Interspecies Acetate Transfer Influences the Extent of Anaerobic Benzoate Degradation by Syntrophic Consortia

Benzoate degradation by an anaerobic, syntrophic bacterium, strain SB, in coculture with Desulfovibrio sp. strain G-11 reached a threshold value which depended on the amount of acetate added and ranged from about 2.5 to 29.9 (mu)M. Increasing acetate concentrations also uncompetitively inhibited benzoate degradation. The apparent V(infmax) and apparent K(infm) for benzoate degradation decreased with increasing acetate concentration, but the benzoate degradation capacities (V(infmax)/K(infm)) of cell suspensions remained comparable. The addition of an acetate-using bacterium to cocultures after the threshold was reached resulted in the degradation of benzoate to below the detection limit. Mathematical simulations showed that the benzoate threshold was not predicted by the inhibitory effect of acetate on benzoate degradation kinetics. With nitrate instead of sulfate as the terminal electron acceptor, no benzoate threshold was observed in the presence of 20 mM acetate even though the kinetics of benzoate degradation were slower with nitrate rather than sulfate as the electron acceptor. When strain SB was grown with Desulfovibrio sp. strain DG2 that had a fourfold-lower V(infmax) for hydrogen use than strain G-11, the V(infmax) for benzoate degradation was 37-fold lower than that of strain SB-G-11 cocultures. The Gibb's free energy for benzoate degradation was less negative in cell suspensions with a threshold than in suspensions without a threshold. These studies showed that the threshold was not a function of the inhibition of benzoate degradation by acetate or the toxicity of the undissociated form of acetate. Rather, a critical or minimal Gibb's free energy may exist where thermodynamic constraints preclude further benzoate degradation.     

Rates of Water Loss and Uptake in Recalcitrant Fruits of Quercus Species Are Determined by Pericarp Anatomy

Desiccation-sensitive recalcitrant seeds and fruits are killed by the loss of even moderate quantities of water. Consequently, minimizing the rate of water loss may be an important ecological factor and evolutionary driver by reducing the risk of mortality during post-dispersal dry-spells. For recalcitrant fruits of a range of Quercus species, prolonged drying times have been observed previously. However, the underlying mechanism(s) for this variation is unknown. Using nine Quercus species we investigated the major route(s) of water flow into and out of the fruits and analysed the relative importance of the different pericarp components and their anatomy on water uptake/loss. During imbibition (rehydration), the surface area of the cupule scar and the frequency and area of the vascular bundles contained therein were significantly correlated with the rates of water uptake across the scar. The vascular bundles serving the apex of the fruit were a minor contributor to overall water. Further, the rate of water uptake across the remainder of the pericarp surface was significantly correlated with the thickness of the vascularised inner layer in the pericarp. Fruits of Q. franchetii and Q. schottkyana dried most slowly and had a comparatively small scar surface area with few vascular bundles per unit area. These species inhabit drier regions than the other species studied, suggesting these anatomical features may have ecological value by reducing the risk of desiccation stress. However, this remains to be tested in the field.     

三峡库区岸边共存松栎树种水分利用策略比较

对三峡库区木鱼岛上马尾松(Pinus massoniana)、槲栎(Quercus aliena)和栓皮栎(Q. variabilis)组成的针阔混交林成林和幼林的光合速率(P_n)、气孔导度(G_s)、清晨和中午水势(ψ_pd和ψ_md)以及叶片稳定碳同位素(δ¹³C)进行了测定。实验结果表明:针叶树马尾松P_n、G_s均低于阔叶树槲栎和栓皮栎(差异达到极显著水平,p<0.001),但马尾松内在水分利用效率(WUE_i, P_n/G_s)却高于槲栎(p=0.003)和栓皮栎(p=0.025)。反映了裸子植物和被子植物木质部不同的水力特性。针阔叶树幼树的P_n和G_s高于成年树,但WUE_i和δ¹³C却低于成年树。表明水分利用效率与水分在树体内传输的距离有关。幼树属于挥霍型水分利用策略,成年树属保守型水分利用策略。三峡大坝的建设所造成的生态环境的改变可能会对三峡库区针阔混交林的演替产生一定的影响,但这需要长期的研究。     

壳斗科三种植物种子大小对昆虫寄生及种子存活率的影响

种子内的寄生昆虫可以严重影响种子的发育、损害种子活力。种子足余策略理论认为大种子有利于抵御和适应昆虫寄生取食,但动物最优觅食理论推测,大种子更易遭受昆虫寄生。为对这两种对立观点进行验证,本实验以青冈、苦槠和麻栎各2个种群的种子为材料,对昆虫寄生与完好种子间的体积和萌发率进行比较,并对寄生种子萌发率与种子体积的关系进行了分析。结果显示:(1)在6个种群的种子中,只有松阳麻栎和青冈种群的寄生种子体积大于完好种子,其余4个种群的寄生种子体积小于完好种子,但这种差异不显著;(2)所有寄生种子的整体萌发率(18%)显著低于完好种子(45.66%)(P<0.001),在不同种群内,寄生种子的萌发率也分别显著低于完好种子。(3)比较同种植物体积差异显著的寄生种子的萌发率发现,大种子总比小种子具有更高的萌发率,但差异不显著;在不同植物的寄生种子间比较时,体积最大的麻栎种子萌发率显著高于体积较小的青冈和苦槠种子。研究结果表明,象虫在种子上产卵时对大种子没有选择偏好,在昆虫寄生取食严重损害种子活力的压力下,大种子比小种子具有更强的耐受力。     

Use of a quantitative oxidase test for characterizing oxidative metabolism in bacteria.

It was possible to quantitate the terminal oxidase(s) reaction using bacterial resting-cell suspensions and demonstrate the usefulness of this reaction for taxonomic purposes. Resting-cell suspensions of physiologically diverse bacteria were examined for their capabilities of oxidizing N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) using a manometric assay. For organisms having this capability, it was possible to calculate the conventional TMPD oxidase Q(O2) value (microliters of O2 consumed per hour per milligram [dry weight]). All cultures were grown heterotrophically at 30 C, under identical nutritional conditions, and were harvested at the late-logarithmic growth phase. The TMPD oxidase Q(O2) values showed perfect correlation with the Kovacs oxidase test and, in addition, it was possible to define quantitatively that point which separated oxidase-positive from oxidase-negative bacteria. Oxidase-negative bacteria exhibited a TMPD oxidase Q(O2) value (after correcting for the endogenous by substraction) of less than or equal 33 and had an uncorrected TMPD/endogenous ratio of less than or equal 5. The TMPD oxidase Q(O2) values were also correlated with the data obtained for the Hugh-Leifson Oxferm test. In general, bacteria that exhibited a respiratory mechanism had high TMPD oxidase values, whereas fermentative organsims had low TMPD oxidase activity. All exceptions to this are noted. This quantitative study also demonstrated that organisms that (i) lack a type c cytochrome, or (ii) lack a cytochrome-containing electron transport system, like the lactic acid bacteria, exhibited low or negligible TMPD oxidase Q(O2) values. From the 79 bacterial species (36 genera) examined, it appears that this quantitative oxidase test has taxonomic value that can differentiate the oxidative relationships between bacteria at the subspecies, species, and genera levels.     

Use of a quantitative oxidase test for characterizing oxidative metabolism in bacteria.

It was possible to quantitate the terminal oxidase(s) reaction using bacterial resting-cell suspensions and demonstrate the usefulness of this reaction for taxonomic purposes. Resting-cell suspensions of physiologically diverse bacteria were examined for their capabilities of oxidizing N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) using a manometric assay. For organisms having this capability, it was possible to calculate the conventional TMPD oxidase Q(O2) value (microliters of O2 consumed per hour per milligram [dry weight]). All cultures were grown heterotrophically at 30 C, under identical nutritional conditions, and were harvested at the late-logarithmic growth phase. The TMPD oxidase Q(O2) values showed perfect correlation with the Kovacs oxidase test and, in addition, it was possible to define quantitatively that point which separated oxidase-positive from oxidase-negative bacteria. Oxidase-negative bacteria exhibited a TMPD oxidase Q(O2) value (after correcting for the endogenous by substraction) of less than or equal 33 and had an uncorrected TMPD/endogenous ratio of less than or equal 5. The TMPD oxidase Q(O2) values were also correlated with the data obtained for the Hugh-Leifson Oxferm test. In general, bacteria that exhibited a respiratory mechanism had high TMPD oxidase values, whereas fermentative organsims had low TMPD oxidase activity. All exceptions to this are noted. This quantitative study also demonstrated that organisms that (i) lack a type c cytochrome, or (ii) lack a cytochrome-containing electron transport system, like the lactic acid bacteria, exhibited low or negligible TMPD oxidase Q(O2) values. From the 79 bacterial species (36 genera) examined, it appears that this quantitative oxidase test has taxonomic value that can differentiate the oxidative relationships between bacteria at the subspecies, species, and genera levels.     

Evidence for Intracellular and Extracellular Dimethylsulfoniopropionate (DMSP) Lyases and DMSP Uptake Sites in Two Species of Marine Bacteria

The kinetics of dimethylsulfoniopropionate (DMSP) uptake and dimethylsulfide (DMS) production from DMSP in two bacterial species, Alcaligenes sp. strain M3A, an isolate from estuarine surface sediments, and Pseudomonas doudoroffii, from seawater, were investigated. In Alcaligenes cells induced for DMSP lyase (DL) activity, DMS production occurred without DMSP uptake. In DL-induced suspensions of P. doudoroffii, uptake of DMSP preceded the production of DMS, indicating an intracellular location of DL; intracellular DMSP levels reached ca. 7 mM. DMSP uptake rates in noninduced cells showed saturation at three concentrations (K(inft) [transport] values, 3.4, 127, and 500 (mu)M). In DL-induced cells of P. doudoroffii, DMSP uptake rates increased ca. threefold (V(infmax), 0.022 versus 0.065 (mu)mol of DMSP taken up min(sup-1) mg of cell protein(sup-1)), suggesting that the uptake binding proteins were inducible. DMSP uptake and DL activity in P. doudoroffii were both inhibited by CN(sup-), 2,4-dinitrophenol, and membrane-impermeable thiol-binding reagents, further indicating active uptake of DMSP by cell surface components. The respiratory inhibitors had limited or no effect on DL activity by the Alcaligenes sp. Of the structural analogs of DMSP tested for their effect on DMSP metabolism, glycine betaine (GBT), but not methyl-3-mercaptopropionic acid (MMPA), inhibited DMSP uptake by P. doudoroffii, suggesting that GBT shares a binding protein with DMSP and that MMPA is taken up at a separate site. Two models of DMSP uptake, induction, and DL location found in marine bacteria are presented.     

Uptake,demand and internal cycling of nitrogen in saplings of Mediterranean<Emphasis Type="Italic"> Quercus</Emphasis> species

Nitrogen uptake, nitrogen demand and internal nitrogen cycling were studied to address the question of the importance of nutrient storage in Quercus species with contrasting leaf longevities. We carried out this study at the whole-plant level with young trees (2-4 years old) of three Mediterranean Quercus species: the evergreen Q. ilex, the marcescent/evergreen Q. faginea, and the deciduous Q. pyrenaica. Seasonal dynamics of nitrogen in all compartments of the plant were followed for 3 years. Nitrogen losses were measured through litter production, herbivory and fine root shedding. Nitrogen uptake was estimated using increments of nitrogen plant content plus accumulative nitrogen losses. Nitrogen uptake was limited to a few months during late winter and spring. Before budbreak, acquired nitrogen was stored in old-leaf cohorts of evergreen and woody compartments. After budbreak, Quercus species relied first on soil uptake and second on nitrogen retranslocation to supply new growth requirements. However, in most cases we found a high asynchrony between nitrogen demand by growing tissues and soil supply, which determined a strong nitrogen retranslocation up to 88.4% of the nitrogen demand throughout leaf expansion. Except for the first year after planting, the above- and underground woody fractions provided more nitrogen to the new tissues than the old leaf cohorts. Differences in the benefit of nitrogen withdrawn from senescent and old leaves were not found between species. We conclude that sink/source interaction strength was determined by differences between nitrogen demand and uptake, regulating internal nutrient cycling at the whole plant level.     

Distribution of genomic regions differentiating oak species assessed by QTL detection

Pedunculate oak and sessile oak are two sympatric interfertile species that exhibit leaf morphological differences. We aimed to detect quantitative trait loci (QTLs) of these traits in order to locate genomic regions involved in species differentiation. A total of 15 leaf morphological traits were assessed in a mixed forest stand composed of Quercus petraea and Q. robur and in a full-sib pedigree of Q. robur. The progeny of the full-sib family were vegetatively propagated in two successive experiments comprising 174 and 216 sibs, and assessments were made on two leaves collected on each of the 1080 and 1530 cuttings corresponding to the two experiments. Traits that exhibited strong species differences in the mixed stand tended also to have higher repeatability values in the mapping population, thus indicating higher genetic control. A genetic map was constructed for QTL detection. Composite interval mapping with the one QTL model was used for QTL detection. From one to three QTLs were detected for 13 traits. In-depth analysis of the QTLs, controlling the five morphological traits that exhibited the highest interspecific differences in the mixed stand, indicated that they were distributed on six linkage groups, with two clusters comprising QTLs of at least two discriminant traits. These results were reinforced when error 1 for QTL detection was set at 5% at the chromosome level, as up to nine clusters could be identified. In conclusion, traits involved in interspecific differentiation of oaks are under polygenic control and widespread in clusters across the genome.     

Uptake of Benzoic Acid and Chloro-Substituted Benzoic Acids by Alcaligenes denitrificans BRI 3010 and BRI 6011

The mechanism of uptake of benzoic and 2,4-dichlorobenzoic acid (2,4-DCBA) by Alcaligenes denitrificans BRI 3010 and BRI 6011 and Pseudomonas sp. strain B13, three organisms capable of degrading various isomers of chlorinated benzoic acids, was investigated. In all three organisms, uptake of benzoic acid was inducible. For benzoic acid uptake into BRI 3010, monophasic saturation kinetics with apparent K(infm) and V(infmax) values of 1.4 (mu)M and 3.2 nmol/min/mg of cell dry weight, respectively, were obtained. For BRI 6011, biphasic saturation kinetics were observed, suggesting the presence of two uptake systems for benzoic acid with distinct K(infm) (0.72 and 5.3 (mu)M) and V(infmax) (3.3 and 4.6 nmol/min/mg of cell dry weight) values. BRI 3010 and BRI 6011 accumulated benzoic acid against a concentration gradient by a factor of 8 and 10, respectively. A wide range of structural analogs, at 50-fold excess concentrations, inhibited benzoic acid uptake by BRI 3010 and BRI 6011, whereas with B13, only 3-chlorobenzoic acid was an effective inhibitor. For BRI 3010 and BRI 6011, the inhibition by the structural analogs was not of a competitive nature. Uptake of benzoic acid by BRI 3010 and BRI 6011 was inhibited by KCN, by the protonophore 3,5,3(prm1), 4(prm1)-tetrachlorosalicylanilide (TCS), and, for BRI 6011, by anaerobiosis unless nitrate was present, thus indicating that energy was required for the uptake process. Uptake of 2,4-DCBA by BRI 6011 was constitutive and saturation uptake kinetics were not observed. Uptake of 2,4-DCBA by BRI 6011 was inhibited by KCN, TCS, and anaerobiosis even if nitrate was present, but the compound was not accumulated intracellularly against a concentration gradient. Uptake of 2,4-DCBA by BRI 6011 appears to occur by passive diffusion into the cell down its concentration gradient, which is maintained by the intracellular metabolism of the compound. This process could play an important role in the degradation of xenobiotic compounds by microorganisms.     

Biosynthetic characterization and biochemical features of the third natural nisin variant,nisin Q,produced by Lactococcus lactis 61‐14

Aims: To characterize the genetic and biochemical features of nisin Q. Methods and Results: The nisin Q gene cluster was sequenced, and 11 putative orfs having 82% homology with the nisin A biosynthesis gene cluster were identified. Nisin Q production was confirmed from the nisQ‐introduced nisin Z producer. In the reporter assay, nisin Q exhibited an induction level that was threefold lower than that of nisin A. Nisin Q demonstrated an antimicrobial spectrum similar to those of the other nisins. Under oxidizing conditions, nisin Q retained a higher level of activity than nisin A. This higher oxidative tolerance could be attributed to the presence of only one methionine residue in nisin Q, in contrast to other nisins that contain two. Conclusions: The 11 orfs of the nisin producers were identical with regard to their functions. The antimicrobial spectra of the three natural nisins were similar. Nisin Q demonstrated higher oxidative tolerance than nisin A. Significance and Impact of the Study:  Genetic and biochemical features of nisin Q are similar to those of other variants. Moreover, owing to its higher oxidative tolerance, nisin Q is a potential alternative for nisin A.     

Potential impact of global warming on deciduous oak dieback caused by ambrosia fungus Raffaelea sp. carried by ambrosia beetle Platypus quercivorus (Coleoptera: Platypodidae) in Japan

Deciduous oak dieback in Japan has been known since the 1930s, but in the last ten years epidemics have intensified and spread to the island's western coastal areas. The symbiotic ambrosia fungus Raffaelea sp. is the causal agent of oak dieback, and is vectored by Platypus quercivorus (Murayama). This is the first example of an ambrosia beetle fungus that kills vigorous trees. Mortality of Quercus crispula was approximately 40% but much lower for associated species of Fagaceae, even though each species had a similar number of beetle attacks. It is likely that other oaks resistant to the fungus evolved under a stable relationship between the tree, fungus and beetle during a long evolutionary process. Quercus crispula was probably not part of this coevolution. This hypothesis was supported by the fact that P. quercivorus showed the least preference for Q. crispula yet exhibited highest reproductive success in this species. Therefore, P. quercivorus could spread more rapidly in stands with a high composition of Q. crispula. The present oak dieback epidemic in Japan probably resulted from the warmer climate that occurred from the late 1980s which made possible the fateful encounter of P. quercivorus with Q. cripsula by allowing the beetle to extend its distribution to more northerly latitudes and higher altitudes. Future global warming will possibly accelerate the overlapping of the distributions of P. quercivorus and Q. crispula with the result that oak dieback in Q. crispula will become more prevalent in Japan.     

Dehydration tolerance of leaf tissues of six woody angiosperm species

Electrolyte leakage from leaf discs (measured as an index of dehydration tolerance) increased as water potentials of excised leaves declined for field-grown saplings of six woody species. Until late in the growing season (mid-August), leaves of Cornus florida L. exhibited greater leakage than those of other species; however, in August and September leakage in this species was much reduced, indicating apparent hardening in response to mid-season drought. Leaves of Quercus alba L., Q. rubra L. and Q. velutina Lam. generally exhibited less electrolyte leakage than did those of Acer saccharum Marsh, and Juglans nigra L. over the season. Moreover, leaves of Quercus species showed a reduction in electrolyte leakage late in the season similar to (but less accentuated than) that of C. florida . Saplings of A. saccharum and J. nigra showed little and no drought-hardening response, respectively. The responses shown by the studied species suggest that dehydration tolerance plays a role in plant distribution and that environmentally induced shifts in this tolerance are a significant phenomenon in natural plant communities.     

Hydraulic disruption and passive migration by a bacterial pathogen in oak tree xylem

Xylella fastidiosa (Xf) is a xylem-limited bacterial pathogen that causes leaf scorch symptoms in numerous plant species in urban, agricultural, and natural ecosystems worldwide. The exact mechanism of hydraulic disruption and systemic colonization of xylem by Xf remains elusive across all host plants. To understand both processes better, the functional and structural characteristics of xylem in different organs of both healthy and Xf-infected trees of several Quercus species were studied. Hydraulic conductivity (K(s)) in Xf-infected petioles of Q. palustris and Q. rubra decreased significantly compared with healthy trees as the season progressed and plummeted to zero with the onset of scorch symptoms. Prior to the onset of symptoms, embolism was as much as 3.7 times higher in Xf-infected petioles compared with healthy controls and preceded significant reductions in K(s). Embolism likely resulted from pit membrane degradation during colonization of new petiole xylem and triggered the process that eventually led to vessel occlusion. Pit membrane porosity was studied using the following four methods to determine if a pathway exists in the xylem network of woody stems that allows for passive Xf migration: (i) calculations based on vulnerability to cavitation data, (ii) scanning electron micrographs, (iii) microsphere injections, and (iv) air seeding thresholds on individual vessels. All four methods consistently demonstrated that large pit membrane pores (i.e. greater than the diameter of individual Xf) occur frequently throughout the secondary stem xylem in several Quercus species. These large pores probably facilitate systemic colonization of the secondary xylem network and contribute to the high susceptibility to bacterial leaf scorch exhibited among these species.     

Relatively large nitrate efflux can account for the high specific respiratory costs for nitrate transport in slow-growing grass species

In this paper we address the question why slow-growing grass species appear to take up nitrate with greater respiratory costs than do fast-growing grasses when all plants are grown with free access to nutrients. Specific costs for nitrate transport, expressed as moles of ATP per net mole of nitrate taken up, were 1.5 to 4 times higher in slow-growing grasses than in fast-growing ones (Scheurwater et al., 1998, Plant, Cell & Environ. 21, 995–1005). The net rate of nitrate uptake is determined by two opposing nitrate fluxes across the plasma membrane: influx and efflux. To test whether differences in specific costs for nitrate transport are due to differences in the ratio of nitrate influx to net rate of nitrate uptake, nitrate influx and the net rate of nitrate uptake were measured in the roots of two fast-growing ( Dactylis glomerata L. and Holcus lanatus L.) and two slow-growing (Deschampsia flexuosa L. and Festuca ovina L.) grass species at four points during the diurnal cycle, using ¹⁵NO₃ ^-. Efflux was calculated by subtraction of net uptake from influx; it was assumed that efflux of nitrogen represents the flux of nitrate. Transfer of the plants to the solution containing the labelled nitrate did not significantly affect nitrate uptake in the present grass species. The net rate of nitrate uptake was highest during the middle of the light period in all species. Diurnal variation in the net rate of nitrate uptake was mostly due to variation in nitrate influx. Variation in nitrate efflux did not occur in all species, but efflux per net mole of nitrate taken up was higher during darkness than in the light in the slow-growing grasses. The two fast-growing species, however, did not show diurnal variation in the ratio of efflux to net nitrate uptake. Integrated over 24 hours, the slow-growing grasses clearly exhibited higher ratios of influx to net uptake than the fast-growing grass species. Our results indicate that the higher ratio of nitrate influx to net nitrate uptake can account for higher specific costs for nitrate transport in slow-growing grass species compared with those in their fast-growing counterparts, possibly in combination with greater activity of the non-phosphorylating alternative respiratory path. Therefore, under our experimental conditions with plants grown at a non-limiting nitrate supply, nitrate uptake is less efficient (from the point of ATP consumption) in slow-growing grasses than in fast-growing grass species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Convenient Model To Describe the Combined Effects of Temperature and pH on Microbial Growth

A new model in which the maximum microbial specific growth rate ((mu)(infmax)) is described as a function of pH and temperature is presented. The seven parameters of this model are the three cardinal pH parameters (the pH below which no growth occurs, the pH above which no growth occurs, and the pH at which the (mu)(infmax) is optimal), the three cardinal temperature parameters (the temperature below which no growth occurs, the temperature above which no growth occurs, and the temperature at which the (mu)(infmax) is optimal), and the specific growth rate at the optimum temperature and optimum pH. The model is a combination of the cardinal temperature model with inflection and the cardinal pH model (CPM). The CPM was compared with the models of Wijtzes et al. and Zwietering et al. by using previously published data sets. The models were compared on the basis of the usual criteria (simplicity, biological significance and minimum number of parameters, applicability, quality of fit, minimum structural correlations, and ease of initial parameter estimation), and our results justified the choice of the CPM. Our combined model was constructed by using the hypothesis that the temperature and pH effects on the (mu)(infmax) are independent. An analysis of this new model with an Escherichia coli O157:H7 data set showed that there was a good correspondence between observed and calculated (mu)(infmax) values. The potential and convenience of the model are discussed.     

Purification and Characterization of Two Dihydroxyacetone Kinases from Schizosaccharomyces pombe IFO 0354

Two dihydroxyacetone kinases (DHAKs), DHAK I and DHAK II, were purified to homogeneity from Schizosaccharomyces pombe IFO 0354. They were immunologically different from each other. Although both of the enzymes had some affinity for glycerol and dl-glyceraldehyde in addition to dihydroxyacetone and glyceraldehyde, V(infmax) values for dihydroxyacetone were much higher than those for glycerol and dl-glyceraldehyde. On the basis of the K(infm) values of both enzymes for dihydroxyacetone, DHAK II plays a more important role than DHAK I in dissimilation of glycerol via dihydroxyacetone.     

Differences between VO2 maxima of twitch and tetanic contractions are related to blood flow

The purpose of this investigation was to compare oxygen uptake (VO2) and fatigue characteristics of isotonic tetanic contractions with those observed during isotonic twitches in dog gastrocnemius-plantaris muscle. Tetanic contractions (1/s, 200-ms trains of 50 impulses/s) elicited a peak VO2 of 9.01 +/- 0.42 mumol.g-1.min-1, which declined 29% in 30 min. The peak was significantly lower during 4/s twitches (6.23 +/- 0.36 mumol.g-1.min-1), but the rate of decline was similar. Peak blood flow (Q) was 37% higher and decreased more slowly during tetanic than twitch contractions. VO2/Q and VO2/venous PO2 were similar in both groups at peak VO2 and later declined or remained constant over time. Power was significantly greater with tetanic contractions with the relative decline between 3 and 30 min similar in both groups (32 and 37%). In conclusion, tetanic contractions result in significantly higher VO2 and power than do twitch contractions. This was derived primarily from increased Q because the arteriovenous O2 difference was similar. A significant determinant of the difference in Q between twitch and tetanic contractions is mechanical hindrance of Q. There is relatively more time for unhindered flow in the tetanic contractions. In electrically stimulated muscles, maximal VO2 is related to Q and reflects mainly Q through the muscle rather than the VO2 capacity of the muscle.     

Genome scanning for interspecific differentiation between two closely related oak species [Quercus robur L. and Q. petraea (Matt.) Liebl.

Interspecific differentiation values (G(ST)) between two closely related oak species (Quercus petraea and Q. robur) were compiled across different studies with the aim to explore the distribution of differentiation at the genome level. The study was based on a total set of 389 markers (isozymes, AFLPs, SCARs, microsatellites, and SNPs) for which allelic frequencies were estimated in pairs of populations sampled throughout the sympatric distribution of the two species. The overall distribution of G(ST) values followed an L-shaped curve with most markers exhibiting low species differentiation (G(ST) < 0.01) and only a few loci reaching >10% levels. Twelve percent of the loci exhibited significant G(ST) deviations to neutral expectations, suggesting that selection contributed to species divergence. Coding regions expressed higher differentiation than noncoding regions. Among the 389 markers, 158 could be mapped on the 12 linkage groups of the existing Q. robur genetic map. Outlier loci with large G(ST) values were distributed over 9 linkage groups. One cluster of three outlier loci was found within 0.51 cM; but significant autocorrelation of G(ST) was observed at distances <2 cM. The size and distribution of genomic regions involved in species divergence are discussed in reference to hitchhiking effects and disruptive selection.     

Comparison of phenolic compounds and the effects of invasive and native species in East Asia: support for the novel weapons hypothesis

One prediction of the novel weapons hypothesis (NWH) for the dominance of exotic invasive plant species is that the allelopathic effects of successful invaders will, in general, be more biochemically inhibitory to native species and microbes in invaded regions than the native plants themselves. However, no study has compared biochemical concentrations, compositions, or effects of large numbers of native species to those of large numbers of invasive species. In this context we tested the allelopathic and antimicrobial potentials of nine native plant species and nine invasive species in East Asia by comparing their broad phenolic contents and the effects of extracts made from each of the species on target plants and soil fungi. Three of the invasive species, including Eupatorium rugosum, had higher concentrations of total phenolic compounds than any of the native species, and the mean concentration of total phenolics for invasive species was 2.6 times greater than the mean for native species. Only scopoletin was novel to the invasive species, being found in all of nine invasive species, but not in the native species. More importantly, the effects of the total suites of phenolic compounds produced by invasive species differed from the effects of phenolics produced by natives. Extracts of invasive species reduced radicle growth of the three test plant species by 60–80%, but extracts of native species reduced radicle growth by only 30–50%. Extracts of invasive species reduced shoot growth of the three test species by 20–40%, but the overall effect of native species’ extract was to stimulate shoot growth. The antimicrobial activity of invasive species was also significantly higher than that of native species. It should be noted that phenolics are just one component of a plant’s potential allelopathic arsenal and non-phenolic compounds are likely to play a role in the total extract effect. For example, extracts of P. americana contained the lowest levels of phenolic compounds, but exhibited the strongest inhibition effect. We could not determine whether the greater inhibitory effects of the extracts from invasive species were due to novel combinations of chemicals or higher concentrations of chemicals, but our results are consistent with the predictions of the NWH.