共查询到20条相似文献,搜索用时 31 毫秒
1.
Schmidt-Wellenburg CA Biebach H Daan S Visser GH 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(3):327-337
Many bird species steeply increase their body mass prior to migration. These fuel stores are necessary for long flights and
to overcome ecological barriers. The elevated body mass is generally thought to cause higher flight costs. The relationship
between mass and costs has been investigated mostly by interspecific comparison and by aerodynamic modelling. Here, we directly
measured the energy expenditure of Barn Swallows (Hirundo rustica) flying unrestrained and repeatedly for several hours in a wind tunnel with natural variations in body mass. Energy expenditure
during flight (e
f, in W) was found to increase with body mass (m, in g) following the equation e
f = 0.38 × m
0.58. The scaling exponent (0.58) is smaller than assumed in aerodynamic calculations and than observed in most interspecific
allometric comparisons. Wing beat frequency (WBF, in Hz) also scales with body mass (WBF = 2.4 × m
0.38), but at a smaller exponent. Hence there is no linear relationship between e
f and WBF. We propose that spontaneous changes in body mass during endurance flights are accompanied by physiological changes
(such as enhanced oxygen and nutrient supply of the muscles) that are not taken into consideration in standard aerodynamic
calculations, and also do not appear in interspecific comparison. 相似文献
2.
Binding equations for interacting systems comprising multivalent acceptor and bivalent ligand: application to antigen-antibody systems 总被引:1,自引:0,他引:1
Consideration is given to the reversible interaction of a bivalent ligand, B, with a multivalent acceptor, A (possessing f reactive sites) which leads to the formation of a series of complexes, AiBj, comprising networks of alternating acceptor and ligand molecules. A binding equation is derived on the basis of a site association constant, k, defined in terms of reacted site probability functions. This equation, which relates the binding function, r (the moles of ligand bound per mole of acceptor) to the concentration of unbound ligand, mb, is used to show that plots of r vs. 2kmB constructed with fixed but different values of intersect at the point () where the extent of reaction and the concentrations of those complexes for which attain maximal values. Corresponding Scatchard plots are shown by numerical example to be non-linear, their second derivative being positive for all r. It follows that such deviations from linearity cannot be taken alone as evidence for site heterogeneity in cross-linking systems. The binding equation obtained directly is shown to be identical with that obtained with f = 2 by summation procedures involving the general expression for concentrations of complexes, mAiBj, formulated in terms of appropriate statistical factors. In this way, previous findings on precipitation and gel formation in cross-linking systems are correlated with the present development of binding theory. 相似文献
3.
A. Hedenström 《Animal behaviour》2003,66(4):631-636
Optimal migration theory depends to a large extent on the range equation, that is, a function relating potential distance moved to fuel load. Such range equations derived from aerodynamic principles exist for birds. I derive an analogous range equation for animals that run based on biomechanical principles. The range for animals that run isY∞ ln(1+f), where f is the relative fuel load at departure and relates the mass at departure (m) to the lean mass (m0) as m=(1+f) m0. Predictions pertaining to migration decisions, such as optimal stopover duration, fuel load and detours around barriers, can thereby be made for animals other than birds. I hope this paper will stimulate further experimental tests regarding migration decisions in suitable animal systems. 相似文献
4.
Two isoperoxidases (Af and Cn) from the medium of tobacco tissue suspension culture WR-132 grown in darkness have been purified to apparent homogeneity and partially characterized. Cn and Af have MWs of ca 30 000 and 54 000, respectively. Af has ca 5.1% carbohydrate, but none could be detected in Cn. Both isoperoxidases appear to follow simple Michaelis-Menten kinetics with respect to guaiacol as the substrate. The Kms for guaiacol are 4 and 13.3 mM for Af and Cn, respectively, while both isoperoxidases have a pH optimum at 6.5. Cn, is dissimilar to other isoperoxidases from tobacco tissue cultures, but Af is very similar to isoperoxidase A3 from W-38 tobacco tissue culture. 相似文献
5.
A.Scott Goustin 《Developmental biology》1981,87(1):163-175
This report presents an analysis of histone gene expression in the cleaving embryo of the sea urchin, Strongylocentrotus purpuratus, with emphasis on whether the regulatory site(s) in the pathway of gene expression change as development proceeds. The analysis focuses on the equation, , where = the absolute rate of histone synthesis; M = the mole quantity of histone messenger RNA; f = the fraction of histone mRNA in polysomes; n = the polysome size; and = the rate of elongation of nascent histone polypeptide chains. The embryo solves this rate equation differently at different times. Measurements were made (at 15°C) of absolute rates of histone synthesis (). The rate of histone synthesis increases at least 48-fold during the first 6 hr after fertilization from less than 0.5 to 24 pg embryo?1 hr?1; in the period from 6 to 12 hr, this rate rises to 182 pg embryo?1 hr?1, an additional 7.7-fold rise, resulting in an overall increase of 370-fold between the 1-cell and 200-cell stage. The fraction of newly synthesized (zygotic) histone messenger RNA that partitions into polysomes (fzygotic) has also been measured during the first 12 hr of development. This fraction increases from 0.2 in the 2-hr embryo to 0.8 in the 6-hr embryo (16-cell stage), increasing slowly thereafter to near unity by 12 hr. The size of histone-synthesizing polysomes (n) does not change substantially over the 12-hr interval, remaining constant at a weighted mean of 5 ribosomes per polysome (range 3 to 7). Utilizing the data on fzygotic and , the rate of elongation of nascent histone polypeptide chains () during the first 6 hr of development was estimated; remains constant at 1.11 codons per second. This calculated value is in fair agreement with a direct measurement of histone peptide elongation rate in the 12-hr embryo. It is proposed that histone gene expression in cleaving sea urchin embryos be divided into two phases, distinguished on the basis of their pivotal translational parameters: Phase I (0–6 hr), during which f is rate determining, and Phase II (6 hr on), during which M is the rate-determining parameter. 相似文献
6.
Dale M. Kikuchi Yutaka Watanuki Nobuhiko Sato Kenji Hoshina Akinori Takahashi Yuuki Y. Watanabe 《Journal of avian biology》2015,46(4):406-411
Alcids propel themselves by flapping wings in air and water that have vastly different densities. We hypothesized that alcids change wing kinematics and maintain Strouhal numbers (St = fA/U, where f is wingbeat frequency, A is the wingbeat amplitude, and U is forward speed) within a certain range, to achieve efficient locomotion during both flying and swimming. We used acceleration and GPS loggers to measure the wingbeat frequency and forward speed of free‐ranging rhinoceros auklets Cerorhinca monocerata during both flying and swimming. We also measured wingbeat amplitude from video footage taken in the wild. On average, wingbeat frequency, forward speed, and wingbeat amplitude were 8.9 Hz, 15.3 m s?1, and 0.39 m, respectively, during flying, and 2.6 Hz, 1.3 m s?1, and 0.18 m, respectively, during swimming. The smaller wingbeat amplitude during swimming was achieved by partially folding the wings, while maintaining the dorso‐ventral wingbeat angle. Mean St was 0.23 during flying and 0.36 during swimming. The higher St value for swimming might be related to the higher thrust force required for propulsion in water. Our results suggest that rhinoceros auklets maintain St for both flying and swimming within the range (0.2–0.4) that propulsive efficiency is known to be high and St in both flying specialists and swimming specialists are known to converge. 相似文献
7.
Mária Megyeri Péter Mikó András Farkas Márta Molnár-Láng István Molnár 《Journal of applied genetics》2017,58(1):67-70
The cytomolecular discrimination of the Am- and A-genome chromosomes facilitates the selection of wheat-Triticum monococcum introgression lines. Fluorescence in situ hybridisation (FISH) with the commonly used DNA probes Afa family, 18S rDNA and pSc119.2 showed that the more complex hybridisation pattern obtained in T. monococcum relative to bread wheat made it possible to differentiate the Am and A chromosomes within homoeologous groups 1, 4 and 5. In order to provide additional chromosomal landmarks to discriminate the Am and A chromosomes, the microsatellite repeats (GAA)n, (CAG)n, (CAC)n, (AAC)n, (AGG)n and (ACT)n were tested as FISH probes. These showed that T. monococcum chromosomes have fewer, generally weaker, simple sequence repeat (SSR) signals than the A-genome chromosomes of hexaploid wheat. A differential hybridisation pattern was observed on 6Am and 6A chromosomes with all the SSR probes tested except for the (ACT)n probe. The 2Am and 2A chromosomes were differentiated by the signals given by the (GAA)n, (CAG)n and (AAC)n repeats, while only (GAA)n discriminated the chromosomes 3Am and 3A. Chromosomes 7Am and 7A could be differentiated by the lack of (GAA)n and (AGG)n signals on 7A. As potential landmarks for identifying the Am chromosomes, SSR repeats will facilitate the introgression of T. monococcum chromatin into wheat. 相似文献
8.
The diversity of dinucleotide sequences at the 5′ ends of vaccinia virus mRNA's was determined by a two-dimensional electrophoresis procedure. RNA labeled with S-adenosyl[methyl-3H]methionine was synthesized in vitro by enzymes present in vaccinia virus cores. The RNA, ending in m7G(5′)pppNmpN−, was β-eliminated and treated with alkaline phosphatase. After digestion with RNases T2, T1, and A, all eight possible dinucleotides containing Gm and Am were identified. They are, in decreasing order of abundance: GmpUp (22%), AmpCp (18%), GmpAp (16%), GmpCp (15%), AmpAp (11%), AmpUp (10%), AmpGp (7%), and GmpGp (2%). 相似文献
9.
Theory is presented relating to the reversible interaction of an f-valent acceptor, A, with a bivalent ligand, B, which leads to the formation of a series of complexes comprising networks of alternating A and B molecules. An explicit expression is derived for the overall extent of reaction in terms of the total molar concentrations of reactants and , the valency of the acceptor and the site-binding constant, k, governing the equilibria. It is shown by differentiation of this expression holding (or ) fixed that relations are available for the independent evaluation of f and k from a combination of precipitin and radioimmunoassay experiments. Moreover, it is established that dilution with solvent ( fixed) cannot lead to the appearance of a precipitate with this type of crosslinking system. The latter observation forms the background for the development of theory pertaining to the joint operation of ligand dimerization, 2B?B2, and crosslinking of the multivalent acceptor with bivalent B2. The theoretical examination of this system is developed in terms of site-probability functions and involves the delineation of unique solutions for the extent of crosslinking reaction aided by the definition of the extent of binding in defined limits. It is shown with the use of numerical examples that the system involving self-associating ligand may result in the appearance of a precipitate on dilution with solvent and the conditions for the operation of this phenomenon are elucidated. It is noted that other types of ligand self-interaction may lead to similar effects in crosslinking systems, and the general principles emerging from this study are discussed in terms of systems in which antibody ligands are known to be involved in association reactions or are suspected to be so involved on the basis of precipitation effects observed on dilution with solvent. 相似文献
10.
George L. Wolff 《Genetics》1978,88(3):529-539
The results of extensive breeding experiments indicate that the phenotypic differentiation of embryos carrying the viable yellow, A vy, or mottled, am, mutations is influenced to a major extent by the agouti locus genotype and the strain genome of the dam. The Avy/a and am/a genotypes are each expressed in a spectrum of coat color phenotypes. These can be grouped into two classes, mottled and pseudoagouti.—In a reciprocal cross of C57BL/6JNIcrWf and AM/Wf-am/am mice, 29.5% of the offspring of C57BL/6 dams were of the pseudoagouti phenotype, whereas no pseudoagouti offspring were produced by AM strain dams.—Mottled yellow Avy/a mice become obese and tumor formation is enhanced in these mice in comparison with the lean pseudoagouti Avy/a siblings.—In two different reciprocal crosses using four different inbred strains, the proportion of pseudoagouti Avy/a offspring differed according to the strain of the dam. Regardless of strain, mottled yellow A vy/a dams produced significantly fewer pseudoagouti A vy/a offspring than did black a/a dams.—The data suggest that metabolic differentiation of Avy/a zygotes into phenotypic classes with different susceptibilities to obesity and tumor formation is influenced to a considerable degree by the metabolic characteristics of the oviductal and uterine environment of the dam. 相似文献
11.
《Journal of biochemical and biophysical methods》1995,30(2-3):113-131
A new approach has been developed to monitor protein folding by utilizing osmotic pressure and a range of salt concentrations in a well characterized protein, bovine serum albumin (BSA). It is hypothesized that both the ‘effective’ osmotic molecular weight, Ae, and the solute/solvent interaction parameter, I, in the empirical relation [1] can be used as measures of protein folding. I is a measure of solvent perturbed by the solute and is thought to depend directly upon the solvent accessible surface area (ASA). It is reasoned that larger solvent accessible surface area of an unfolded or denatured protein should perturb more water and produce larger I-values. Thus I-values allow calculation of a unfolded protein fraction, fua, due to changes in relative solvent accessible surface area. It has been observed that Ae decreases for filamentous, denatured proteins due to segmental motion of the molecule [2]. This allows calculation of unfolded protein fraction from the effective molecular weight, fum. Colloid osmotic pressure of BSA was measured in a range of salt concentrations at 25°C, and pH = 7 (above the isoelectric point of BSA at pH = 5.4). Both S and I were used to monitor protein folding as the salt concentration was varied. In general, larger and variable I-values and smaller Ae were observed at salt concentrations less than 50 mmolal NaCl (Imax = 8.9), while constant I = 4.1 and Ae = 66,500 were observed above 50 mmolal NaCl. The two expressions for fractional unfolding (fua and fum) are in general agreement. Small differences in the parameters below 50 mmolal salt concentration are explained with well known shifts in the relative amounts of α-helix, β-sheet and random coil in denatured BSA. The relative amounts of these shifts agree with predictions in the literature attributed to continuous BSA expansion rather than an ‘all-or-none’ conversion. 相似文献
12.
Dan Yu Nan Dai Eric J. Wolf Ivan R. Corrêa Jr. Jujun Zhou Tao Wu Robert M. Blumenthal Xing Zhang Xiaodong Cheng 《The Journal of biological chemistry》2022,298(4)
The phosphorylated RNA polymerase II CTD interacting factor 1 (PCIF1) is a methyltransferase that adds a methyl group to the N6-position of 2′O-methyladenosine (Am), generating N6, 2′O-dimethyladenosine (m6Am) when Am is the cap-proximal nucleotide. In addition, PCIF1 has ancillary methylation activities on internal adenosines (both A and Am), although with much lower catalytic efficiency relative to that of its preferred cap substrate. The PCIF1 preference for 2′O-methylated Am over unmodified A nucleosides is due mainly to increased binding affinity for Am. Importantly, it was recently reported that PCIF1 can methylate viral RNA. Although some viral RNA can be translated in the absence of a cap, it is unclear what roles PCIF1 modifications may play in the functionality of viral RNAs. Here we show, using in vitro assays of binding and methyltransfer, that PCIF1 binds an uncapped 5′-Am oligonucleotide with approximately the same affinity as that of a cap analog (KM = 0.4 versus 0.3 μM). In addition, PCIF1 methylates the uncapped 5′-Am with activity decreased by only fivefold to sixfold compared with its preferred capped substrate. We finally discuss the relationship between PCIF1-catalyzed RNA methylation, shown here to have broader substrate specificity than previously appreciated, and that of the RNA demethylase fat mass and obesity-associated protein (FTO), which demonstrates PCIF1-opposing activities on capped RNAs. 相似文献
13.
Recombinant frequency was compared with nucleotide distance in crosses involving markers in either the PRM or the cy region of phage λ. For each pair of markers, we performed reciprocal four-factor crosses of the following types: (I) A+m1 +m2-B- x A-m1 -m2+B+; and (II) A+m1 -m2+B- x A-m1 +m2-B+. In crosses of type I, the frequency of A+m1 +m2+B+ recombinants among total (selected) A+B+ progeny was directly proportional to nucleotide distance between m1 and m2 in the range from 3 to 160 nucleotides. When less than three nucleotides separated m1 and m2, the measured yields of m1+m2+ recombinants were significantly depressed.
We also found that the frequency of A+m1 +m2+B+ recombinants among total A+B+ progeny was significantly lower (about 10-fold on the average) in crosses of type II than in the corresponding crosses of type I. Since mismatch correction should yield A+m1 +m2+B+ recombinants with approximately equal frequencies in type I and II crosses, we suggest: (1) that most m1+m2+ recombinants produced in type I crosses must arise from the formation of heteroduplex structures with a discontinuity (in the source of genetic information) between sites m1 and m2, and (2) that mismatch correction is not a major pathway for production of recombinants for close markers in normal λ infection.
相似文献14.
Yuki Kato Tadao Shibamoto Shoichi Yamamoto Tadashi Watanabe Naoko Ishida Miwa Sugiura Fabrice Rappaport Alain Boussac 《BBA》2012,1817(11):1998-2004
Ca2+ and Cl? ions are essential elements for the oxygen evolution activity of photosystem II (PSII). It has been demonstrated that these ions can be exchanged with Sr2+ and Br?, respectively, and that these ion exchanges modify the kinetics of some electron transfer reactions at the Mn4Ca cluster level (Ishida et al., J. Biol. Chem. 283 (2008) 13330–13340). It has been proposed from thermoluminescence experiments that the kinetic effects arise, at least in part, from a decrease in the free energy level of the Mn4Ca cluster in the S3 state though some changes on the acceptor side were also observed. Therefore, in the present work, by using thin-layer cell spectroelectrochemistry, the effects of the Ca2+/Sr2+ and Cl?/Br? exchanges on the redox potential of the primary quinone electron acceptor QA, Em(QA/QA?), were investigated. Since the previous studies on the Ca2+/Sr2+ and Cl?/Br? exchanges were performed in PsbA3-containing PSII purified from the thermophilic cyanobacterium Thermosynechococcus elongatus, we first investigated the influences of the PsbA1/PsbA3 exchange on Em(QA/QA?). Here we show that i) the Em(QA/QA?) was up-shifted by ca. + 38 mV in PsbA3-PSII when compared to PsbA1-PSII and ii) the Ca2+/Sr2+ exchange up-shifted the Em(QA/QA?) by ca. + 27 mV, whereas the Cl?/Br? exchange hardly influenced Em(QA/QA?). On the basis of the results of Em(QA/QA?) together with previous thermoluminescence measurements, the ion-exchange effects on the energetics in PSII are discussed. 相似文献
15.
- The daily ration required to maintain a population growth rate, r m, of zero (threshold ration) increased with increasing Asplanchna body mass. This relationship is described by the equation T=0.342 W0.797 where T=threshold ration (μg day-1 dry mass) and W=Asplanchna body mass (μg adult-1 dry mass).
- The threshold ration of large campanulate morphs of A. silvestrii was 3.7 times greater than that of conspecific saccate morphs suggesting that campanulates may be restricted to food-rich habitats.
- The daily ration required to maintain r m that is half the maximal population growth rate increased with increasing Asplanchna body mass and is described by the equation H=1.107 W1.103 where H=ration level and W=Asplanchna body mass. This population growth characteristic may reflect adaptations of rotifers to resource level.
- The relationships between ration level, food concentration, and Asplanchna body mass do not support the predictions of the size-efficiency hypothesis but are consistent with observed patterns of species distribution in nature.
16.
Lingli Dong Naxin Huo Yi Wang Karin Deal Ming-Cheng Luo Daowen Wang Olin D. Anderson Yong Qiang Gu 《Molecular genetics and genomics : MGG》2012,287(11-12):855-866
The polyploid nature of hexaploid wheat (T. aestivum, AABBDD) often represents a great challenge in various aspects of research including genetic mapping, map-based cloning of important genes, and sequencing and accurately assembly of its genome. To explore the utility of ancestral diploid species of polyploid wheat, sequence variation of T. urartu (AuAu) was analyzed by comparing its 277-kb large genomic region carrying the important Glu-1 locus with the homologous regions from the A genomes of the diploid T. monococcum (AmAm), tetraploid T. turgidum (AABB), and hexaploid T. aestivum (AABBDD). Our results revealed that in addition to a high degree of the gene collinearity, nested retroelement structures were also considerably conserved among the Au genome and the A genomes in polyploid wheats, suggesting that the majority of the repetitive sequences in the A genomes of polyploid wheats originated from the diploid Au genome. The difference in the compared region between Au and A is mainly caused by four differential TE insertion and two deletion events between these genomes. The estimated divergence time of A genomes calculated on nucleotide substitution rate in both shared TEs and collinear genes further supports the closer evolutionary relationship of A to Au than to Am. The structure conservation in the repetitive regions promoted us to develop repeat junction markers based on the Au sequence for mapping the A genome in hexaploid wheat. Eighty percent of these repeat junction markers were successfully mapped to the corresponding region in hexaploid wheat, suggesting that T. urartu could serve as a useful resource for developing molecular markers for genetic and breeding studies in hexaploid wheat. 相似文献
17.
Djemel Hamdane Amandine Guelorget Vincent Guérineau Béatrice Golinelli-Pimpaneau 《Nucleic acids research》2014,42(18):11697-11706
In most organisms, the widely conserved 1-methyl-adenosine58 (m1A58) tRNA modification is catalyzed by an S-adenosyl-L-methionine (SAM)-dependent, site-specific enzyme TrmI. In archaea, TrmI also methylates the adjacent adenine 57, m1A57 being an obligatory intermediate of 1-methyl-inosine57 formation. To study this multi-site specificity, we used three oligoribonucleotide substrates of Pyrococcus abyssi TrmI (PabTrmI) containing a fluorescent 2-aminopurine (2-AP) at the two target positions and followed the RNA binding kinetics and methylation reactions by stopped-flow and mass spectrometry. PabTrmI did not modify 2-AP but methylated the adjacent target adenine. 2-AP seriously impaired the methylation of A57 but not A58, confirming that PabTrmI methylates efficiently the first adenine of the A57A58A59 sequence. PabTrmI binding provoked a rapid increase of fluorescence, attributed to base unstacking in the environment of 2-AP. Then, a slow decrease was observed only with 2-AP at position 57 and SAM, suggesting that m1A58 formation triggers RNA release. A model of the protein–tRNA complex shows both target adenines in proximity of SAM and emphasizes no major tRNA conformational change except base flipping during the reaction. The solvent accessibility of the SAM pocket is not affected by the tRNA, thereby enabling S-adenosyl-L-homocysteine to be replaced by SAM without prior release of monomethylated tRNA. 相似文献
18.
Molecular characterization and diversity of the Pina and Pinb genes in cultivated and wild diploid wheat 总被引:2,自引:0,他引:2
C. Guzmán L. Caballero M. A. Martín J. B. Alvarez 《Molecular breeding : new strategies in plant improvement》2012,30(1):69-78
Grain hardness is one of the most important characteristics of wheat quality. Soft endosperm is associated with the presence of two proteins in the wild form, puroindoline a and b. The puroindoline genes and their derived proteins are present in the putative wheat diploid ancestors which are thought to be the donors of the A, B and D genomes in common and durum wheat. In this study, we investigated the variability of grain hardness in einkorn, along with the nucleotide diversity of Pina and Pinb genes in a collection of einkorn wheat and T. urartu, in addition to studying the neutrality and linkage disequilibrium of these genes. Various alleles were detected for Pina and Pinb genes including three novel alleles for the Pinb locus: Pinb-A m 1i, Pinb-A m 1j and Pinb-A m 1k. Some differences were found in grain hardness between the different genotypes. The neutrality test showed a different pattern of variation between the two Pin genes. The genetic analysis of a diploid wheat collection has demonstrated that these species are a potential source of novel puroindoline variants. Our data suggest that, although further studies must be carried out, these variants could be used to expand the range of grain texture in durum and common wheat, which would permit the development of new materials adapted to novel uses in the baking and pasta industry. 相似文献
19.
A model separating leaf structural and physiological effects on carbon gain along light gradients for the shade-tolerant species Acer saccharum 总被引:27,自引:8,他引:19
A process-based leaf gas exchange model for C3 plants was developed which specifically describes the effects observed along light gradients of shifting nitrogen investment in carboxylation and bioenergetics and modified leaf thickness due to altered stacking of photosynthetic units. The model was parametrized for the late-successional, shade-tolerant deciduous species Acer saccharum Marsh. The specific activity of ribulose-1,5-bisphosphate carboxylase (Rubisco) and the maximum photosynthetic electron transport rate per unit cytochrome f (cyt f) were used as indices that vary proportionally with nitrogen investment in the capacities for carboxylation and electron transport. Rubisco and cyt f per unit leaf area are related in the model to leaf dry mass per area (MA), leaf nitrogen content per unit leaf dry mass (Nm), and partitioning coefficients for leaf nitrogen in Rubisco (PR) and in bioenergetics (PB). These partitioning coefficients are estimated from characteristic response curves of photosynthesis along with information on lear structure and composition. While PR and PB determine the light-saturated value of photosynthesis, the fraction of leaf nitrogen in thylakoid light-harvesting components (PL) and the ratio of leaf chlorophyll to leaf nitrogen invested in light harvesting (CB), which is dependent on thylakoid stoichiometry, determine the initial photosynthetic light utilization efficiency in the model. Carbon loss due to mitochondrial respiration, which also changes along light gradients, was considered to vary in proportion with carboxylation capacity. Key model parameters - Nm, PR, PB, PLCB and stomatal sensitivity with respect to changes in net photosynthesis (Gr) – were examined as a function of MA, which is linearly related to irradiance during growth of the leaves. The results of the analysis applied to A. saccharum indicate that PB and PR increase, and Gf, PL and CB decrease with increasing MA. As a result of these effects of irradiaiice on nitrogen partitioning, the slope of the light-saturated net photosynthesis rate per unit leaf dry mass (Ammax) versus Nm relationship increased with increasing growth irradiance in mid-season. Furthermore, the nitrogen partitioning coefficients as well as the slopes of Ammax versus Nm were independent of season, except during development of the leaf photosynthetic apparatus. Simulations revealed that the acclimation to high light increased Ammax by 40% with respect to the low light regime. However, light-saturated photosynthesis per leaf area (Aamax) varied 3-fold between these habitats, suggesting that the acclimation to high light was dominated by adjustments in leaf anatomy (Aamax=AmmaxMA) rather than in foliar biochemistry. This differed from adaptation to low light, where the alterations in foliar biochemistry were predicted to be at least as important as anatomical modifications. Due to the light-related accumulation of photosynthetic mass per unit area, Aamax depended on MA and leaf nitrogen per unit area (Na). However, Na conceals the variation in both MA and Nm (Na=NmMA), and prevents clear separation of anatomical adjustments in foliage structure and biochemical modifications in foliar composition. Given the large seasonal and site nutrient availability-related variation in Nm, and the influences of growth irradiance on nitrogen partitioning, the relationship between Aamax and Na is universal neither in time nor in space and in natural canopies at mid-season is mostly driven by variability in MA. Thus, we conclude that analyses of the effects of nitrogen investments on potential carbon acquisition should use mass-based rather than area-based expressions. 相似文献
20.
The effects of pressure on the kinetics of redox reactions in and around the chloroplast cytochrome bf complex were studied using a reconstituted system consisting of Photosystem I (PS I) particles, cytochrome bf complex and plastocyanin (PC), all derived from pea chloroplasts. There were no significant permanent effects of pressure in the range 0.1–191 MPa on the reaction kinetics, or on the shape of the absorption spectra of components studied. Discernable effects on rate-coefficients of increasing pressure were observed on the reduction of P700+ by PCI, on the reduction of PCII by ascorbate, and on the oxidation of decyl plastoquinol by the bf complex. The volumes of activation ΔV# were determined from the dependence of the rate-coefficient on pressure using: $$(\partial lnk/\partial P)_T = - \Delta V^\# /RT.$$ The volume of activation is the difference in partial molar volume between the activated state and the reactants for the redox reaction. Such data was sought to help define in detail those redox reactions and the corresponding activated states. For the reduction of P700+ by PCI and the oxidation of decyl plastoquinol by the bf complex, the rate coefficient decreased with increase in pressure, whilst for the reduction of PCII by ascorbate it increased. The corresponding volumes of activation were 9.6±0.6×10-6 m3 mol-1, 18±2×10-6 m3 mol-1 and -14±1×10-6 m3 mol-1, respectively. Much of the pressure-dependence of PCII reduction by ascorbate was ascribed to an increase in ascorbate ionisation with increase in pressure. There was little effect of pressure on the kinetics of oxidation of ferrocytochrome f by PCII, or on the equilibrium constant of the redox pair ferrocytochrome f/ferricytochrome f: PCII/PCI. Possible physical bases for these activation volumes are discussed, and they are compared with literature values. 相似文献