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1.
Comparative studies of the light modulation of nitrate reductase and sucrose-phosphate synthase activities in spinach leaves 总被引:10,自引:6,他引:4
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We recently obtained evidence that the activity of spinach (Spinacia oleracea L.) leaf nitrate reductase (NR) responds rapidly and reversibly to light/dark transitions by a mechanism that is strongly correlated with protein phosphorylation. Phosphorylation of the NR protein appears to increase sensitivity to Mg2+ inhibition, without affecting activity in the absence of Mg2+. In the present study, we have compared the light/dark modulation of sucrose-phosphate synthase (SPS), also known to be regulated by protein phosphorylation, and NR activities (assayed with and without Mg2+) in spinach leaves. There appears to be a physiological role for both enzymes in mature source leaves (production of sucrose and amino acids for export), whereas NR is also present and activated by light in immature sink leaves. In mature leaves, there are significant diurnal changes in SPS and NR activities (assayed under selective conditions where phosphorylation status affects enzyme activity) during a normal day/night cycle. With both enzymes, activities are highest in the morning and decline as the photoperiod progresses. For SPS, diurnal changes are largely the result of phosphorylation/dephosphorylation, whereas with NR, the covalent modification is super-imposed on changes in the level of NR protein. Accumulation of end products of photosynthesis in excised illuminated leaves increased maximum NR activity, reduced its sensitivity of Mg2+ inhibition, and prevented the decline in activity with time in the light seen with attached leaves. In contrast, SPS was rapidly inactivated in excised leaves. Overall, NR and SPS share many common features of control but are not identical in terms of regulation in situ. 相似文献
2.
Correlation between apparent activation state of nitrate reductase (NR), NR hysteresis and degradation of NR protein 总被引:9,自引:3,他引:6
Nitrate reductase (NR) activity was measured in extracts fromspinach leaves exposed to light or prolonged darkness, and tovarious treatments provoking an artificial activation of theenzyme in the dark. NR activity was determined immediately eitherin the presence of Mg2+, which gives an estimation of the putative(actual) activity in situ (NRact), or in EDTA without preincubation,which gives an intermediate activity (NRint), or after a 30min preincubation with EDTA plus AMP plus Pi, which gives themaximum NR activity (NRmax). NRmax is thought to reflect totalNR protein contents. In the dark, NRact was usually very low. Dark inactivation wasprevented or reversed by feeding AICAR (5-aminoimidazole-4-carboxiamideribonucleoside), or by anaerobiosis, acid treatment or additionof uncoupler. During prolonged darkness, NRmax decreased, indicatingnet protein degradation with a half-time of 21 h. Conditionswhich caused an activation (dephosphorylation) of NR in thedark, slowed down NR protein degradation. This was also confirmedby Western blotting. Blockage of cytosolic protein synthesis with cycloheximide (CHX)did not accelerate NR protein degradation. In contrast, after5 h in the dark, NRact increased in CHX-treated leaves. As thisincrease was sensitive to PP2A-inhibitors, it was probably dueto NR dephosphorylation. However, extractable NR kinase andNR phosphatase activities were not changed by CHX treatment.Apparently, CHX interacted with the NR regulatory system indirectlyby affecting turnover of another protein. The increase from NRint to NRmax which occurred during preincubationof the leaf extract with EDTA plus AMP plus Pi was insensitiveto PP2A inhibitors and was interpreted as a hysteretic conversionof NR from an inactive into an active form. Hysteretic activationwas positively correlated to the NR phosphorylation state. Amodel is presented to explain the hysteretic behaviour of NRin relation to NA phosphorylation/ dephosphorylation. Overall, the data indicate that NR protein phosphorylation notonly controls the catalytic activity of NR, but also acts asa signal for NR protein degradation, with phospho-NR probablybeing a better substrate for protein degradation than the dephospho-form. Key words: Enzyme hysteresis, nitrate reductase, posttranslational modification, protein phosphorylation, protein turnover 相似文献
3.
Huber Steven C.; Nielsen Tom Hamborg; Huber Joan L. A.; Pharr David M. 《Plant & cell physiology》1989,30(2):277-285
Some species exhibit light activation of sucrose-phosphate synthase(SPS) in intact leaves. Twelve species which vary in extentof light modulation of SPS were studied to identify factorswhich regulate activation of the enzyme in situ. Leaves wereharvested in light and darkness, and SPS was assayed under highsubstrate (Vmax) or limiting substrate conditions (in the presenceof th inhibitor inorganic phosphate). The species tested fellinto three groups. In some species (Group I; barley and maize)light activation involved an increase in Vmax of the enzyme.In other species (Group II; spinach, swiss chard, sugarbeet,broad bean) light activation had no effect on Vmax but alteredcertain kinetic properties such that activation was only apparentwhen SPS was assayed with the limiting substration condition.Significantly, in some species (Group HI; soybean, pea, tobacco,Arabidopsis thaliana cucumber and melon) SPS activity was essentiallyunaffected by light/dark transitions. Phosphate sequesteringagents (mannose or gluco-samine) activated SPS in darkness inspecies which show light modulation (Groups I and II) but notspecies of Group III which do not light activate. Thus, changesin inorganic phosphate level may be one of the factors whichregulate the activation of SPS in situ. In addition, the catalyticactivity of SPS from species which exhibit light modulation(Groups I and II) is more strongly inhibited in vitro by inorganicphosphate (an allosteric effector) compared with the enzymeextracted from Group III species, which indicates that certainproperties of the enzyme itself may also vary among species.We conclude that species which do not exhibit light activationof SPS in intact leaves lack the mechanism responsible for thecovalent modification of enzyme activity (Walker and Huber 1989,Planta, in press) involved in light activation process. (Received October 14, 1988; Accepted January 5, 1989) 相似文献
4.
In vivo activation states of ribulose 1,5-bisphosphate carboxylase/oxygenase(RuBisCO; EC 4.1.1.39
[EC]
) in the dark and light phases were measuredin intact leaves of Phaseolus and radish. The activation statewas high in the dark and comparable to the activation stateunder illumination at saturating light intensity. Then, we examined,using RuBisCO purified from spinach leaves, a mechanism forthe activation of RuBisCO in the dark when the stroma is neutralizedand lossess Mg2+ partly. Activation was not obserevd when theenzyme was incubated at air-level CO2 and 10 mM Mg2+ at pH rangingfrom 6.2 to 7.5. However, the activation was highly promotedin this pH range when the activation mixture contained 10 mMinorganic phosphate. The activation state was 50 to 60% betweenpH 7.0 and 7.8 and maximum over pH 8.2 in the presence of 10mM inorganic phosphate. Studies of the initial rate of activationshow that the promotion of activation was through stabilizationof the active form of the enzyme by inorganic phosphate, notby altering the pKa of the activator -amino group of Lys-201.The physiological significance of the activation of RuBisCOby inorganic phosphate in the dark is discussed.
3 Present address: Department of Biochemistry, University ofNebraska, Lincoln, NE 68588-0664, U.S.A. 相似文献
5.
Salt Activation of Sucrose-Phosphate Synthase from Darkened Leaves of Maize and Other C-4 Plants 总被引:1,自引:0,他引:1
Maize leaf sucrose-phosphate synthase (SPS) has been shown tobe inactivated by protein phosphorylation in vitro, which appearsto be the mechanism of light modulation in situ [Huber and Huber(1991) Plant Cell Physiol. 32: 319326]. The catalyticactivity of the inactivated enzyme (dark form or in vitro inactivatedform) was strongly stimulated by high ionic strength in theassay mixture and at 0.4 M KC1 reached activities similar tothose obtained from illuminated leaves. Numerous salts wereeffective, but for most studies, 0.3 M KC1 was used. The salt-stimulationof enzyme activity was rapid and readily reversible and wasantagonized by the presence of ethylene glycol in the assay.The presence of salt was also found to reduce the IC50 (concentrationrequired for 50% inhibition) for p-chloromercuribenzenesulfonicacid. We postulate that phosphorylation of maize SPS inducesa conformational change in the protein (that affects both maximumcatalytic activity and sensitivity to Pi either through electrostaticor hydrophobic interactions which are affected by high ionicstrength. Salt stimulation of the deactivated enzyme extractedfrom darkened leaves was observed for a variety of C-4 plants,but not for any of the C-3 species tested. (Received October 23, 1990; Accepted January 7, 1991) 相似文献
6.
VIJAYARAGHAVAN S. JANAKI; GUPTA ADITYA; GUHA-MUKHERJEE SIPRA; SOPORY SUDHIR K. 《Journal of experimental botany》1982,33(4):705-716
Light-enhanced nitrate reductase (NR) activity was 8 times greaterthan the dark control. Exogenous application of sucrose, glucoseand fructose increased the induction of NR in the light as wellas in the dark, whereas glycolate had no effect. DCMU [3-(3,4-dichlorophenyl)-1, 1-dimethyl urea] completely inhibited thedevelopment of NR in light. Sucrose, when added with DCMU, reversedthis inhibitory effect NR in vivo was more stable in light thanin darkness, the half-lives being 9.6 h and 6.4 h, respectively.The addition of sucrose did not change the half-life of NR ineither light or darkness. Ammonium, the end product of the inorganicnitrogen assimilatory pathway, stimulated the NR activity whereasamino acids decreased it. Key words: Spirodela oligorrhiza, nitrate reductase, ammonium, light 相似文献
7.
Holbrook Gabriel P.; Campbell William J.; Rowland-Bamford Amanda; Bowes George 《Journal of experimental botany》1994,45(8):1119-1126
A comparative study was made of the inhibition of ribulose-1,5-bisphosphatecarboxylase-oxygenase (Rubisco) amongst six cultivars of Glycinemax L. Merr., associated with synthesis of 2-carboxyarabinitol1-phosphate (CA1P) during darkness. Significantly lower meanvalues of dark inhibition of Rubisco were observed in soybeancv. Davis than in cvs Bragg, Cobb, Hardee, Gordon, and Kirby.The CA1P synthesis/degradation cycle during dark/light transitionsremained operational in cv. Bragg plants grown at low irradiance(40 µmol photons m2 s1). However, CA1P synthesisand degradation rates were slower in the dark (t0.5 = 240 versus25 min), and light (t0.5 = 20 versus 3.8 min) respectively,as compared to plants grown at higher irradiance (550 µmolphotons m2 s1). In addition, the activation stateof Rubisco in low-light-grown plants showed only a small declineafter a transition to darkness. We conclude that (a) cultivar-dependentvariation occurs amongst soybeans with respect to CAlP regulationof Rubisco, and (b) soybeans acclimated to low irradiance maydepend more on CA1P synthesis/degradation to regulate Rubisco,and less on changes in the enzyme activation state. Key words: Activation state, Glycine max, photosynthesis, Rubisco, 2-carboxyarabinitol 1-phosphate 相似文献
8.
SYNOPSIS. Actomyosin was extracted from skeletal muscle of Coryphaenoides,a benthic fish living at 2,200 meters depth, at a temperatureof 2°C, or less, and at pressure of 3,000 psi. On SDS-ureaelectrophoresis on acrylamide gel, the actomyosin extracts yieldcomponents of apparent molecular weight 210,000 (myosin heavychains), 47,000 (actin), 35,000 (tropomyosin and/or troponinsubunits), and 13,000 (myosin light chains). The Mg2+-ATPaseof Coryphaenoides actomyosin shows a complex Arrhenius plot,with marked denaturation at temperatures above 30°C, anddiminished temperature sensitivity at temperatures below 15°C.Mg2+-ATPase is inhibited by pressure, with activation volumesof + 160 cc/mole at 25°C, and + 230 cc/mole at 2°C.Ca2+-ATPase of actomyosin exhibits the same pH, temperature,and pressure dependence as Ca2+-ATPase of myosin. The overalldata would be consistent with a positive activation volume thatis independent of temperature (to first approximation) and isrelated to the interaction of actin and myosin, and a negativeactivation volume that is temperature dependent and is relateddirectly to activation of myosin ATPase. The net effect appearsto be an adaptive mechanism whereby Mg2+-ATPase of Coryphaenoidesactomyosin is relatively insensitive to pressure and temperatureunder conditions encountered by the living fish. 相似文献
9.
Membrane-bound Mg++-activated ATPase activity in epidermal stripsfrom tobacco leaves (Nicotiana tabacum L. Samsun NN) was stimulatedby abscisic acid (ABA) when the strips were floated on ABA solutionin light or in darkness. The optimum ABA concentrations in lightand in darkness were 105 M and 106 M, respectively.Carbonyl cyanide m-chlorophenylhydrazone (CCCP) and N, N'-dicyclohexylcarbodiimide(DCCD) completely blocked the basal level membrane-bound epidermalATPase activity. ABAinduced membrane-bound epidermal ATPaseactivity was completely inhibited by CCCP, but only partly byDCCD. H+-influx into epidermal strips on a solution in light was lowerthan that in darkness. ABA stimulated H+-influx into epidermalstrips in light and in darkness. CCCP suppressed basal levelH+-influx, whereas DCCD did not. CCCP also suppressed ABA-inducedH+-influx, whereas DCCD did not. Interaction between H+-influxand membranebound epidermal ATPase activity is discussed. (Received May 23, 1978; ) 相似文献
10.
Inactivation of highly activated spinach leaf sucrose-phosphate synthase by dephosphorylation 总被引:7,自引:3,他引:4
Spinach (Spinacia oleracea L.) leaf sucrose-phosphate synthase (SPS) can be phosphorylated and inactivated in vitro with [γ-32P]ATP (JLA Huber, SC Huber, TH Nielsen [1989] Arch Biochem Biophys 270: 681-690). Thus, it was surprising to find that SPS, extracted from leaves fed mannose in the light to highly activate the enzyme, could be inactivated in an ATP-independent manner when desalted crude extracts were preincubated at 25°C before assay. The “spontaneous” inactivation involved a loss in activity measured with limiting substrate concentrations in the presence of the inhibitor, Pi, without affecting maximum catalytic activity. The spontaneous inactivation was unaffected by exogenous carrier proteins and protease inhibitors, but was inhibited by inorganic phosphate, fluoride, and molybdate, suggesting that a phosphatase may be involved. Okadaic acid, a potent inhibitor of mammalian type 1 and 2A protein phosphatases, had no effect up to 5 micromolar. Inactivation was stimulated about twofold by exogenous Mg2+ and was relatively insensitive to Ca2+ and to pH over the range pH 6.5 to 8.5. Radioactive phosphate incorporated into SPS during labeling of excised leaves with [32P]Pi (initially in the dark and then in the light with mannose) was lost with time when desalted crude extracts were incubated at 25°C, and the loss in radiolabel was substantially reduced by fluoride. These results provide direct evidence for action of an endogenous phosphatase(s) using SPS as substrate. We postulate that highly activated SPS contains phosphorylated residue(s) that increase activation state, and that spontaneous inactivation occurs by removal of these phosphate group(s). Inactivation of SPS in vivo caused by feeding uncouplers to darkened leaf tissue that had previously been fed mannose in the dark, may occur by this mechanism. However, there is no evidence that this mechanism is involved in light-dark regulation of SPS in vivo. 相似文献
11.
In response to in situ dark modulation, or in vitro ATP preincubationof higher plant nitrate reductase, Mg2+ inhibits NADH:nitratereductase activity but not MV:nitrate reductase activity incrude extracts. Also for the purified enzyme the complete NADH:nitratereductase activity is inhibited by Mg2+, but not the partialMV:nitrate reductase or Cyt c reductase activities. (Received October 13, 1993; Accepted January 24, 1994) 相似文献
12.
Sripathi Sajja S. V. Munjal A. A. Kale R. M. Naik 《Journal of plant biochemistry and biotechnology.》2006,15(2):135-137
In vivo nitrate reductase (NR) activity declined gradually either in absence or presence of Mg2+ In dark grown plants of spinach. The increased sensitivity of the extracted NR from the dark grown plants to Mg2+ and ATP is indicative of the post-translational modification as one of the mechanisms to control NR activity. The response of extracted NR was gradual and not instantaneous suggesting a complex interplay of NR regulation, as the dark acclimatized plants when exposed to light caused significant nitrate reduction within 15 min of light exposures even in the presence of Mg2+ and ATP. 相似文献
13.
DiPolo R Berberián G Beaugé L 《American journal of physiology. Cell physiology》2000,279(5):C1631-C1639
We investigated the role of intracellular Mg2+(Mgi2+) on the ATP regulation ofNa+/Ca2+ exchanger in squid axons and bovineheart. In squid axons and nerve vesicles, the ATP-upregulated exchangerremains activated after removal of cytoplasmic Mg2+, evenin the absence of ATP. Rapid and complete deactivation of theATP-stimulated exchange occurs upon readmission ofMgi2+. At constant ATP concentration, the effectof intracellular Mg2+ concentration([Mg2+]i) on the ATP regulation of exchangeris biphasic: activation at low [Mg2+]i,followed by deactivation as [Mg2+]i isincreased. No correlation was found between the above results and thelevels of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] measured innerve membrane vesicles. Incorporation ofPtdIns(4,5)P2 into membrane vesicles activates Na+/Ca2+ exchange in mammalian heart but not insquid nerve. Moreover, an exogenous phosphatase prevents MgATPactivation in squid nerves but not in mammalian heart. It is concludedthat 1) Mgi2+ is an essentialcofactor for the deactivation part of ATP regulation of the exchangerand 2) the metabolic pathway of ATP upregulation of theNa+/Ca2+ exchanger is different in mammalianheart and squid nerves. 相似文献
14.
Bull R Finkelstein JP Humeres A Behrens MI Hidalgo C 《American journal of physiology. Cell physiology》2007,293(1):C162-C171
Despite their relevance for neuronal Ca2+-induced Ca2+ release (CICR), activation by Ca2+ of ryanodine receptor (RyR) channels of brain endoplasmic reticulum at the [ATP], [Mg2+], and redox conditions present in neurons has not been reported. Here, we studied the effects of varying cis-(cytoplasmic) free ATP concentration ([ATP]), [Mg2+], and RyR redox state on the Ca2+ dependence of endoplasmic reticulum RyR channels from rat brain cortex. At pCa 4.9 and 0.5 mM adenylylimidodiphosphate (AMP-PNP), increasing free [Mg2+] up to 1 mM inhibited vesicular [3H]ryanodine binding; incubation with thimerosal or dithiothreitol decreased or enhanced Mg2+ inhibition, respectively. Single RyR channels incorporated into lipid bilayers displayed three different Ca2+ dependencies, defined by low, moderate, or high maximal fractional open time (Po), that depend on RyR redox state, as we have previously reported. In all cases, cis-ATP addition (3 mM) decreased threshold [Ca2+] for activation, increased maximal Po, and shifted channel inhibition to higher [Ca2+]. Conversely, at pCa 4.5 and 3 mM ATP, increasing cis-[Mg2+] up to 1 mM inhibited low activity channels more than moderate activity channels but barely modified high activity channels. Addition of 0.5 mM free [ATP] plus 0.8 mM free [Mg2+] induced a right shift in Ca2+ dependence for all channels so that [Ca2+] <30 µM activated only high activity channels. These results strongly suggest that channel redox state determines RyR activation by Ca2+ at physiological [ATP] and [Mg2+]. If RyR behave similarly in living neurons, cellular redox state should affect RyR-mediated CICR. Ca2+-induced Ca2+ release; Ca2+ release channels; endoplasmic reticulum; thimerosal; 2,4-dithiothreitol; ryanodine receptor 相似文献
15.
The temporal changes of potassium (K+) and sodium (Na+) contentsin the growing front of Neurospora crassa (al-2, bd strain)grown on solid medium showed circadian rhythms which persistedfor at least 45 h in the dark. The K+ content reached a maximumat about 10 and 30 h after the transfer from light to darkness,while the Na+ content was at a minimum at these times. Boththe rhythms were set off by the light to dark transition andwere not observed in constant light. The phase of the circadianrhythm of conidiation of this strain was delayed by 5 h by exposureto 50 min of white light (photon fluence rate 20.7 W/m2) 7 hafter the light to dark transition. The same exposure significantlychanged the ratio of K+ to Na+ content in the growing frontmeasured 8 h after the exposure.
3 Present address: Pesticides Research Laboratory, TakarazukaResearch Center, Sumitomo Chemical Co., Ltd., 2-1, 4-chome,Takatsukasa Takarazuka, Hyogo 665, Japan. (Received June 26, 1984; Accepted January 11, 1985) 相似文献
16.
NADP malic enzyme (EC 1.1.1.40
[EC]
) from leaves of two C4 speciesof Cyperus (C. rotundus and C. brevifolius var leiolepis) exihibiteda low level of activity in an assay mixture that contained lowconcentrations of Cl. This low level of activity wasmarkedly enhanced by increases in the concentration of NaClup to 200 mM. Since the activity of NADP malic enzyme was inhibitedby Na2SO4 and stimulated by relatively high concentration ofTris-HCl (50100 mM, pH 78), the activation ofthe enzyme by NaCl appears to be due to Cl. Variationsin the concentration of Mg2+ affected the KA (the concentrationof activator giving half-maximal activation) for Cl,which decreased from 500 mM to 80 mM with increasing concentrationsof Mg2+ from 0.5 mM to 7 mM. The Km for Mg2+ was decreased from7.7 mM to 1.3 mM with increases in the concentration of NaClfrom zero to 200 mM, although the increase of Vmax was not remarkable.NADP malic enzyme from Cyperus, being similar to that from otherC4 species, was able to utilize Mn2+. The Km for Mn2+ was 5mM, a value similar to that for Mg2+. The addition of 91 mMNaCl markedly decreased the Km for Mn2+ to 20 +M. NADP malicenzyme from Setaria glauca, which contains rather less Clthan other C4 species, was inactivated by concentrations ofNaCl above 20 mM, although slight activation of the enzyme wasobserved at low concentrations of NaCl at pH7.6. (Received February 20, 1989; Accepted June 12, 1989) 相似文献
17.
Seeds of 19 native British herbaceous species (14 grasses andfive forbs) were exposed to white light at three photon fluencerates: high (192 mol m2 d1), medium (9·6mol m1 d1) and low (2·3 mol m2 d2) These photon doses have been found by previous workers to inhibitgermination in several species. High and low photon doses wereapplied only as continuous light, but the medium dose was appliedas both continuous light and as a 12 h light/12 h dark photoperiod.All four treatments, plus a dark control, were carried out at15 °C; the high and low doses were also applied with a dailyalternation of 10/20 °C. The majority of species (15) fell into one of two groups. Inseven species germination was relatively high and consistentacross all treatments, including darkness; in the other eightspp germination was inhibited only in darkness. Mostly thesedata confirmed published results for the same species In contrast in Agrostis capillaris and A. stolonifera germinationwas high only at alternating temperatures, irrespective of photondose, but was also slightly promoted by a constant temperaturecombined with light/dark alternations. Only in Bromus sterilisand B. ereclus was germination inhibited by light, in B. erectusat all photon doses and in B. sterilis only at the highest photondose These results suggest that inhibition of germination by highirradiance light is not widespread among native British species Aira caryophyllea, Arrenatherum elatius, Festuca ovina, F. rubra, Hordeum murinum, Milhim effusum, Silene dioica, Achillea millefolium, Brachypodium syhaticum, Digitalis purpurea, Holcus lanatus, Leucanlhemum vulgare, Phleum pratense, Poa trivialis, Taraxacum officinale, Agrostis capillaris, A. stolonifera, Bromus erectus, B. sterilis, seed, dormancy, germination, light, High irradiance reaction, alternating temperatures, photoperiod 相似文献
18.
BIELEFELD ULRICH; KORTJE KARL HEINZ; RAHMANN HINRICH; BECKER WILHELM 《Journal of Molluscan Studies》1993,59(3):323-338
In the freshwater snail Biomphalaria glabrata, the outer mantleepithelium and the transitional epithelium from the outer mantleepithelium to the belt are characterized by apical vesiclesof different electron density and vacuoles including lipid dropletsand fibrillar structures. Wide intercellular spaces predominatein the transitional epithelium. In addition to belt desmosomes,freeze fracture studies detect septate junctions as apical intercellularjunctions. The permeability of the septate junctions is testedby injecting anaesthetized snails with solutions containingperoxidase and lanthanum-nitrate. The septate junctions appearto be impermeable for the protein and inhibit permeation ofthe ion. Alkaline phosphatase is detected at the light microscope levelin the transitional and outer mantle epithelium. At the electronmicroscope level localization of alkaline phosphatase is restrictedto the apical and basal cell membranes of the same epithelia.An ATPase with low affinity to Ca2+ and Mg2+ ions is observedin the lumen of vacuoles in the proximal belt, the transitionaland the outer mantle epithelium. The possible role of the vacuolesas a site of synthesis or modification of the intercrystallinematrix is discussed. A high affinity Ca2+/Mg2+ ATPase is detectedwith the help of Electron Spectroscopic Imaging in the cellmembranes and in membranes of the rER. A model for solute transport through the epithelia to the extrapallialspace is proposed. (Received 18 August 1992; accepted 4 January 1993) 相似文献
19.
Sanada Yukika; Ueda Hiroko; Kuribayashi Kazuhiro; Andoh Toshiya; Hayashi Fumio; Tamai Naoto; Wada Keishiro 《Plant & cell physiology》1995,36(6):965-970
Proline accumulation was determined in a facultative halophyte,Mesembryanthemum crystallinum and glycophytes, barley (Hordeumvulgare L.) and wheat (Triticum aestivum L.) Proline accumulationpreceded the shift of CAM in M. crystallinum and did not occurin the continuous darkness. The novel light-dark change of prolinelevel (high in the light and low in the dark) was observed inleaves of all three plants. Proline levels of shoots in barleyand wheat also showed the same light-dark change, suggestingthat proline accumulated in the leaves in the light was nottranslocated to other tissues in the dark period. These resultssuggest that proline has a bifunctional role in the acclimationto high salt stress; an osmoregulant role in the light, anda substrate for dark respiration to supply energy to compartmentationof ions into vacuole in the dark.
1Present address: Kyoto Biological Res. Lab., Bio-Chiba Inc.Watsuka,Soraku, Kyoto, 619-12 Japan
2Present address: Kobayashi Pharmaceutical Co., Ltd. Doshomachi,Chuo-ku, Osaka, 541 Japan 相似文献
20.
Dimethipin (2,3-Dihydro-5,6-dimethyl-1,4-dithiin 1,1,4,4-tetraoxide) Effects on Soybean Seedling Growth and Metabolism 总被引:1,自引:0,他引:1
Three-day-old dark-grown soybean [Glycine max (L.) Merr.] seedlingswere transferred to 2 mM CaSO4 or 105 M dimethipin in2 nM CaSO4 and root-fed via liquid culture. Plants were placedin continuous darkness or in continuous white light (200 µE.m2?s11,PAR) at 25?C. Dimethipin inhibited root and shoot elongationin dark-grown plants after 24 h and 48 h, respectively. In thelight, root elongation was inhibited also after 24 h, but hypocotylelongation was not significantly affected. Extractable phenylalanineammonia-lyase (PAL) activity per axis in dimethipin-treateddark-grown axes was not generally affected but, in the lightdimethipin caused a significant decrease in PAL activity (24to 96 h). Total soluble hydroxyphenolics in axes were not affectedby dimethipin in light- or dark-grown plants. Anthocyanin andchlorophyll levels were lowered in hypocotyls of dimethipin-treatedplants after 48 to 96 h. Soluble protein in hypocotyls of light-or dark-grown seedlings was not substantially affected by dimethipin.Nitrate reductase (NR) activity (per organ) was generally notaffected by dimethipin in light-grown cotyledons, but in theroots of these seedlings, NR activity was significantly decreased.Proteolytic enzyme activity using three substrates (leucine-p-nitroanilide,LPNA; proline-p-nitroanilide, PPNA; and benzoylarginine-p-nitroanilide,BAPA) indicated little effect on enzyme activities per organin roots and hypocotyls. These data suggest that dimethipinat low concentrations can cause significant growth inhibitionin soybean seedlings grown in either light or darkness and thatfurthermore, extractable activities of some enzymes associatedwith nitrogen metabolism and secondary metabolism are alteredby this chemical. Light also plays a role in the activity ofthis chemical. (Received November 29, 1983; Accepted January 25, 1984) 相似文献