorating high‐light stress.  相似文献   

5.
Chlorophyll fluorescence induction curves induced by an actinic pulse of red light follow different kinetics in dark-adapted plant leaves and leaves preilluminated with far-red light. This influence of far-red light was abolished in leaves infiltrated with valinomycin known to eliminate the electrical (Δφ) component of the proton-motive force and was strongly enhanced in leaves infiltrated with nigericin that abolishes the ΔpH component. The supposed influence of ionophores on different components of the proton motive force was supported by differential effects of these ionophores on the induction curves of the millisecond component of chlorophyll delayed fluorescence. Comparison of fluorescence induction curves with the kinetics of P700 oxidation in the absence and presence of ionophores suggests that valinomycin facilitates a build-up of a rate-limiting step for electron transport at the site of plastoquinone oxidation, whereas nigericin effectively removes limitations at this site. Far-red light was found to be a particularly effective modulator of electron flows in chloroplasts in the absence of ΔpH backpressure on operation of the electron-transport chain.  相似文献   

6.
Leaf respiration continues in the light but at a reduced rate. This inhibition is highly variable, and the mechanisms are poorly known, partly due to the lack of a formal model that can generate testable hypotheses. We derived an analytical model for non‐photorespiratory CO2 release by solving steady‐state supply/demand equations for ATP, NADH and NADPH, coupled to a widely used photosynthesis model. We used this model to evaluate causes for suppression of respiration by light. The model agrees with many observations, including highly variable suppression at saturating light, greater suppression in mature leaves, reduced assimilatory quotient (ratio of net CO2 and O2 exchange) concurrent with nitrate reduction and a Kok effect (discrete change in quantum yield at low light). The model predicts engagement of non‐phosphorylating pathways at moderate to high light, or concurrent with processes that yield ATP and NADH, such as fatty acid or terpenoid synthesis. Suppression of respiration is governed largely by photosynthetic adenylate balance, although photorespiratory NADH may contribute at sub‐saturating light. Key questions include the precise diel variation of anabolism and the ATP : 2e ratio for photophosphorylation. Our model can focus experimental research and is a step towards a fully process‐based model of CO2 exchange.  相似文献   

7.
Treefall gaps in tropical forests have a profound effect on plants growing in the understory, primarily due to increased light availability. In higher light, mature leaves typically have increased anti-herbivore defenses. However, since the majority of herbivory occurs while leaves are expanding, it is important to determine whether defense expression during the short period of leaf expansion is canalized (invariant) or plastic in response to variation in light. Therefore, we examined young leaves of Inga paraensis (Fabaceae) saplings growing along a light gradient in a terra-firme forest in Central Amazonia. We quantified leaf production and expansion time, dry mass of phenolics, saponins, and nitrogen, ants attracted to extrafloral nectaries, and leaf consumption. Over the entire light gradient, the number of leaves produced per flush increased by 50?% and the mass of phenolic compounds by 20?%, but no other traits changed. On average, 39?% of leaf area was consumed with no difference across the light gradient. Alone, none of the leaf traits was a significant predictor of leaf consumption, except for phenolics, which showed a positive relationship. Multiple regressions showed that leaf consumption was positively related to more leaves per flush and a higher concentration of phenolics in leaves. Unlike studies of mature leaves, young leaves of I. paraensis show low plasticity in defense traits across a light gradient, suggesting that leaf development is canalized.  相似文献   

8.
The "saturating pulse" method of in vivo Chl fluorescence measurement has been widely used by physiologists and especially ecophysiologists, as it allows a simple, rapid and non-invasive assessment of PSII function and the allocation of absorbed energy into photochemical and non-photochemical processes. It is based on the accurate determination of the so-called Fm('), i.e. the fluorescence signal emitted when a "saturating" light pulse closes all PSII centers. In this methodological investigation, we examined whether the saturating pulse intensities required to obtain maximal fluorescence yields differ between leaves of various species receiving varying actinic light irradiances. It was shown that, in leaves adapted to comparatively high (yet realistic) levels of natural irradiances, the saturating pulses usually applied are not able to close all PSII reaction centers. As a result, there is a high risk of considerable Fm(') underestimation. Accordingly, the derived values of effective PSII yields and linear electron transport rates (ETR) are also underestimated, even at the highest saturation pulse levels afforded by commercial instruments. Since the extent of underestimation increases with actinic irradiance, the ETR versus light curves are considerably distorted. The possible reasons for the apparent inability of "saturating" pulses to close all PSII centers at high actinic light and the practical implications, especially in field work, are discussed.  相似文献   

9.
Red (retro)-carotenoids accumulate in chloroplasts of Buxus sempervirens leaves during the process of winter leaf acclimation. As a result of their irregular presence, different leaf colour phenotypes can be found simultaneously in the same location. Five different colour phenotypes (green, brown, red, orange, and yellow), with a distinct pattern of pigment distribution and concentration, have been characterized. Leaf reddening due to the presence of anthocyanins or carotenoids, is a process frequently observed in plant species under photoinhibitory situations. Two main hypotheses have been proposed to explain the function of such colour change: antioxidative protection exerted by red-coloured molecules, and green light filtering. The potential photoprotective role of red (retro-) carotenoids as light filters was tested in Buxus sempervirens leaves. In shade leaves of this species the upper (adaxial) mesophyll of the lamina was replaced by the equivalent upper part of a different colour phenotype. These hybrid leaves were exposed to a photoinhibitory treatment in order to compare the photoprotective effect exerted by adaxial parts of phenotypes with a different proportion of red (retro)-carotenoids in the lower mesophyll of a shade leaf. The results indicated that the presence of red (retro)-carotenoids in the upper mesophyll did not increase photoprotection of the lower mesophyll when compared with chlorophyll, and the best protection was achieved by an upper green layer. This was due to the fact that the extent of photoinhibition was proportional to the amount of red light transmitted by the upper mesophyll and/or to the chlorophyll pool located above. These results do not exclude a protective function of carotenoids in the upper leaf layer, but imply that, at least under the conditions of this experiment, the accumulation of red pigments in the outer leaf layers does not increase photoprotection in the lower mesophyll.  相似文献   

10.
Plant β-glucosidases catalyze the hydrolysis of glycosidic linkages and play a vital role in defense against pathogens and stress. The present work investigated the relationship between leaf development and β-glucosidase protein content in Olea europea L. (cv. Picual) leaves. The total chlorophyll content increased with leaf age in current-season leaves. Immunoblot analysis revealed that the content of 61 kD protein of β-glucosidase also increased with leaf age, and that the enzyme existed in three isoforms (pI 5.8–6.2). Statistical analysis indicated a strong correlation between chlorophyll and β-glucosidase protein contents.  相似文献   

11.
《Phytochemistry》1987,26(7):2029-2031
A rare secocarotenoid, semi-β-carotenone, has been isolated from young leaves of Ceratozamia fuscoviridis (a form of C. mexicana Brongn.) and of C. kuesteriana. This is the first time that this carotenoid has been obtained from photosynthetic tissue. New data on the chromatographic behaviour and on the spectroscopic properties of the carotenoid are presented.  相似文献   

12.
Changes in (1→3,1→4)-β-D-glucan endohydrolase (EC 3.2.1.73) protein levels were investigated in segments from second leaves of wheat (Triticum aestivum L.). The abundance of the enzyme protein markedly increased when leaf segments were incubated in the dark whereas the enzyme rapidly disappeared when dark-incubated segments were illuminated or fed with sucrose. Addition of cycloheximide (CHI) to the incubation medium led to the disappearance of previously synthesized (1→3,1→4)-β-glucanase and suppressed the dark-induced accumulation indicating that the enzyme was rather unstable. The degradation of (1→3,1→4)-β-glucanase was analyzed without the interference of de-novo synthesis in intercellular washing fluid (IWF). The loss of the enzyme protein during incubation of IWF (containing naturally present peptide hydrolases) indicated that the stability increased from pH 4 to pH 7 and that an increase in the temperature from 25 to 35 °C considerably decreased the stability. Chelating divalent cations in the IWF with o-phenanthroline also resulted in a lowered stability of the enzyme. A strong temperature effect in the range from 25 to 35 °C was also observed in wheat leaf segments. Diurnal changes in (1→3,1→4)-β-glucanase activity were followed in intact second leaves from young wheat plants. At the end of the dark period, the activity was high but constantly decreased during the light phase and remained low if the light period was extended. Activity returned to the initial level during a 10-h dark phase. During a diurnal cycle, changes in (1→3,1→4)-β-glucanase activity were associated with reciprocal changes in soluble carbohydrates. The results suggest that the synthesis and the proteolytic degradation of an apoplastic enzyme may rapidly respond to changing environmental conditions.  相似文献   

13.
The immunoglobulin λ isotype is present in nearly all vertebrates and plays an important role in the human immune system. Despite its importance, few systematic studies have been performed to analyze the structural conformation of its variable regions, contrary to what is the case for κ and heavy chains. We show here that an analysis of the structures of λ chains allows the definition of a discrete set of recurring conformations (canonical structures) of their hypervariable loops and, most importantly, the identification of sequence constraints that can be used to predict their structure. We also show that the structural repertoire of λ chains is different and more varied than that of the κ chains, consistently with the current view of the involvement of the two major light-chain families in complementary strategies of the immune system to ensure a fine tuning between diversity and stability in antigen recognition.  相似文献   

14.
Fast cyclic electron transport (CET) around photosystem I (PS I) was observed in sunflower (Helianthus annuus L.) leaves under intense far-red light (FRL) of up to 200 μmol quanta m−2 s−1. The electron transport rate (ETR) through PS I was found from the FRL-dark transmittance change at 810 and 950 nm, which was deconvoluted into redox states and pool sizes of P700, plastocyanin (PC) and cytochrome f (Cyt f). PC and P700 were in redox equilibrium with K e = 35 (ΔE m = 90 mV). PS II ETR was based on O2 evolution. CET [(PS I ETR) − (PS II ETR)] increased to 50–70 μmol e m−2 s−1 when linear electron transport (LET) under FRL was limited to 5 μmol e m−2 s−1 in a gas phase containing 20–40 μmol CO2 mol−1 and 20 μmol O2 mol−1. Under these conditions, pulse-saturated fluorescence yield F m was non-photochemically quenched; however, F m was similarly quenched when LET was driven by low green or white light, which energetically precluded the possibility for active CET. We suggest that under FRL, CET is rather not coupled to transmembrane proton translocation than the CET-coupled protons are short-circuited via proton channels regulated to open at high ΔpH. A kinetic analysis of CET electron donors and acceptors suggests the CET pathway is that of the reversed Q-cycle: Fd → (FNR) → Cyt cn → Cyt bh → Cyt bl → Rieske FeS → Cyt f → PC → P700 →→ Fd. CET is activated when PQH2 oxidation is opposed by high ΔpH, and ferredoxin (Fd) is reduced due to low availability of e acceptors. The physiological significance of CET may be photoprotective, as CET may be regarded as a mechanism of energy dissipation under stress conditions.  相似文献   

15.
Several deciduous woody plant species produce anthocyanins during leaf development in spring and again during leaf senescence in autumn. The leaves of Betula pendula Roth (silver birch) commonly exhibit transient reddening in juvenile leaves under northern growing conditions, with the intensity of the red colour varying among individual trees. The objective of our study was to test the hypothesis that the accumulation of foliar anthocyanins during spring in leaves of B. pendula is an ecotypic response. Chlorophyll fluorescence ratio (Fv/Fm), leaf reflectance and anthocyanin concentrations were measured, in relation to phenology in spring, summer and autumn from birches used for landscaping with either red or green-emergent leaves. The results suggest that (1) the trees with green- or red-emergent juvenile leaves represent different populations, and (2) that the red-emergent leaves senesced earlier, indicating that (3) trees with red-emerging leaves belong to a more northern ecotype than the trees with green-emerging leaves. The role of anthocyanin synthesis in a northern radiation environment is discussed.  相似文献   

16.
A water extract of the leaves of Suregada glomerulata (Euphorbiaceae) was found to inhibit rat small intestinal α-glucosidase. An examination of the extract afforded 20 iminosugars including one pyrrolidine and 19 piperidines. The structures of the 10 new compounds (1120) were determined by NMR, and MS spectroscopic data analyses, and chemical correlations. The novelty of the identified compounds mainly stems from the loss of a hydroxy at C-4 and the presence of an 8-hydroxyoctyl side chain. Nine N-alkyl derivatives including N-methyl (1a, 8a, and 13a), N-butyl (1b, 2b, and 9b) and N,N-dimethyl (1c, 2c, and 9c) were synthesized. The compounds were tested for rat small intestinal α-glucosidase inhibitory activity. In total, 15 compounds, including compounds 11, 12, 15, and 19 and the three derivatives 8a, 9b, and 13a, showed inhibitory activity with IC50 values less than 40 μM. In vivo results showed that total alkaloids of S. glomerulata (10 mg/kg) and four major iminosugars 1, 2, 3, and 9 (10 mg/kg) can lower the postprandial blood glucose level after sucrose and starch load in healthy male ICR mice.  相似文献   

17.
Estimation of radionuclide concentrations in trees may be required to estimate their radiation exposure. However, concentration ratios of radionuclides from soil to tree species are limited for many radionuclide-tree combinations. To fill this gap, it is investigated in the present paper whether stable element concentration data for leafy vegetables are representative of those for wild tree leaves, and consequently, if these stable element data for leafy vegetables can be used as analogues to describe radionuclides transfer from soil to trees. Data for stable elements in leafy vegetables collected in Japan were compared with those in leaves of about 20 tree species worldwide. The correlation coefficients of element concentrations between leafy vegetables and tree leaves were higher than 0.90 with p < 0.001 by Student’s t test, and geometric means of concentration data for most elements were within the range of data for leafy vegetables. Thus, transfer parameters derived from stable element data for leafy vegetables could generally be used to estimate concentrations in tree leaves if data for the latter are not available. However, some trees accumulate a few elements (e.g., Al, Co, Mn and Si) in their leaves to higher concentrations than observed for leafy vegetables.  相似文献   

18.
E. Medina  P. Minchin 《Oecologia》1980,45(3):377-378
Summary The contribution of soil respiration to the photosynthesis of the shade flora in the Amazon forest was evaluated by measuring the 13C values of leaves collected at different levels in two forest communities. Canopy leaves have an average 13C of-30.5 in the podsol forest and-28.7 in the laterite forest. Leaves from plants in the lower forest strata have a significantly lower value of-35.2 in the podsol forest and-34.3 in the laterite forest.Mailing address of the first author: Before May 31, 1980: Department of Biological Sciences, Stanford University, Stanford, California 94305 USA. After May 31: Centro de Ecologia, IVIC Aptdo. 1827. Caracas, Venezuela  相似文献   

19.
In greening maize leaves δ-aminolevulinic acid (ALA) was not formed from succinyl-CoA and glycine as shown by the incorporation of [14C]-labeled  相似文献   

20.
The non-chloroplastic -glucan phosphorylase (EC 2.4.1.1) from spinach leaves has been purified to homogeneity as revealed by dodecylsulfate gel electrophoresis. Both purification and separation from the chloroplastic phosphorylase were achieved by chromatography on Sepharose-bound dextrin. The chloroplastic phosphorylase did not bind to Sepharose-dextrin and was removed from the column by washing with buffer, as verified by polyacrylamide gel electrophoresis of the buffer eluate and by chromatography of a preparation from isolated intact chloroplasts. The non-chloroplastic phosphorylase did bind to a high extent to Sepharose-dextrin and could be eluted by a dextrin gradient. Based on dodecylsulfate gel electrophoresis and pyridoxal phosphate determination, a molecular weight of about 90,000 was found for the monomer. Molecular-weight determination by porosity density gradient electrophoresis and gel filtration on Sephadex G-200 suggested that the native enzyme is a dimer, as are other phosphorylases.Abbreviations DEAE diethylaminoethyl - EDTA ethylenediamine tetraacetic acid - G1P glucose 1-phosphate - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid - PMSF phenylmethyl sulphonyl fluoride - SDS sodium dodecylsulfate - Tris Tris (hydroxymethyl)aminomethane Dedicated to Professor Dr. A. Pirson on the occasion of his 70th birthday  相似文献   

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