摘要:

ABSTRACTThe origin and subsequent evolution of life on Earth have taken place within an environment where a 1g gravitational field is omnipresent. Living organisms, at whatever stage in their evolution, have accommodated this variable in both their structure and their function. Systems have also evolved whereby gravitational accelerations are perceived by gravisensors and these, in turn, have led to responses that give particular spatial orientations to living processes. It is proposed that, the higher the evolutionary status of an organism, the more likely it is that it will possess multiple systems for gravisensing because evolution discards little that assists fitness and hence supplements with new gravisensing systems those which already existed within evolutionary older, less complex organisms. Moreover, in comparison with a single gravisensing system, a multiplicity of systems permits gravity to participate in a wider range of developmental programmes, such as taxes, morphisms and tropisms, through the action of different sensory mechanisms coupled to distinct signalling and response pathways. Whatever the precise mechanism of graviperception in any given set of conditions, all may transduce theg‐forcc by means of a membrane system. Transduction may involve the endoplasmic rcticulum and thence the plasma membran

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00606.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTIn isolated Elodea densa leaves, the relationships between H+extrusion (‐ΔH+), K+fluxes and membrane potential (Em) were investigated for two different conditions of activation of the ATP‐dependent H+pump. The ‘basal condition’ (darkness, no pump activator present) was characterized by low values of‐ΔH+and K+uptake (ΔK+), wide variability of the −ΔH+/ΔK+ratio, relatively low membrane polarization andEmvalues more positive than EK for external K+concentrations (|K+]oof up to 2mol m−3. A net K+uptake was seen already at [K+]obelow 1 mol m−3, suggesting that K+influx in this condition was a thermodynamically uphill process involving an active mechanism. When the H+pump was stimulated by fusicoccin (FC), by cytosol acidification, or by light (the ‘high polarization condition’), K+influx largely dominated K+and C−efflux, and the −ΔH+/ΔK+ratio approached unity. In the range 50 mmol m−3−5 mol m−3[K+]0, Emwas consistently more negative than EK. The curve of K+influx at [K+]0ranging from 50 to 5000mmol m−3fitted a monophasic, hyperbolic curve, with an apparent half saturation value = 0–2 mol m−3. Increasing |K+]0progressively depolarized Em, counteracting the strong hyperpolarizing effect of FC. The effects of K+in depolarizingEmwere well correlated with the effects on both K+influx and −ΔH+, suggesting a cause‐effect chain: K+0influx → depolarization → activation of H+extrusion. Cs+competitively inhibited K+influx much more strongly in the ‘high polarization’ than in the ‘basal’ condition (50% inhibition at [Cs+]/[K+]0ratios of 1:14 and 1:2, respectively) thus confirming the involvement of different K+uptake systems in the two conditions. These results suggest that in E. densa leaves two distinct modes of interactions rule the relationships between H+pump, membrane polarization and K+transport. At low membrane polarization, corresponding to a low state of activation of the PM H+‐ATPa

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00607.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTAbove‐ground nitrogen fluxes following a complete pruning of the neotropical agroforestry treeErythrina poeppi‐giana(Walpers) O.F. Cook (Leguminosae: Phaseoleae) were studied during pruning intervals of 26 and 23 weeks in the humid tropics of Costa Rica. The experiment included four clones and a half‐sib family of the species. The leaf‐level N fluxes were modelled as a function of leaf age, and were scaled to the canopy level on the basis of the leaf age distribution. The N content of young leaves increased exponentially, followed by relatively small changes at maturity. Slight net N retranslocation started at the middle of leaf life span, but a major N efflux occurred only a few days before leaf shedding. It was estimated that, depending on the tree source, 29‐44&of the total N accumulation in the above‐ground biomass occurred during 11 weeks after pruning (WAP), before initiation of nodulation. The nodule biomass peaked at the time leaf shedding started (15–17 WAP). Considerable rapid N efflux from the foliage was observed at this time, suggesting regulation of nodulation by a feedback from the foliage. The implications of the N economy ofE. poep‐pigianaon its management in agroforestry system

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00608.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe overall deuterium content of plant lipids has been investigated by isotope ratio mass spectrometry (IRMS), and the site‐specific natural isotope fractionation of hydrogen has been studied by2H‐NMR at natural abundance (SNIF‐NMR). An analytical strategy has been developed in order to exploit the isotopomeric composition determined in clusters associated with different chemical sites of one or several fatty acid components. The method, which combines spectrometric and chromatographic data, enables isotopic criteria to be directly derived from raw vegetable oils containing in general two saturated and two unsaturated fatty acids. These results provide new information on isotopic fractionation caused by biochemical, physiological and natural environmental effects. Some alternation in the molecular deuterium distribution has been detected which may be related to the mechanism of fatty acid elongation. The successive methylene groups introduced through malonyl CoA are the subjects of different kinetic isotope effects since one of them is exclusively derived from NADH whereas the other has a contribution from pyruvate. A discriminant analysis of the cluster isotopic parameters enables several kinds of botanical precursors to be distinguished. The authenticating performances can be improved by taking into account the influence of climatic effects related to the region in which the plant

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00609.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTWheat plants were cultivated under growth regimes combining two temperatures (ambient and 4°C above ambient temperature) with two concentrations or carbon dioxide (350 and 700 μmol mol) and two nitrogen fertilizer applications (high and low). The aim of this study was to define any changes in the acyl lipid composition of wheat grains which could result from alterations in the growth conditions. Qualitative and quantitative changes were observed in both non‐starch and starch lipid fractions. Temperature was by far the most influential growth factor, although interactions between all three growth conditions occurred, as confirmed by analysis of variance. Growth at elevated temperatures had the general effect of reducing the amounts of accumulated lipids, particularly non‐polar lipids (1322 nig fatty acids per 100 g fresh weight at ambient temperatures as opposed to 777 mg fatty acids per lOOg fresh weight at 4°C above ambient temperatures). There were changes in the proportions of the major non‐starch as well as the starch lipids. In the former category, non‐polar lipids (principally triacylglyc‐erols), the membrane glycosylglyccridcs and phos‐phatidylcholinc were the main constituents, whereas in the starch lipids, lysophosphatidylcholine and lysophos‐phatidylethanolamine represented over 70% of the total. Depending on the growth conditions, the percentages of lipids such as monogalactosyldiacylglycerol, digalactosyl‐diacylglycerol and phosphatidyleholine (non‐starch) or the starch lysophosphatidylethanolamine varied 2‐fold or more. Significant changes in the acyl composition of individual lipids were also observed, most often in the proportions of palmitate, oleate and linoleate. The observed alterations in wheat lipids arc likely to affect the properties of any flours derived from grain grown under cli

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00610.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTOn the basis of measurements or stand transpiration and microclimate, the bulk stomatal or bulk leaf conductance (gL) of a beech forest in northern Germany was calculated for periods in which leaves were fully expanded and the canopy was dry. This conductance depends strongly on light and humidity conditions above the forest. During periods with photosynthetic photon flux densitiesQ>1200 μmol m−2s−1,gLwas reduced from 1500mmol m−2s−1at a vapour pressure deficitD= 0.5kPa to 500 mmol m−2s−1atD= 2kPa. Light saturation ofgLwas not reached untilQ= 1200 μmol m−2s−1at lowD, or until even higherQat higherD. The dependence ofgL, onQandDwas described mathematically by a non‐linear equation that requires two empirical parameters. Values forgLas simulated by this equation provided a satisfactory agreement with independent porometer data collected on single leaves and scaled up to the canopy. A comparison of stomatal and aerodynamic conductances showed a strong coupling between the forest canopy and the atmosphere, indicating that transpiration of the beech forest is controlled ma

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00611.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTMutants of Pisum sativum L. with seeds containing low‐amylose starch were isolated by screening a population derived from chemically mutagenized material. In all of the mutant lines selected, the low‐amylose phenotype was caused by a recessive mutation at a single locus designated lam. In embryos of all but one mutant line, the 59 kDa granule‐bound starch synthase (GBSSI) was absent or greatly reduced in amount. The granule‐bound starch synthase activity in developing embryos of the mutants was reduced but not eliminated. These results provide further evidence that amylose synthesis is unique to GBSSI. Other granule‐bound isoforms of starch synthase cannot substitute for this protein in amylose synthesis. Examination of iodine‐stained starch granules from mutant embryos by light microscopy revealed large, blue‐staining cores surrounded by a pale‐staining periphery. In this respect, the low‐amylose mutants of pea differ from those of other species. The differential staining may indicate that the structure of amylopectin varies between the core and p

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00612.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTBiogenic emissions of halomethanes (CH3CI, CH3Br and CH3I) and methanethiol (CH3SH) are of major significance to atmospheric chemistry, but there is little information on such emissions from higher plants. We present evidence that plants can produce all these gases through an identical methyltransferase reaction. A survey of 118 herbaceous species, based on CH3I production by leaf discs supplied with Kl, detected the presence ofin vivohalide methyltransferase activity in 87 species. The activities ranged over nearly 4 orders of magnitude. Plants generally considered salt tolerant had relatively low activities, and salinization of three such species did not increase the activity. The highest activities were found in the family Brassicaceae. Leaf extracts ofBrassica oleraceacatalysed theS‐adenosyl‐L‐methioninc‐dependenl niethylalion of the halides I−, Br−and CI−to the respective halomethanes. In addition, the extract similarly methylated HS−(bisulphide) to CH3SH. These two types of enzyme activity (halide and bisulphide methyltransferase) were also present in all of the 20 species comprising a subsample that represented the range of CH3I emissions observed in the initial survey ofin vivoCH3I production ability, and in a marine red algaEndocladia muricata. Moreover, the two activities occurred in approximately the same ratio in all the higher plants tested. These findings highlight the potential of higher plants to contribute to the atmosphericbudget of halomethanes and melhanethiol. The halide and bisulphide methyltransferase activities may also provide a mechanism for the elimination of halide and HS−ions, both of which are known

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00613.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTWater deficit severely decreases maize (Zea maysL.) kernel growth; the effect is most pronounced in apical regions of ears. The capacity for accumulation of storage material in endosperms is thought to he partially determined by the extent of cell division and endoreduplication (post‐mitotic nuclear DNA synthesis). To gain a better understanding of the regulatory mechanisms involved, we have examined the effect of water deficit on cellular development during the post‐fertilization period. Greenhouse‐grown maize was subjected to water‐limited treatments during rapid cell division [from 1 to 10days after pollination (DAP)] or rapid endoreduplication (9 to 15 DAP). The number of nuclei and the nuclear DNA content were determined with flow cytometry. Water deficit from 1 to 10 DAP substantially decreased the rate of endosperm cell division in apical‐region kernels, but had little effect on middle‐region endosperms. Rewatcring did not allow cell division to recover in apical‐region endosperms. Water deficit from 9 to 15 DAP also decreased cell division in apical‐region endosperms. Endoreduplication was not affected by the late treatment in either region of the car, but was inhibited by the early treatment in the apical region. In particular, the proportion of nuclei entering higher DN A‐content size classes was reduced. We conclude that cell division is highly responsive to water deficit, whereas endoreduplication is less so. We also conclude that the reduced proportion of nuclei entering higher DNA‐content size classes during endoreduplication is indicative of multiple control points in the mitotic and endor

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00614.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe influence of NaCl and Na2SO4on growth of two maize cultivars (Zea mayscv. Pioneer 3906 and cv. Across 8023) differing in Na+uptake was investigated in two green‐house experiments. Na+treatment with different accompanying anions (Cl−/SO42−) showed that ion toxicity was caused by Na+. While shoot growth of the two cultivars was markedly affected by salt in comparison to the control during the first 2–3 weeks, there were only slight differences between the cultivars. The shoot Ca2+concentration was reduced in both cultivars, and the youngest leaves contained an even lower concentration compared with the rest of the shoot. During this first phase, Across 8023 tended to have higher concentrations of Ca2+than Pioneer 3906. The Na+‐excluding cultivar Pioneer 3906 showed continuous, although reduced, growth compared with the control, while the Na+concentration in the shoot decreased until flowering. Cultivar Across 8023 accumulated Na+until flowering: the reduction in the growth of stressed plants was greater than that for Pioneer 3906. Leaves of cultivar Across 8023 showed clear toxic symptoms, while those of the more salt‐tolerant cultivar Pioneer 3906 did not. It is concluded that Na+exclusion contributes to the salt toleran

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00615.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY