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101.
Light and dark assimilation of nitrate in plants 总被引:6,自引:3,他引:3
Abstract. Heterotrophic assimilation of nitrate in roots and leaves in darkness is closely linked with the oxidative pentose phosphate pathway. The supply of glucose-6-phosphate to roots and chloroplasts in leaves in darkness is essential for assimilation of nitrite into amino acids. When green leaves are exposed to light, the key enzyme, glucoses-phosphate dehydrogenase, is inhibited by reduction with thioredoxin. Hence the dark nitrate assimilatory pathway is inhibited under photoautotrophic conditions and replaced by regulatory reactions functioning in light. On account of direct photo-synthetic reduction of nitrite in chloroplasts and availability of excess NADH for nitrate reduclase, the rate of nitrate assimilation is extremely rapid in light. Under dark anaerobic conditions also nitrate is equally rapidly reduced to nitrite on account of abolition of competition for NADH between nitrate reductase and mitochondrial oxidation. 相似文献
102.
103.
104.
It has been proposed that many marine macroalgae are able to utilize HCO
3
–
for photosynthesis and growth, and that energy-dependent ion pumping is involved in this process. We have therefore studied the light-dependent alkalization of the surrounding medium by two species of marine macroscopic brown algae,Fucus serratus L. andLaminaria saccharina (L.) Lamour. with the aim of investigating the role of extracellular carbonic anhydrase (EC 4.2.1.1.) in the assimilation of inorganic carbon from the seawater medium. In particular, the influence of membrane-impermeable or slowly permeable carbonic-anhydrase inhibitors on the rate of alkalization of the seawater has been investigated. Inhibition of the alkalization rate occurred in both species at an alkaline pH (pH 8.0) but no inhibition was observed at an acidic pH (pH 6.0). The alkalization was found to be light-dependent and inhibited by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea and, thus, correlated with photosynthesis. Alkalization by macroalgae has previously been shown to be proportional to inorganiccarbon uptake. We suggest that alkalization of the medium at alkaline pH in both of the species examined is mainly the consequence of an extracellular reaction. The reaction is catalyzed by extracellular carbonic anhydrase which converts HCO
3
–
to OH– and CO2; CO2 is then taken up through the plasmalemma. However, we do not exclude the involvement of other mechanisms of inorganic-carbon uptake.Abbreviations AZ
acetazolamide
- CA
carbonic anhydrase
- CAext
extracellular carbonic anhydrase
- Ci
inorganic carbon
- DBS
dextran-bound sulfonamide
- DCMU
3-(3,4-dichloro-phenyl)-1,1-dimethylurea
- PPFD
photosynthetic photon flux density
This study was carried out with financial support by SAREC (Swedish Agency for Research Cooperation with Developing Countries), Carl Trygger's Fund for Scientific Research (Sweden), SJFR (Swedish Council for Forestry and Agricultural Research) and CICYT (Spain). Z. Ramazanov is an invited professor of Ministerio de Educación y Ciencia, Spain. 相似文献
105.
The symbiotic root nodule, an organ formed on leguminous plants, is a product of successful interactions between the host plant and the soil bacteria, Rhizobium spp. Plant hormones play an important role in the genesis of this organ. The hormonal balance appears to be modulated by the signals produced by bacteria. Many host genes induced during nodule organogenesis and the symbiotic state have been identified and characterized from several legumes. These genes encode nodule-specific proteins (nodulins) which perform diverse functions in root nodule development and metabolism. Formation of a subcellular compartment housing the bacteria is essential to sustain the symbiotic state, and several nodulins are involved in maintaining the integrity and function of this compartment. The bacteroid enclosed in the perbacteroid membrane behaves as an 'organelle,'completely dependent on the host for all its requirements for carbon, nitrogen and other essential elements. Thus it seems likely that the nodulins in the peribacteroid membrane perform specific transport functions. While the function of a few other nodulins is known (e.g. nodulin-100, nodulin-35), a group of uncharacterized nodulins exists in soybean root nodules. These nodulins share structural similarities and seem to have been derived from a common ancestor. Induction of nodulin genes occurs prior to and independent of nitrogen fixation, and thus is a prelude to symbiosis. Although some of the early nodulin genes are induced prior to or during infection, induction of late nodulins requires endocytotic release of bacteria. 相似文献
106.
Immunocytolocalization of glutamine synthetase in mesophyll and phloem of leaves ofSolanum tuberosum L. 总被引:1,自引:0,他引:1
Summary Localization of glutamine synthetase inSolanum tuberosum leaves was investigated by techniques of Western tissue printing and immunogold electron microscopy. Anti-GS antibodies used in immunolocalization recognize two peptides (45 kDa and 42 kDa) on Western blots. Antibody stained tissue prints on nitrocellulose membranes allowed low resolution localization of GS. Immunostaining was most evident in the adaxial phloem of the leaf midribs and petiole veins. High-resolution localization of glutamine synthetase by immunogold electron microscopy revealed that this enzyme occurs in both the chloroplasts and the cytosol ofS. tuberosum leaf cells. However, GS was specifically associated with the chloroplasts of mesophyll cells and with the cytoplasm of phloem companion cells. The evidence for cell-specific localization of chloroplast and cytosolic GS presented here agrees with the recently reported cell-specific pattern of expression of GUS reporter gene, directed by promoters for chloroplast and cytosolic GS form in tobacco transgenic plants. These data provide additional clues to the interpretation of the functional role of these different isoenzymes and its relationship with their specific localization.Abbreviations BSA
bovine serum albumin
- EM
electron microscope
- GOGAT
glutamate synthase
- GS
glutamine synthetase
- GUS
-glucuronidase
- IgG
immunoglobulin
- PBS
phosphate buffer saline
- SDS-PAGE
sodium dodecyl sulphate-polyacrylamide gel electrophoresis 相似文献
107.
Seasonal and spatial patterns of S,Ca, and N dynamics of a Northern Hardwood forest ecosystem 总被引:1,自引:1,他引:0
Seasonal dynamics of S, Ca and N were examined at the Huntington Forest, a northern hardwood ecosystem in the central Adirondacks
of New York for a period of 34 months (1985–1988). Solute concentrations and fluxes in bulk precipitation, throughfall (TF)
and leachates from the forest floor, E horizon and B horizon were quantified. Both above and below-ground elemental fluxes
mediated by vegetation (e.g. uptake, litter inputs, and fine roots production) were also determined. The roles of abiotic
and biotic processes were ascertained based on both changes in solute concentrations through the strata of the ecosystem as
well as differences between dormant and growing seasons. Concentrations of SO4
2−, NO3
−, NH4
+ and Ca2+ were greater in TF than precipitation. Forest floor leachates had greater concentrations of SO4
2−, NO3
− + NH4
+ and Ca2+ (9, 6 and 77 μeq L−1, respectively) than TF. There were differences in concentrations of ions in leachates from the forest floor between the dormant
and growing seasons presumably due to vegetation uptake and microbial immobilization. Concentrations and fluxes of NO3
− and NH; were greatest in early spring followed by a rapid decline which coincided with a demand for N by vegetation in late
spring. Vegetation uptake (44.7 kg N ha−1 yr−1 ) could account for the low leaching rates of N03
−. Within the mineral soil, changes with soil depth and the absence of seasonal patterns suggest that cation exchange (Ca+) or anion sorption (SO4
2−) are primarily responsible for regulating solute concentrations. The increase in SO4
2− concentration after leachates passed through the mineral soil may be attributed to desorption of sulfate that was adsorbed
during an earlier period when SO4
2− concentrations would have been greater due to elevated S inputs. 相似文献
108.
Sulfate reduction and S-oxidation in a moorland pool sediment 总被引:3,自引:2,他引:1
In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO4
2– reduction rates in the sediment, (2) depletion of SO4
2– in the overlying water column and (3) release of35S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO4
2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core35SO4
2– injection. Rates of SO4
2– consumption in the overlying water were estimated by changes in SO4
2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m–2 d–1. Rates of SO4
2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m–2 d–1 (November) to 0.43–1.81 mmol m–2 d–1 (July, August and April). Maximum rates of oxidation to SO4
2– in July 1990 estimated by combination of SO4
2– reduction rates and rates of in situ SO4
2– uptake in the enclosed water column were 10.3 and 10.5 mmol m–2 d–1 at an organic rich and at a sandy site respectively.Experiments with35S2– and35SO4
2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO4
2– and (2) the presence of mainly non SO4
2–-S derived from reduced S transported from the sediment into the overlying water. A35S2– tracer experiment showed that about 7% of35S2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author 相似文献
109.
Superconducting vibronic interaction in the vibronic superconductivity motif has been studied in the Hückel framework for (AB)
N
chain systems. Within the on-site and nearest-neighbor approximation a new vibronic constant, /L, has been introduced, of which the importance has been discussed. The effect of the vibronic operator, , has also been studied. It is also concluded that the size-dependence of the superconducting vibronic interaction also exists in the (AB)
N
chain systems.On leave from the Changchun Institute of Applied Chemistry, Academia Sinica, Changchun, P. R. China, as an STA fellowship awardee hosted by the Institute of Physical and Chemical Research of Japan. 相似文献
110.
Non-resistant but tolerant cv. Cara and non-resistant but relatively intolerant cv. Pentland Dell were grown in split plots encompassing a range of population densities of potato cyst nematode, Globodera pallida. Light interception and its efficiency of conversion were estimated by regular ground cover measurements and plant harvests. It was concluded that increasing levels of infestation with G. pallida only slightly decreased the efficiency of utilisation of intercepted radiation. Heavy infestation of G. pallida initially decreased the top growth and light interception of both cultivars by similar proportions, but in later harvests, this adverse effect markedly decreased for Cara whereas it slightly increased for Pentland Dell. This difference was due to the heavily infested Cara eventually achieving and maintaining 100% ground cover whereas the equivalent Pentland Dell never exceeded 75% ground cover. Consequently, final tuber yields were decreased much more for Pentland Dell than for Cara though the decreases in tuber yield were less than those for top growth. The importance of nematode effects on top growth, and hence on light interception, with regard to both yield losses and tolerance differences, were clearly demonstrated. Both linear and logarithmic models were used to describe the relationship between the initial population density of G. pallida and yield, and the implications of differences in tolerance on the parameters in the logarithmic model are discussed. 相似文献