The Anisotropy of the Mesophyll and CO2 Capture Sites in Vicia faba L. Leaves at Low Light Intensities

Experiments are reported on the spatial distributions of isotopiccarbon within the mesophyll of detached leaves of the C₃ plantVicia faba L. fed ¹⁴CO₂ at different light intensities. Eachleaf was isolated in a cuvette and ten artificial stomata providedspatial continuity between the ambient atmosphere (0.03–0.05%v/v CO₂) and the mesophyll from the abaxial leaf side. Paradermalleaf layers exhibited spatial profiles of radioactivity whichvaried with the intensity of incident light in 2 min exposures.At low light, when biochemical kinetics should limit CO₂ uptake,sections through palisade cells contained most radioactivity.As the light intensity was increased to approximately 20% offull sunlight, peak radioactivity was observed in the spongycells near the geometric mid-plane of the mesophyll. The resultsindicate that diffusion of carbon dioxide within the mesophyllregulated the relative photosynthetic activity of the palisadeand spongy cells at incident photosynthetically active lightintensities as little as 110 µE m^–2 s^–1 whenCO₂ entered only through the lower leaf surface. Key words: CO₂ capture sites, Vicia faba L., Artificial stomata     

Bat Systematics in the Light of Unconstrained Analyses of a Comprehensive Molecular Supermatrix

Bats (Chiroptera) represent the largest diversification of extant mammals after rodents. Here we report the results of a large-scale phylogeny of bats based on unconstrained searches for a data matrix of 804 non-chimeric, taxonomically updated bat terminals (796 species represented by a single terminal plus three species represented by ≥2 genetically distinct subspecies), able to preliminary test the systematics of most groups simultaneously. We used nine nuclear and mitochondrial DNA sequence markers fragmentary represented for ingroups (c. 90% and 64% of extant diversity at genus and species level, respectively) and 20 diverse placental outgroups. Maximum Likelihood and Parsimony analyses applied to the concatenated dataset yielded a highly resolved, variously supported phylogeny that recovered the majority of currently recognized clades at all levels of the chiropteran tree. Calibration points based on 44 key fossils allowed the Bayesian dating of bat origins at c. 4 my after the K-Pg boundary, and the determination of stem and crown ages of intraordinal clades. As expected, bats appeared nested in Laurasiatheria and split into Yinpterochiroptera and Yangochiroptera. More remarkable, all polytypic, currently recognized families were monophyletic, including Miniopteridae, Cistugidae, and Rhinonycteridae, as well as most polytypic genera with few expected exceptions (e.g., Hipposideros). The controversial Myzopodidae appeared in a novel position as sister of Emballonuroidea―a result with interesting biogeographic implications. Most recently recognized subfamilies, genera, and species groups were supported or only minor adjustments to the current taxonomy would be required, except Molossidae, which should be revised thoroughly. In light of our analysis, current bat systematics is strongly supported at all levels; the emergent perception of a strong biogeographic imprint on many recovered bat clades is emphasized.     

The Influence of Light on Geotropism in Cress Roots

Light affects the growth and orientation of roots of cress seedlings(Lepidium sativum L. cv. Curled). The effects are manifest eitheras increased rates of geotropic curvature or, if the roots arehorizontal, as distorted and crinkled forms of growth. Blue,red, and far-red irradiation can bring about these effects,but with differences of detail: at equal fluence rates duringthe period of geostimulus, blue is more effective than red atincreasing the rate of geocurvature; however, with irradiationprior to a geostimulus, only the stimulatory effects of redirradiation persist for 2–4 h of darkness. Short periods(5 min) of radiation, if given at the time of geostimulus, enhancegeocurvature, again with blue most, and far-red least, effective,but there are no clear indications of red/far-red reversibility.The possibility of there being more than one photosystem responsiblefor the effects of white light on the geotropic responsivenessof roots is discussed.     

光照强度对小麦苗期草酸氧化酶活性的影响

以小麦品种‘烟优361’(Triticum aestivum L.cv.Yanyou 361)萌发4 d幼苗为试验材料,分析了草酸氧化酶(OxO)在幼苗中的定位和表达,以及光照强度处理对小麦幼苗OxO活性的影响。实验结果显示,萌发后小麦幼苗的OxO分布在子叶与根的连接处和成熟的根中,其活性随光照强度的增加而下降;200μmol.m-2.s-1的强光显著抑制了OxO活性,该处理培养4 d幼苗的OxO活性仅为40μmol.m-2.s-1光照培养条件下的18.7%;强光还缩短OxO在苗期的表达时间,抑制了OxO的mRNA表达量。同时,光照强度还能影响小麦幼苗中H2O2的含量,200μmol.m-2.s-1处理幼苗的H2O2的含量显著下降,其培养4 d的幼苗H2O2含量仅为40μmol.m-2.s-1光照强度培养条件下的18.0%。研究发现,光照强度可通过调节OxO的活性和表达量来控制H2O2的产量,从而影响幼苗的生长发育。     

A Behavioral Assay to Measure Responsiveness of Zebrafish to Changes in Light Intensities

The optokinetic reflex (OKR) is a basic visual reflex exhibited by most vertebrates and plays an important role in stabilizing the eye relative to the visual scene. However, the OKR requires that an animal detect moving stripes and it is possible that fish that fail to exhibit an OKR may not be completely blind. One zebrafish mutant, the no optokinetic response c (nrc) has no OKR under any light conditions tested and was reported to be completely blind. Previously, we have shown that OFF-ganglion cell activity can be recorded in these mutants. To determine whether mutant fish with no OKR such as the nrc mutant can detect simple light increments and decrements we developed the visual motor behavioral assay (VMR). In this assay, single zebrafish larvae are placed in each well of a 96-well plate allowing the simultaneous monitoring of larvae using an automated video-tracking system. The locomotor responses of each larva to 30 minutes light ON and 30 minutes light OFF were recorded and quantified. WT fish have a brief spike of motor activity upon lights ON, known as the startle response, followed by return to lower-than baseline activity, called a freeze. WT fish also sharply increase their locomotor activity immediately following lights OFF and only gradually (over several minutes) return to baseline locomotor activity. The nrc mutants respond similarly to light OFF as WT fish, but exhibit a slight reduction in their average activity as compared to WT fish. Motor activity in response to light ON in nrc mutants is delayed and sluggish. There is a slow rise time of the nrc mutant response to light ON as compared to WT light ON response. The results indicate that nrc fish are not completely blind. Because teleosts can detect light through non-retinal tissues, we confirmed that the immediate behavioral responses to light-intensity changes require intact eyes by using the chokh (chk) mutants, which completely lack eyes from the earliest stages of development. In our VMR assay, the chk mutants exhibit no startle response to either light ON or OFF, showing that the lateral eyes mediate this behavior. The VMR assay described here complements the well-established OKR assay, which does not test the ability of zebrafish larvae to respond to changes in light intensities. Additionally, the automation of the VMR assay lends itself to high-throughput screening for defects in light-intensity driven visual responses.Download video file.^{(107M, mp4)}     

Functional Richness and Relative Resilience of Bird Communities in Regions with Different Land Use Intensities

Abstract Empirical estimates of the function and resilience of communities under different management regimes can provide valuable information for sustainable natural resource management, but such estimates are scarce to date. We quantified the functional richness and relative resilience of bird communities inhabiting five regions in southeastern Australia that represented different management regimes. First, we show that functional richness and relative resilience were reduced at species-poor sites in all regions. Second, we show that bird communities in agricultural regions had fewer body mass groups and fewer functional groups than expected by chance. This suggests that both the function and the resilience of bird communities in agricultural regions were reduced. The likely mechanisms for the observed loss of function and relative resilience are: (1) the simplification of landscape texture resulting in selective extinction of certain body mass groups; and (2) the selective extinction of certain functional groups that are particularly sensitive to intensive land use. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Assimilation Rate and Growth of Lolium Populations in the Glasshouse in Contrasting Light Intensities

Using growth-analysis techniques, the variation in relativegrowth-rate (RGR) and its components, net assimilation rate(NAR), and leaf-area ratio (LAR), was examined in 18 populationsof L. perenne, six of L. multiflorum, and two hybrid cultivarsfrom contrasting climatic and agronomic origins, grown at lowand high light intensities in the glasshouse. Significant differences between populations were found for RGR,NAR, and LAR at both light intensities. At both intensitiesthe annual or biennial multiflorum group had a greater LAR anda lower specific leaf weight and chlorophyll content than theperennial perenne group. At the low intensity this was compensatedby a greater NAR in the perenne group, with no resultant differencein RGR. At the high intensity there was no difference betweenthe groups in NAR, and hence a greater RGR in the multiflorumgroup. Within the perenne and multiflorum groups, at both light intensities,the variation between populations in RGR was based on differencesin NAR rather than in LAR. There was no regular correlationof NAR with either specific leaf weight, or chlorophyll contentat either light intensity, though at low light intensity itwas significantly correlated with shoot-root ratio.     

Influence of Schistosoma mansoni and Hookworm Infection Intensities on Anaemia in Ugandan Villages

BackgroundThe association of anaemia with intestinal schistosomiasis and hookworm infections are poorly explored in populations that are not limited to children or pregnant women.MethodsWe sampled 1,832 individuals aged 5–90 years from 30 communities in Mayuge District, Uganda. Demographic, village, and parasitological data were collected. Infection risk factors were compared in ordinal logistic regressions. Anaemia and infection intensities were analyzed in multilevel models, and population attributable fractions were estimated.FindingsHousehold and village-level predictors of Schistosoma mansoni and hookworm were opposite in direction or significant for single infections. S. mansoni was found primarily in children, whereas hookworm was prevalent amongst the elderly. Anaemia was more prevalent in individuals with S. mansoni and increased by 2.86 fold (p-value<0.001) with heavy S. mansoni infection intensity. Individuals with heavy hookworm were 1.65 times (p-value = 0.008) more likely to have anaemia than uninfected participants. Amongst individuals with heavy S. mansoni infection intensity, 32.0% (p-value<0.001) of anaemia could be attributed to S. mansoni. For people with heavy hookworm infections, 23.7% (p-value = 0.002) of anaemia could be attributed to hookworm. A greater fraction of anaemia (24.9%, p-value = 0.002) was attributable to heavy hookworm infections in adults (excluding pregnant women) as opposed to heavy hookworm infections in school-aged children and pregnant women (20.2%, p-value = 0.001).ConclusionCommunity-based surveys captured anaemia in children and adults affected by S. mansoni and hookworm infections. For areas endemic with schistosomiasis or hookworm infections, WHO guidelines should include adults for treatment in helminth control programmes.     

The Influence of Habitat Variables on Bird Communities in Forest Remnants in Costa Rica

This study examined the effects of forest structure (tree species richness, canopy height, percent canopy cover, understory density, tree density and DBH) and avian species traits (nest type and indicator list status) on the diversity, abundance and dissimilarity of bird communities in forest remnants and reforestation areas adjacent to Costa Rican banana plantations. Bird species richness and abundance were significantly related to tree species richness, canopy height and canopy cover in multiple linear regressions, the latter two forest structure variables being the best statistical predictors. Stratification of analyses by bird species indicator categories improved fits of regressions, because correlations with environmental variables differed in sign for different guilds of birds, a result likely to hold for other avifaunas. Analysis of avifauna dissimilarities among sites demonstrated that the species composition of bird communities was highly correlated with forest structure and tree species composition. Logistic regressions indicated that birds making protected (cavity, burrow, pendant, sphere and covered) nests were 2–6 times more likely to be present in the study avifauna than birds making open (cup, saucer, platform and scrape) nests and indicators of disturbed habitats were 11 times more likely to be present than indicators of primary forest. The forest structure data used were simple and inexpensive to collect, and data on avian traits were drawn from the literature. Thus, these methods could easily be replicated at other locations and would be valuable management aids and biodiversity assessment tools for conservation planning.     

The Influence of Varying Light Intensities on the Photo-transformation of Protochlorophyllide636 in Dark Grown Wheat Leaves Treated with δ-Aminolevulinic Acid

Leaves treated with δ-aminoievulinic acid accumulate protochlorophyllide₆₃₆ in large amounts. Due to a continuous conversion of protochlorophyllide₆₃₆ (nonphototransformable) into protochlorophyllide₆₅₀ (phototransformable) in weak red light, the photoreduction of protochlorophyllide to chlorophyllide can proceed for at least 20 minutes and results in a chlorophyllide content of the leaves three times higher than that in untreated leaves. The half time for this chlorophyllide accumulation is 55 seconds. A photodestruction of the pigments takes place at high light intensities or if the content of protochlorophyllide₆₃₆ is high. The conversion of protochlorophyllide₆₃₆ to chlorophyllide is dependent on the light intensity used for phototransformation of protochlorophyllide₅₅₀ The conversion of PChlide₆₄₆ was not limiting for chlorophyllide formation within the range of the light intensity used. The extrapolation of a double reciprocal plot of chlorophyllide formation, rate versus light intensity gives a maximal value of 8.7 μg chlorophyllide per g fresh weight and min. The conversion of protochlorophyllide₃₆₃ to protochlorophyllide₆₅₀ is believed to depend on the available sites of an apophotoenzyme.     

Photosynthetic Units and Carbon Assimilation in Leaves of Grain Sorghum under Different Light Intensities

The Cyt f and P700 contents in leaves of three Sorghum, varietieswere measured, in relation to their carbon assimilation, underdifferent light intensities during growth. At the maximum irradiationused (1,800 µE m^–2 s^–1) the ratio of P700to Cyt f was close to unity, whereas under low irradiation (450µE m^–2 s^–1) the ratio of P700 to Cyt f rangedfrom two to three. A strikingly positive correlation existedbetween the P700 contents of the leaves and their rates of carbondioxide fixation, dry matter production and Cyt f contents,only when the plants were grown under high light intensities.The P700 content of the leaves in plants grown under low irradiationwas unrelated to the contents of Cyt f. Thus, at a high lightintensity there is a close relationship between the Cyt f andP700 levels, but at low intensities the amounts of electroncarriers and the reaction centre are independent. (Received March 7, 1983; Accepted August 24, 1983)     

The Influence of Tropical Plant Diversity and Composition on Soil Microbial Communities

There is growing interest in understanding the linkages between above- and belowground communities, and very little is known about these linkages in tropical systems. Using an experimental site at La Selva Biological Station, Costa Rica, we examined whether plant diversity, plant community composition, and season influenced microbial communities. We also determined whether soil characteristics were related to differences in microbial communities. Phospholipid fatty acid (PLFA) composition revealed that microbial community composition differed across a plant diversity gradient (plots contained 1, 3, 5, or over 25 species). Plant species identity also was a factor influencing microbial community composition; PLFA composition significantly varied among monocultures, and among three-species combinations that differed in plant species composition. Differences among treatments within each of these comparisons were apparent in all four sampling dates of the study. There was no consistent shift in microbial community composition between wet and dry seasons, although we did see significant changes over time. Of all measured soil characteristics, soil C/N was most often associated with changes in microbial community composition across treatment groups. Our findings provide evidence for human alteration of soil microbial communities via the alteration of plant community composition and diversity and that such changes are mediated in part by changes in soil carbon quality.     

The Relative Influence of Competition and Prey Defenses on the Phenotypic Structure of Insectivorous Bat Ensembles in Southern Africa

Deterministic filters such as competition and prey defences should have a strong influence on the community structure of animals such as insectivorous bats that have life histories characterized by low fecundity, low predation risk, long life expectancy, and stable populations. We investigated the relative influence of these two deterministic filters on the phenotypic structure of insectivorous bat ensembles in southern Africa. We used null models to simulate the random phenotypic patterns expected in the absence of competition or prey defences and analysed the deviations of the observed phenotypic pattern from these expected random patterns. The phenotypic structure at local scales exhibited non-random patterns consistent with both competition and prey defense hypotheses. There was evidence that competition influenced body size distribution across ensembles. Competition also influenced wing and echolocation patterns in ensembles and in functional foraging groups with high species richness or abundance. At the same time, prey defense filters influenced echolocation patterns in two species-poor ensembles. Non-random patterns remained evident even after we removed the influence of body size from wing morphology and echolocation parameters taking phylogeny into account. However, abiotic filters such as geographic distribution ranges of small and large-bodied species, extinction risk, and the physics of flight and sound probably also interacted with biotic filters at local and/or regional scales to influence the community structure of sympatric bats in southern Africa. Future studies should investigate alternative parameters that define bat community structure such as diet and abundance to better determine the influence of competition and prey defences on the structure of insectivorous bat ensembles in southern Africa.     

光照强度对金果榄光合特性和生长品质的影响

目的:探讨不同光照强度对金果榄植株光合特性和生长的影响.方法:设置光照强度为自然光强的100％、52.7％、33.2％和15.8％四种处理,测定其光合速率等生理指标、叶绿素、生物产量及活性成分含量的变化.结果:1.低光照强度处理的光合速率均高于100％自然光照处理,33.2％处理最高,显著地高于52.7％处理和15.8...     

The Role of Nitrate in the Osmoregulation of Lettuce (Lactuca sativa L.) Grown at Different Light Intensities

Blom-Zandstra, M. and Lampe, J. E. M., 1985. The role of nitratein the osmoregulation of lettuce (Lactuca sativa L.) grown atdifferent light intensities.—J. exp. Bot. 36: 1043–1052. The effect of different light intensities on the nitrate accumulationvis-à-vis the concentration of other solutes in plantsap expressed from lettuce leaves was studied. After growinglettuce plants under constant environmental conditions for 52d, they were transferred to different light intensities andharvested periodically. A quantitative analysis of componentsin solution in the expressed plant sap showed a decrease innitrate concentration and an increase in the organic acids (mainlymalate) and sugars (mainly glucose) with increasing light intensity.The light intensity only slightly increased the osmolarity ofthe expressed plant sap. The measured osmolarity correspondedvery well with the value estimated from the quantitative analysesimplying that all osmotically active compounds had been accountedfor. The decrease in nitrate concentration in the expressedplant sap was fully compensated for by an increase in the dissociatedorganic acids that partly dissociate twofold to sustain electroneutralityand by an increase in both organic acids and sugars to maintainthe osmolarity. The suggestion is supported that nitrate mayserve as osmoticum at low light conditions to compensate forthe shortage of carbohydrates resulting from suboptimal photosynthesis. Key words: Nitrate accumulation, osmoregulation, Lactuca saliva L.     

光强在低温弱光胁迫后番茄叶片光合作用恢复中的作用

为了研究光强在低温弱光胁迫后番茄叶片光合作用恢复中的作用,以番茄品种浙粉202为材料,研究了低温弱光后恢复期全光照与遮荫对光合作用和叶绿素荧光参数的影响。结果表明：低温弱光（8℃/12℃,PFD 80 μmol·m^-2·s^-1）导致番茄叶片P_n、Φ_PSⅡ、qP和F_v′/F_m′的下降,但诱导了NPQ的上升,未引起F_v/F_m的变化;全光照（100%光照）下恢复1 使得植株叶片P_n、F_v/F_m、Φ_PSⅡ、qP、NPQ和F_v′/F_m′均大幅下降,随后光合和荧光参数可缓慢恢复至对照水平;遮荫（40%光照）恢复植株F_v/F_m、Φ_PSⅡ和F_v′/F_m′仅在第一天稍有下降,而P_n和qP还略有上升,NPQ虽有所降低但仍显著高于对照水平,随后光合和荧光参数均可迅速恢复到对照水平。说明低温弱光虽抑制了光合作用的进行,但并未引起光抑制的发生;全光照恢复加剧了叶片光抑制的发生,而遮荫恢复可通过叶片PSⅡ光化学活性的快速恢复和天线色素热耗散能力的增强以保护光合机构免受伤害,有利于光合作用的迅速恢复。