摘要:

Carbon and nitrogen partitioning was examined in a wild‐type and a nitrate reductase‐deficient mutant (A317) ofPisum sativumL. (ev. Juneau), effectively inoculated with two strains ofRhizobium leguminosarum(128C23 and 128C54) and grown hydroponically in medium without nitrogen for 21 days, followed by a further 7 days in medium without and with 5 mM NH4NO3. In wild‐type symbioses the application of NH4NO3significantly reduced nodule growth, nitrogenase (EC 1.7.99.2) activity, nodule carbohydrates (soluble sugars and starch) and allocation of [14C]‐labelled (NO3−, NH4+, amino acids) in roots. In nodules, there was a decline in amino acids together with an increase in inorganic nitrogen concentration. In contrast, symbioses involving A317 exhibited no change in nitrogenase activity or nodule carbohydrates, and the concentrations of all nitrogenous solutes measured (including asparagine) in roots and nodules were enhanced. Photosynthate allocation to the nodule was reduced in the 128C23 symbiosis. Nitrite accumulation was not detected in any case. These data cannot be wholly explained by either the carbohydrate deprivation hypothesis or the nitrite hypothesis for the inhibition of symbiotic nitrogen fixation by combined nitrogen. Our result with A317 also provided evidence against the hypothesis that NO3−and NH4+or its assimilation products exert a direct effect on nitrogenase activity. It is concluded that more than one legume host andRhizobiumstrain must be studied before generalizations aboutRhizobium/legume interactio

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02023.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A mitochondrial serine hydroxymethyltransferase (EC 2.1.2.1) has for the first time been purified close to homogeneity from a photosynthetically active tissue, spinach (Spinacea oleraceaL. cv Viking II) leaves. The specific activity of the enzyme was 7.8 μmol (mg protein)−1min−1using L‐serine as substrate. The enzyme was stable for at least 8 weeks at 4°C in the presence of folate. The pH optimum was at pH 8.5 where the enzyme had a Kmfor L‐serine of 0.9 mM. Carboxymethoxylamine was a strong competitive inhibitor with a K1of 1.4 μM. An absorption spectrum taken of the enzyme in the presence of glycine and tetrahydrofolate showed a peak at 492 nm, probably originating from a substrate‐enzyme complex. The molecular weight obtained by gel filtration was 209 kDa. Sodium dodecyl sulphate‐polyacrylamide gel electrophoresis of the purified enzyme showed that the apparent molecular weight of the subunit was 53 kDa, indicating

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02024.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

It was postulated that the release of lateral buds from apical dominance is triggered by the immediate increase in apoplastic water potential (hydrostatic pressure) that is produced by shoot decapitation and that is rapidly transmitted throughout the plant. In experiments conducted to test this hypothesis the use of a strain gauge transducer capable of measuring bud growth with an accuracy of ± 0.1 μm, showed that growth of the inhibited lateral bud at the primary leaf node ofPhaseolus vulgaris(L.) ev. Canadian Wonder was initiated within 1 to 5 s following shoot decapitation or excision of the primary leaves. When only the apical bud was excised the lateral bud showed a brief, transitory growth response of ca 1 min duration, but the axillary buds of the first and second trifoliate leaves were released from inhibition. Decapitation of the shoot just below the first trifoliate leaf induced a lateral bud response characterized by three distinct stages: a) a rapid initial growth response with a mean duration of 4.9 min b) a period of arrested growth, which varied in duration from 2 min to 4 h and c) the subsequent resumption of growth.Excision of both primary leaves induced a rapid but transitory bud response of considerably greater duration than that induced by apical bud excision. Excision of the primary leaves prior to decapitation of the shoot eliminated the phase of arrested growth, which characterized the bud response to decapitation of the intact plant. The rapidity of the bud response to both shoot decapitation and leaf excision and the interaction between the effect of these two treatments are consistent with the hypothesis that competition for water plays a major role in the correlative inhibition of lateral bud

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02025.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Plasma membrane ATPase from the mediterranean halophytePlantago crassifoliaForskal was analysed in the native and solubilized state. The enzyme revealed a broad pH optimum at 6.3 when analysed in plasma membrane preparations from roots. A further purified preparation of leaf plasma membrane ATPase was obtained by a three‐step solubilization method. Final solubilization of the enzyme was achieved with 1% lysophosphatidylcholine. This enzyme showed a narrow pH optimum at 6.3, inhibition by vanadate, fluoride and N,N′‐dicyclohexylcarbodiimide and a high specificity for ATP. The preparations contained a major polypeptide of 107 kDa. None of the parameters analysed in this enzyme changed upon transfer to saline conditions, although the leaves accumulated Na+and Cl−and an enhanced formation of the compatible organic osmoticum, sorbitol, was detected. It is concluded that at least in this halophyte, the plasma membrane ATPase undergoes no changes during the physiological adaptation of the plant to a saline envi

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02026.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

When suspension‐cultured cells ofAtropa belladonnaL. were in late growth phase, phenylalanine, one of the early precursors of atropine, was taken up mainly by diffusion without carrier but also actively via mediated transport. The uptake capacity of different callus lines varied from 0.4 to 1.9 μol (g fresh weight)−1h−1with an optimum pH at 4.5 or 5.0, depending on the callus line, 2,4‐Dinitrophenol (DNP) and KCN inhibited about 35–45% of the total uptake in all tested callus lines, so that a part of the uptke was dependent on metabolic energy.The rate of phenylalanine uptake was fastest from 2 to 7 days after the start of the suspension culture. The increase was from 50 to 300%, depending on the cell line. The enhancement was mainly due to increased mediated uptake and could be inhibited by cycloheximide during the first days of the suspension culture. Glutamine, added to the nutrient medium, also prevented the increase. The inhibition caused by glutamine together with cycloheximide was not additive. Obviously, glutamine did not directly affect the carrier, but possibly repressed its synthesis. When cells entered the stationary phase, the total uptake began to decrease, and most of it was non‐mediated. The suspension cultures ofA. belladonnahad only limited capacity to regulate the transport of phenylalanine into the cells at this pha

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02027.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Fusicoccin was evaluated for its effects on brassinosteroid (BR), indole‐3‐acetic acid (IAA) and BR + IAA‐induced ethylene, 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and ACC‐synthase production by etiolated mung bean (Vigna radiataL. Rwilez cv. Berken) hypocotyl segments. Fusicoccin inhibition of ethylene and ACC production induced by 2 μMBR started at concentrations as low as 0.05 μM. Maximum inhibition occurred at a 1 μMconcentration with no further inhibition at higher concentrations tested. Fusicoccin (1 μM) was effective in the inhibition of BR‐induced ethylene, ACC and ACC‐synthase production at low and high concentrations of BR.Fusicoccin at concentrations as high as 2 μMhad no effect on ethylene and ACC production promoted by low concentrations of IAA (1 to 10 μM). When higher concentrations (100–1000 μM) of IAA were used, fusicoccin (1 μM) had an inhibitory effect on ethylene and ACC production. Interestingly, fusicoccin (1 μM) had little or no effect on ACC‐synthase promoted by high concentrations of IAA (1000 μM).When BR and IAA were used in combination, fusicoccin inhibited ethylene and ACC production at concentrations as low as 0.05 μMwith maximum inhibition occurring at 0.5 μM. At a 1 μMconcentration, fusicoccin was effective in inhibiting the synergistic stimulation of A

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02028.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Net CO2exchange rates (CERs) were measured in seedlings of two loblotly pine (Pinus taedaL.) families following 6‐ or 13‐week exposures to ozone (charcoalfiltered or ambient air + O3) and acid rain treatments (pH 3.3, 4.5 and 5.2). Ozone exposures (14 or 170 nl l−1) were made in open‐top chambers, and in continously stirred tank reactors (14, 160 or 320 nl l−1) located in the field and laboratory, respectively. The CERs of whole shoots were measured in an open infrared gas analysis system at 6 levels of photosynthetic photon flux density (0, 33, 60, 410, 800 and 1660 μmol m−2s−1). Treatment effects were not consistent between field‐ and laboratory‐exposed seedlings. Ozone‐treated field seedlings exhibited statistically significant reductions in light‐saturated CER of 12.5 and 25% when measured at 6 and 13 weeks, respectively. Laboratory seedlings exhibited mixed responses to O3, with one family showing reduced CER only after 6 weeks of O3exposure and the other only after 13 weeks (O3>160 nl l−1for both). After 13 weeks of exposure, pH 3.3, and 4.5 rain treatments enhanced light‐saturated CER by an average of 52% over that observed in seedlings exposed to the pH 5.2 treatment. Enhanced CERs due to acid rain were of the same magnitude (3–5 μmol CO2g−1s−1) as ozone‐induced CER reductions. No differences in dark respiration were detected between treatments. Although ozone and acid rain treatments altered seedling CER, the differences were not translated into altered final plant dry weigh

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02029.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Cleared maize (Zea maysL. cv. LG 11) root homogenates were prepared and layered on the top of sucrose step gradients (10, 35 and 45%). The ATP‐ and pyrophosphate (PPi)‐dependent proton‐pumping activities were recovered almost completely at the 10%/35% interface, corresponding to the microsomal fraction (Golgi, tonoplast and endoplasmic reticulum). The PPi‐dependent proton pump was characterized by the fluorescence quenching of quenching of quinacrine. The pH optimum was 7 to 8. The H+‐PPase was Mg2+‐dependent and the Kmfor PPi(in the presence of 3 mMMgSO4) was 28 μM. The pump was electrogenic, K+‐dependent and a permeant anion was necessary to dissipate the membrane potential (NO3−= I−>Br−>Cl−). No activity was detected in the presence of electroneutral proton inonophores or, when valinomycin was added, with electrogenic ionophores. The H+‐PPase was insensitive to vanadate, oligomycin and molybdate. ‐Diethylstilbestrol (DES) and N,N′‐dicyclohexylcarbodiimide (DCCD) were

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02030.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Chloride concentrations within individual chloroplasts, the adjacent cytoplasm and nearby vacuoles of spinach mesophyll cells (Spinacea oleraceaL. cv. Hybrid 102) were determined by means of electron probe X‐ray microanalysis in the cleavage plane of quench frozen tissue, which was maintained at liquid nitrogen temperatures. The accuracy of quantitative data obtained with this technique is greatly improved by the adoption of a peak to background ratio method and use of carbon slurry standards, which mimic the quench frozen tissue and its X‐ray fluorescence.Chloroplasts were incapable of maintaining relatively high levels of Cl−under conditions of low Cl−availability (zero Cl−or 20 μMCl−in nutrient solution), and under conditions of Cl−stress (100 or 200 mMCl−) chloroplasts had only a limited capacity to maintain a Cl−concentration at a level below that of the cytoplasm and vacuole. However, under conditions of Cl−stress the concentration of Cl−in cytoplasm immediately adjacent to chloroplasts was substantially higher than in the chloroplasts or more distant cytoplasm. Thus, Cl−levels in chloroplasts are apparently not as tightly regulated as was suggested by estimates of Cl−concentration based on aqueous isolation of chloroplasts.Levels of S in chloroplasts were relatively high (equivalent to 40–60 mMSO42−in S standards) and constant for all treatments, with the possible exception of lower S levels in chloroplasts of leaves approaching premature senescence as a result of salt stress. It is implied that the stability of the S‐content results largely from its presence in macromolecular components of chlorop

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02031.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Reactions regulating seed dormancy can proceed at water contents which are probably too low to permit metabolic activity. The loss of dormancy via afterripening of red rice. (Oryza sativaL.) seeds was examined as a representative case. Equilibration of seeds to various moisture contents showed that afterripening was most rapid at 6–14% moisture content (dry weight basis). Afterripening did not occur at>18% moisture content and was severely inhibited at<5% moisture content. Seed viability was greater than 95% for all treatments. Utilization of moisture isotherms to calculate water‐binding enthalpy values identified the optimal afterripening range as approximately the boundary between water‐binding region 1 and region 2. From these findings, it is suggested that afterripening may involve some oxidative reactions which are inhibited at lower water contents by the rising free‐energy and at the higher side by metabolic re

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb02032.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY