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1.
《Journal of experimental botany》1960,11(2):150
On page 235, Table I: Equation (1) for Node 4 should read A/Ac=0·840+0·0006Ac;Equation (2) for Node 4 should read A=0·89Acand Equation (2) for Node 510 should read A=0·813Ac. 相似文献
2.
Bean plants (Phaseolus vulgaris L. cv. Fardenlosa Shiny) werelabelled with carbon-11 via their first trifoliate leaves when3-weeks-old and the transient inhibitions of translocation causedby the application of ammonium chloride solutions (10 mol m3)to a peeled region of stem were studied. At pH 6·5 theammonium was without effect. At pH 11·0 even a briefapplication inhibited translocation for many minutes, whilelonger applications inhibited translocation for considerablylonger. Solutions of 10 mol m3 sodium chloride were withouteffect at either pH. At pH 6·5 ammonium chloride solution contains predominantlyammonium ions (NH4+) and at pH 11·0 predominantly dissolvedammonia gas (NH3). Hence we conclude that phloem transport withinbean stems is inhibited by dissolved ammonia gas but not ammoniumions. Key words: Phloem translocation, transient inhibition, ammonia, ammonium ion 相似文献
3.
Studies of in vivo nitrate reductase activity (NRA) in Eichhorniacrassipes showed that adding 5% isopropanol gave highest NRAin all parts of the plant, but it was also necessary to flushthe assay media containing leaves with N1 to obtain the maximalactivity. There were differences in the pH optima for NRA, theroot optimum being 6·5 leaf 7·58·0,and the petiole showing a major peak at 6·5 and a minorpeak at 7·.58·0. Possible significancesof these differences are discussed. Nitrate reductase activity, Eichhornia crassipes 相似文献
4.
The hydrogen ion-sensitive liquid-membrane micro-electrode,as described by Amman, Lanter, Steiner, Schulthess, Shijo, andSimon (1981) has been developed further and made applicablefor turgescent plant cells even with tough cell walls, by treatmentwith polyvinylchloride (PVC). Such an electrode is slower (t=510s) than the untreated electrode (t=26 s), but displays5559 mV/pH-unit between pH 4·3 and 9·0,and is almost insensitive towards different buffers and K+.The electrodes are usable on more than one cell and have stillgood recalibration properties. Testing the electrodes on 11different cell types of Riccia fluitans, Sinapis alba, Zea mays,Avena sativa, Kalanchöe daigremontiana, Lemna gibba andChara corallina, we find the internal pH slightly alkaline (7·17·6)in ten cases (exception: old rhizoids of Riccia, pH1=4·8).From that we conclude that the pH-electrode measures in thecytosol. According to the different plant material, severalprocedures for internal pH-measurements are presented and supportedby data: Application of cyanide and acetic acid causes internalacidification. Light-off transiently alkalinazes, light-on transientlyacidifies the internal pH. The advantages and limitations ofthe method are critically discussed, and it is concluded thatthis electrode is a powerful tool in plant physiology. Key words: Internal pH, pH-sensitive micro-electrode 相似文献
5.
Extracts from tissue cultures of crown-gall from Parthenocissuscatalysed the destruction of indoleacetic acid in vitro withoptimum activity at pH 4·5. The presence of two co-factors,Mn++ and 2,4-dichlorophenol, was necessary for this activity,which was found to be strictly aerobic. Chlorogenic acid, caffeic acid, scopoletin, ferulic acid, andgibberellic acid markedly inhibited IAA-destruction. Chlorogenicacid inhibition was reversed by the addition of H2O2. Chlorogenicacid was not oxidized by the IAA-destroying system and did notbehave as a competitive inhibitor. The IAA-oxidase extract manifested peroxidase and phenolaseactivity with catechol and pyrogallol as substrates. However,this activity was greater at pH 7·0 than at the optimumfor IAA-oxidase activity, pH 4·5. Further evidence ofthe existence of these two enzymes in the intact tissue wasdemonstrated by histochemical studies. In tissue slices, peroxidaseactivity was very high and widely distributed while phenolaseactivity was low and restricted to localized centres of thetissue. 相似文献
6.
Transient Cytoplasmic pH Changes in Correlation with Opening of Potassium Channels in Eremosphaera 总被引:1,自引:0,他引:1
Steigner, W. Khler, K., Simonis, W. and Urbach, W. 1988. Transientcytoplasmic pH changes in correlation with opening of potassiumchannels in Eremosphaera.J. exp. Bot. 39: 2336. The role of the cytoplasmic pH (pHc) of Eremosphaera viridisin the signal transduction chain after light-off from the chloroplaststo the K+ channels in the plasmalemma of this unicellular algawas investigated. The temporary opening of K+ channels is indicatedby a transient hypcrpolarization (TP). To record rapid changesof pHc, continuous measurements with pH sensitive micro-electrodeswere carried out. (i) Under normal conditions pHc in the light(7·56 ±0·2) did not differ from pHc inthe dark (7·62 ±0·2). (ii) The vacuolepH ranged between 4·8 and 5·2. (iii) After light-offa rapid transient acidification of pHc O19±0·07occurred and a TP was released, (iv) In every case, the startof the transient acidification after light-off preceded thehyperpolarization by about 3s. (v) Light-on caused a rapid transientalkalinization but never a TP. (vi) Change to acid externalmedium (3.2) transiently acidified the cytoplasm and was ableto release a TP. (vii) After addition of NH4Cl, pHc again showeda rapid transient acidification and the release of a TP. The origin of the protons appearing in the cytoplasm after light-offis discussed critically with respect to the buffer capacity.Either direct or indirect translocation is a possible mechanismfor the movement of H+ from the chloroplasts into the cytoplasm.The intracellular acidification and its relation to the openingof potassium channels in the plasmalemma leads us to suggestthat a sudden change of pHc is a potent internal signal factorin Eremosphaera viridis. Key words: Cytoplasmic pH, transient potential, K+channels, Eremosphaera viridis 相似文献
7.
Six kinds of acid phosphatases were solubilized with TritonX-100 from the cell wall (W-I, W-II), mitochondrial (M-I, M-II,M-III) and microsomal (Ms) fractions of bean hypocotyl, andthey were partially purified by using Sephadex gel filtrationand DEAE-cellulose column chromatography. Acid phosphatasesfrom the soluble fraction were also fractionated into 12 isozymesby electrophoresis, and the properties of the isozymes werecompared. The soluble isozymes showed pH optima at 5·0,5·3 and 5·6; the isozymes possessed high affinityto p-nitrophenyl phosphate and ADP, and their mol. wts rangedfrom 30000 to 45000. Among the solubilized phosphatases, W-I,M-I and M-III showed maximum activity at pH 5·0 and theirmol. wts were between 50000 and 110000. W-I proved to have highaffinity to ATP and bis-p-nitrophenyl phosphate as M-I did top-nitrophenyl phosphate and M-III to phenyl phosphate. The characteristicsof these solubilized isozymes were different from those of thesoluble isozymes. On the contrary, W-II, M-II and Ms were quitesimilar to those of the solubles in pH optima, substrate specificity,Km value, affinity to DEAE-cellulose and gel electrophoreticpatterns. These results suggest that W-II, M-II and Ms werederived from the soluble isozymes. Phaseolus vulgaris L., bean, hypocotyl, acid phosphatases, Michaelis constant 相似文献
8.
Aluminium Effects on ATPase Activity and Lipid Composition of Plasma Membranes in Sugar Beet Roots 总被引:3,自引:1,他引:2
The effect of aluminium (Al) in vivo and in vitro on root plasmamembranes has been studied in two sugar beet (Beta vulgarisL.) cultivars, Monohill (Al-sensitive) and Regina (relativelyAl-tolerant). Although Al in vitro inhibited the MgATPase inan uncompetitive way for both cultivars raised in the absenceof Al, the specific K+-activation of the MgATPase was only inhibitedby Al in cv. Monohill. Arrhenius analysis of the MgATPase activity showed that theeffect of Al in vitro depended on whether or not the plantswere exposed to Al in vivo. Al treatment in vitro of the MgATPasefrom control plants cultivated at a low pH (5·4) causedan increase in the phase transition temperature from 17 to 22°C. Only at a higher pH range (pH 6·1) could a secondtransition temperature be induced (at 9 °C). By additionof Al in vitro to plants cultivated with Al at pH 5·4,the slopes of the activity plots did not change. Aluminium changedthe Km of the ATPase for MgATP in an opposite way by treatmentin vivo and in vitro. Lipid analyses of the plasma membranes showed that the acylcomposition differed little following Al treatment in vivo,but that the ratio of phosphatidylcholine: phosphatidylethanolamineincreased. The changes correlated with the observed change inthe Km for the MgATPase. We conclude that the main effect ofAl on the MgATPase is not due to the formation of an Al-ATPcomplex. Instead, Al may bind to the membrane-bound enzyme(s)and/or modify the lipid environment. Key words: Aluminium, ATPase, Beta vulgaris, lipids 相似文献
9.
Perianth MP, gynoecium MG, and androecium MA dry-weight biomass(in g) of 39 species of perfect flowers was measured. Thesedata were pooled with published data from an additional 51 speciesand used to determine size-dependent variations in (MG and MA)in terms of the hypothesis that the quotient of MG and MA exceeds1·0 for out-breeding (xenogamous) species and less than1·0 for in-breeding (autogamous) species. Ordinary leastsquare regression of the pooled data (n = 90) showed MG = 0·118M0·916P (r2 = 0·884) and MA = 0·186 M0·975P(r2 = 0·865), indicating that the biomass of the gynoeciumproportionally decrease as floral size increases. The exponentsof these regressions indicate that the ratio of gynoecial toandroecial biomass decreased with increasing floral size suchthat comparatively small flowers (MP < 0·0021 g) hadMG/MA > 1·0 (predicted for 'out-breeders') while comparativelylarger flowers (MP > 0·0021 g) had MG /MA < 1·0(predicted for 'in-breeders'). Thus, on average, the type ofbreeding system was a size-dependent phenomenon. To test whether the biomass of a floral organ-type is a legitimateindicator of gender reproductive effort, the biomass (in g)of stamen filaments Mm and anther sacs MAS of 39 species wasdetermined. Least square regression of these data showed MAS= 0·188 M0·854fil (r2 = 0·967), indicatingthat species with larger stamen filaments, on the average, boreproportionally smaller anther sacs and thereby cautioning againstthe uncritical use of the allocation of biomass to floral organ-typeas a strict gauge of gender-function investment. To determine whether the loss of one gender-function resultsin proportional reallocation of biomass to the remaining gender-function,the size-dependency of androecial and gynoecial biomass wasdetermined for a total of 33 perfect and imperfect flowers ofCucumis melo. Regression of the data obtained from perfect flowersyielded MA = 0·402 M1·47P (r2 = 0·898)and MG = 4·63 M1·36P (r2 = 0·842). SinceMG/MA M0·11P , the biomass allocation to the gynoeciumrelative to the androecium decreased with increasing floralsize. This result was consistent with the broad interpecificcomparison based on 90 species with perfect flowers . Regressionof the data for imperfect flowers yielded MA = 0·151M1·02P (r2 = 0·675) and MG = 4·68 M1·47P(r2 = 0·996), indicating a near allometric relation forthe androecium and a strong positive anisometry for the gynoecium.Thus, for flowers of comparable size, a loss of female genderobtains a modest to significant again in androecial biomasswhereas the loss of male gender yields only a slight increasein gynoecial biomass. Collectively, the results of these studies indicate that biomassallocation patterns are size-dependent phenomena whose complexitieshave been largely ignored in the literature.Copyright 1993,1999 Academic Press Allometry, floral biomass, reproduction 相似文献
10.
Respiratory oxygen consumption by roots was 1·4- and1·6-fold larger in NH+4-fed than in NO-3-fed wheat (Triticumaestivum L.) and maize (Zea mays L.) plants respectively. Higherroot oxygen consumption in NH+4-fed plants than in NO-3-fedplants was associated with higher total nitrogen contents inNH+4-fed plants. Root oxygen consumption was, however, not correlatedwith growth rates or shoot:root ratios. Carbon dioxide releasewas 1·4- and 1·2-fold larger in NO+3-fed thanin NH+4-fed wheat and maize plants respectively. Differencesin oxygen and carbon dioxide gas exchange rates resulted inthe gas exchange quotients of NH-4-fed plants (wheat, 0·5;maize, 0·6) being greatly reduced compared with thoseof NO-3-fed plants (wheat, 1·0; maize, 1·1). Measuredrates of HCO-3 assimilation by PEPc in roots were considerablylarger in 4 mM NH+4-fed than in 4 NO-3 plants (wheat, 2·6-fold;maize, 8·3-fold). These differences were, however, insufficientto account for the observed differences in root carbon dioxideflux and it is probable that HCO-3 uptake is also importantin determining carbon dioxide fluxes. Thus reduced root extension in NH+4-fed compared with NO-3-fedwheat plants could not be ascribed to differences in carbondioxide losses from roots.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize assimilation, ammonium assimilation, root respiration 相似文献
11.
SELLSTEDT ANITA; STAHL LENA; MATTSSON ULRIKA; JONSSON KERSTIN; HOGBERG PETER 《Journal of experimental botany》1993,44(12):1749-1755
Three methods were used to study N2 fixation and effects ofwater deficit on N2 fixation: C2H2 reduction assay (ARA), 15Ndilution technique and accumulated N content. In addition, 15Ndilution was calculated both in a traditional way and in a modifiedway, which takes into consideration N and 15N content for theplants before the experiment started. The three methods wereapplied on the following Rhizobium-symbioses: Acacia albidaDel (Faidherbia albida (Del) A. Chev.) and Leucaena leucocephala(Lam) de Wit., and the Frankia-symbiosis Casuarina equisetifoliaL. The plants wereabout 4-months-old when they were harvested. Nitrogen derived from N2 fixation in control plants of Acaciaalbida was 54·2 mg as measured with ARA, while it was28·5 mg as measured with the 15N dilution technique,compared to 30·7 mg calculated as accumulated N. In comparison,L. leucocephala fixed 41·6 mg N (ARA), 53·5 mgN(15N dilution technique) and 56·3 mg N (accumulatedN). The Frankia-symbiosis had fixed 27·4 mg N as measuredby ARA, 8·1 mg N as measured by 15N dilution techniqueand 12·3 mg N as accumulated N. There were no differencesbetween the estimates based ontraditional and modified waysof calculating 15N dilution. The immediate effect of water deficit treatment on N2 fixationwas continuously measured inall species with ARA, which startedto decrease approximately 10 d after the initiation of the treatment,and declined to less than 5% of the initial level after 2128d. The decrease in the amount of N derived from N2 fixation wasstudied in L. leucocephala during the period of treatment. Therewas a 26% decrease in amount of N derived from N2 fixation asresult of water deficit (as measured with ARA), while the decreasewas 23% when measured withboth the 15N dilution method and asaccumulated N. The three different methods for measuring N2 fixation and effectsof water deficit on N2 fixation are discussed. Key words: Acacia albida, ARA, Casuarina equisetifolia, Leucaena leucocephala, 15N dilution, N2N fixation, water deficit 相似文献
12.
Maximum activity of phosphoenolpyruvate carboxylase (PEPC, EC4.1.1.31) was detected at the stationary phase of growth ofCatharanthus roseus cells in a heterotrophic culture. The activityof PEPC, after partial purification by fractionation with ammoniumsulphate and chromatography on Q-Sepharose, was greatly influencedby pH. The Km of phosphoenolpyruvate (PEP) was 23 µM atpH 8·0 and 45 µM at pH 7·4. Malate, aspartate,citrate, ATP, pyrophosphate and Pi acted as inhibitors of PEPC,but the extent of inhibition varied in each case with the pHof the reaction mixture. By contrast, glucose-6-phosphate, fructose-1,6-bisphosphateand acetyl-CoA, known as stimulators of the activity of PEPCfrom other sources, had little or no effect on the activityof the partially purified PEPC. The possible role and mechanismof regulation of PEPC in C. roseus cells are discussed.Copyright1994, 1999 Academic Press Catharanthus roseus, Apocynaceae, Madagascar periwinkle, suspension culture, phosphoenolpyruvate carboxylase, enzyme kinetics, glycolysis 相似文献
13.
Kelly Grahame J.; Mukherjee Ute; Holtum Joseph A. M; Latzko Erwin 《Plant & cell physiology》1985,26(2):301-307
Phosphofructokinase was purified 585-fold from Chlorella pyrenoidosaby using a combination of ammonium sulphate fractionation, filtrationthrough Sepharose 4B and chromatography on DEAE-Sephacel. Enzymestability was maintained by the presence of 50 mM Pi at pH 6.6.The optimum pH for activity was 7.7. Concentrations of substratesrequired to achieve half maximal velocity in the standard assaywere 9 µM (ATP) and 0.2 mM (fructose-6-P). ATP above 0.5mM was inhibitory. Enzyme activity was inhibited by high concentrations(10100 mM) of Pi but lower concentrations (15mM) were effective in relieving the influence of other inhibitorssuch as P enolpyruvate. Inhibition by P-enolpyruvate was greaterat lower pH and with less Pi in reaction mixtures: 50% inhibitioncould be attained with 0.1 mM P-enolpyruvate. Fructose-2,6-bisphosphate,which was shown to be present in Chlorella, had no effect onthe phosphofructokinase. Chlorella appeared to contain onlyone form of phosphofructokinase, possibly in the chloroplast.No pyrophosphate :D-fructose-6-P 1-phospho transferase activitycould be detected. (Received February 20, 1984; Accepted December 5, 1984) 相似文献
14.
The kinetic properties of phosphoenolpyruvate (PEP) carboxylasehave been studied among several Flaveria species: the C3 speciesF. cronquistii, the C3C4 species F. pubescens and F.linearis, and the C4 species F. trinervia. At either pH 7 or8, the maximum activities (in µmol.mg Chl1.h1)for F. pubescens and linearis (187513) were intermediateto those of the C3 species (1219) and the C4 species(2,1822,627). The response curves of velocity versusPEP concentration were hyperbolic for the C3 and C3C4species at either pH 7 or 8 while they were sigmoidal for theC4 species at pH 7 and hyperbolic at pH 8. The Km values forPEP determined from reciprocal plots were lowest in the C3 species,and of intermediate value in the C3C4 species comparedto the K' values of the C4 species determined from Hill plotsat either pH 7 or 8. Glucose-6-phosphate (G6P) decreased theKm values for PEP at both pH 7 and 8 in the C3 and C3C4species. In the C4 species, G6P decreased the K' values at pH8 but increased the K' values at pH 7. In all cases, G6P hadits effect by influencing the activity at limiting PEP concentrationswith little or no effect on the maximum activity. At pH 8 andlimiting concentrations of PEP the degree of stimulation ofthe activity by G6P was greatest in the C4 species, intermediatein F. linearis, a C3C4 species, and lowest in the C3species. In several respects, the PEP carboxylases of the C3C4Flaveria species have properties intermediate to those of theC3 and C4 species. (Received April 30, 1983; Accepted August 22, 1983) 相似文献
15.
The Effect of Brassica oleracea Stigma Extracts on the Germination of B. oleracea Pollen in a Thin Layer Chromatographic Bioassay 总被引:1,自引:0,他引:1
Hodgkin, T. and Lyon, G. D 1986. The effect of Brassica oleraceastigma extracts on the germination of B. oleracea pollen ina thin layer chromatographic bioassay.J. exp. Bot. 37:406411. A procedure for germinating Brassica oleracea pollen on thinlayer chromatography plates pretreated with 20 mol m3tris(hydroxymethyl) methyl-aminopropanesulphonic acid (TAPS)buffer, pH 8·0 has been devised and used to detect pollengermination inhibitors in B. oleracea stigma extracts. Inhibitory zones in extracts of stigmas, unpollinated, or collected0·5, 4, 8 and 24 h after self- or cross-pollination,differed little in RF values and sizes. Extracts of stigmascollected 1 h and 2 h after self-pollination gave a small additionalinhibitory zone which was not detected in 1 h and 2 h cross-pollinatedstigma extracts. The results showed some differences from thoseobtained using Petunia hybrida pollen germinated on T.L.C. platesthat were not pretreated with buffer. The nature of the differencesbetween the two bioassays is discussed and some possible reasonsfor them indicated. Key words: Pollen, germination inhibitors, self-incompatibility, Brassica oleracea 相似文献
16.
Wheat (Triticum aestivum L.) embryos form in dynamically-regulatedovular environments. Our objectives were to improve developmentof cultured immature wheat embryos by simulating, in vitro,abscisic acid (ABA) levels and O2 tensions as found in wheatovules during zygotic embryogenesis. We characterized from intactwheat kernels embryo respiration, embryo morphology and embryoand endosperm + ABA levels at 13, 19 and 25 d post-anthesis(DPA). Young (13 DPA) embryos were then excised and culturedin vitro, where they were exposed to 0·2 or 2·Ommol m3 ±ABA and 2.·1, 2·5 or 7·4mol m3 (6, 7 and 21%, respectively) gaseous O2. At 6and 12 d in culture, + ABA levels, embryo respiration and embryomorphology were characterized by treatment. Thirteen-day-oldembryos from two different plant populations differed by 17-foldin initial ABA content. However, this difference did not affectprecocious germination in vitro, nor did it affect the amountof exogenous ABA required to reduce precocious germination by40%. In this respect, embryos from both populations were equallysensitive to exogenous ABA. Cavity sap O2 levels (2·1to 2·5 mol m3) were much more effective in preventingprecocious germination of cultured embryos than were cavitysap levels of ABA (0·2 to 2·0 mmol m3).The combination of physiological levels of both ABA and O2 largelynormalized DW accumulation and embryo morphology without alteringendogenous + ABA levels. Residual respiration of cultured embryoswas higher than that of embryos grown in situ, and was not influencedby the exogenous O2 and ABA treatments Key words: Abscisic acid, embryo development, oxygen tensions, respiration, wheat 相似文献
17.
Shelp, B. J. 1987. The composition of phloem exudate and xylemsap from broccoli (Brassica oleracea var. italica) suppliedwith NH+4, NO3 or NH4NO3.J. exp. Bot. 38: 16191636. The detailed composition of xylem sap and exudate from stemincisions of attached inflorescences of broccoli (Brassica oleraceavar. italica) was compared in plants supplied with NH+4, NO3or NH4NO3. A phloem origin for the exudate was suggested fromthe high levels of sugars (71133 mg cm-3), amino acids(8·1-26·7 mg cm3) and K. (2·33·8mg cm3), the low levels of NO3 and Ca, the high C: N (w/w) ratios(8·333), and the alkaline pH (7·27·3).In contrast, the xylem sap was mildly acidic (pH 5·66·0),and possessed lower levels of all organic and inorganic solutesbut NO3 and Ca, and lower ratios of K: Ca, Mg: Ca and C: N (0·64·4). Glutamine was the predominant o-phthalaldehyde-reactive aminocompound in both transport fluids with the next most abundantamino acids dependent on sap type and N-form. Together witharginine, -aminobutyric acid, which was found only in the xylemstream, was enhanced by NH+4compared to NO3 -nutrition suggestingthat glutamate metabolism was stimulated in the roots. Underlimiting N the amino acid concentrations in the transport fluidswere greater with NH+4 than with NO3. NO3 reduction occurredin both the root and shoot with the latter site predominatingover the entire N range (0-300 mol m3). Even though the compositionof nitrogenous solutes in the xylem was dependent on cultivarand N source, the composition of the phloem streams supplyingthe developing inflorescence was relatively unaffected. The data on the element composition of organs and phloem sapare interpreted to suggest that, in spite of the restrictedmobility of some elements such as B and Mn, a significant proportionof their total supply to developing sinks is carried in thephloem stream. Key words: Transport fluid composition, plant nutrition, phloem mobility. 相似文献
18.
Discontinuities at low moisture contents in the otherwise logarithmicrelations between seed longevity and seed moisture content (%,f. wt basis) in hermetic storage at 65 °C were detectedat 20% in groundnut (Arachis hypogaea L.), 3·5%in onion (Allium cepa L.), 4·5% in sugar beet (Beta vulgarisL.), 4·6% in barley (Hordeum vulgare L.), 5·3%in chickpea (Cicer arietinum L.) and wheat (Triticum aestinumL.), and 5·6% in cowpea [Vigna unguiculata (L.) Walp.].In contrast, the equilibrium relative humidity of seeds at thesevalues was similar, varying between 9·9% (onion and sugarbeet) and 11·5% (wheat). The mean value was 10·5%r.h. (s.e. 0.2). There was no significant (P > 0·05)effect of further reduction in seed moisture content below thesecritical values on longevity, except in wheat (P < 0·005),in which there was a further increase in longevity. In soyabean [Glycine max (L) Merrill], the logarithmic relation continueddown to the lowest moisture content investigated, 3·3%(11·4% equilibrium relative humidity). Above the criticalvalue, seed longevity in groundnut showed the least sensitivityto increase in percentage moisture content, while barley showedthe greatest, the values of the viability constant Cw (slopeof the negative logarithmic relation between longevity and moisture)being 4·089 (s.e. 0·278) and 5·966 (s.e.0·325), respectively. These differences in the valueof Cw among the eight crops were significant P < 0·005),whereas the relative sensitivity of seed longevity to changein equilibrium relative humidity above the critical moisturecontent did not differ significantly among the eight (P >0·10) and was equivalent to a doubling of longevity foreach 8·7% reduction in equilibrium relative humidity.Accordingly it is concluded that the relative effect of waterpotential on seed longevity can be considered to be the samefor these and probably also for many other orthodox species. Barley, chickpea, cowpea, groundnut, onion, soya bean, sugar beet, wheat, seed storage, seed longevity, seed moisture content, viability equation, water relations 相似文献
19.
Imsande, J. 1986. Nitrate-ammonium ratio required for pH homeostasisin hydroponically grown soybean.J. exp. Bot. 37: 341347. Plant acid-base homeostasis is achieved when the mmoles of hydroxylions produced in the plant equal the mmoles of protons. Reductionof nitrate to ammonia is the major source of hydroxyl ions whereasammonium uptake-assimilation and the metabolism of neutral sugarsto organic acids are the primary sources of protons. Soybean[Glycine max (L.) Merr plants were grown hydroponically on mediumsupplemented with 3·0 mol m3 nitrogen providedas various combinations of KNO3 and NH4NO3 Plant growth consumedessentially all available nitrogen in each case; however, onlyin flasks supplemented with approximately 1·8 minolesof KNO3 plus 0·6 mmole of NH4NO3 was the pH of the mediumunchanged. Thus, for every mmole of nitrogen assimilated, approximately0·6 mmole of dissociable protons must have been producedby the conversion of neutral sugars to carboxylic acids. Also,it was shown that a plant obtaining all of its nitrogen fromnitrate must neutralize or excrete approximately 0·5mmole of hydroxyl ion d1. Conversely, the plant derivingall of its nitrogen from dinitrogen must excrete or neutralizeat least 0·8 mmole of hydrogen ion d1 whereasthe plant deriving all of its nitrogen from aminonium must excreteor neutralize approximately 2·1 mmoles of hydrogen iond1. Nevertheless, plants grown on medium supplementedwith 2·4 mol m1 nitrate plus 0·6 mol m3ammonium did not achieve a higher growth rate than plants grownon 3·0 mol m3 nitrate. Key words: Glycine max, nitrogen fixation, nitrate utilization 相似文献
20.
The acidophilic alga Dunaliella acidophila exhibits optimalgrowth at pH 1. We have investigated the regulation of phosphateuptake by this alga using tracer techniques and by performingintracellular phosphate measurements under different growthconditions including phosphate limitation. In batch culturewith 2·2 mol m3 phosphate in the medium the uptakeof phosphate at micromolar phosphate concentrations followeda linear time dependence in the range of minutes and rates werein the range of 1 µmol phosphate mg1 chl h1,only. However, under discontinuous phosphate-limited growthconditions, tracer influx revealed a biphasic pattern at micromolarphosphate concentrations: An initial burst phase resulted ina 104-fold internal phosphate accumulation and levelled offafter about 10 s. A double reciprocal plot of the initial influxrates obtained for phosphate-limited and unlimited algae exhibitedMichaelis-Menten kinetics. Phosphate limitation caused a significantactivation of the maximum velocity of uptake, yielding Vmaxup to 1 mmol mg1 chl h1 as compared to valuesin the order of 50 µmol phosphate mg1 chl h1for the second phase (this magnitude is also representativefor non-limited batch cultures). Concomitantly the Michaelisconstant was altered from 4 mmol m3 to 0·7 mmolm3. The rapid uptake of phosphate was inhibited by arsenateand FCCP and was not stimulated by Na+. The pH dependence oftracer accumulation and measurements of the intracellular phosphatepool under different growth conditions indicate that at lowpH and low external phosphate concentrations the high protongradient present under these conditions is utilized for a H3PO4uptake or a H+/H2PO4 cotransport. However, when the externalphosphate concentration was increased to levels sufficientlyhigh for transport to be driven by the positive membrane potential(10 mol m3 phosphate), the pH dependence of phosphateuptake was more complex, but could be explained by the uptakeof H3PO4 or a H+/H2PO4-cotransport at low pH and a differenttype H2PO4-transport (with unknown type of ion coupling)at high pH-values. It is suggested that this flexible couplingof phosphate transport is of essential importance for the acidresistance of Dunaliella acidophila. Key words: Acid resistance, Dunaliella acidophila, phosphate cotransport, phosphate limitation, plasma membrane, sodium 相似文献