An inter-basin comparison of nutrient limitation and the irradiance response of pulse-amplitude modulated (PAM) fluorescence in Lake Erie phytoplankton

This research examined the application of the maximum quantum efficiency (F _v/F _m) and relative electron transport rate versus irradiance curves (rETR) as a rapid, sensitive assessment of Lake Erie phytoplankton nutrient status. I evaluated the potential benefits of the variable fluorescence parameters by comparing these parameters with chemical and physiological nutrient status assays. I tested the hypothesis that F _v/F _m and rETR curves could diagnose nutrient status in natural lake phytoplankton and be capable of discriminating which inorganic nutrient is limited temporally and spatially. F _v/F _m was on average highest in the more eutrophic west basin (WB) and lowest in the more oligotrophic central basin (CB). According to the chemical and physiological indicators, P deficiency was most severe in the CB during summer stratification and N deficiency was strongest in the WB during isothermal conditions. Like F _v/F _m, rETR at light saturation (rETR_max) and the initial slope of the rETR versus irradiance curve (α) decreased as the severity of N and P deficiency increased. Amendment with N or P stimulated increased F _v/F _m, rETR_max, and α in N- and P-limited samples, respectively, and abolished the photoinhibition apparent in rETR curves of nutrient-limited samples. These results supported the view that the N and P deficiency assays, and corresponding variations of variable fluorescence parameters, were valid indicators of widely variable N and P deficiency in the phytoplankton, and could be used to provide a promising tool in determining phytoplankton nutrient status. Contrary to my hopes, it did not appear that rETR–irradiance curves could discriminate between N and P deficiency. Identification of the most limiting nutrient still demanded additional information beyond the variable fluorescence measurements.     

Effects of temperature and pH on growth and photosynthesis of the thermophilic cyanobacterium Synechococcus lividus as measured by pulse-amplitude modulated fluorometry

In this study, the effects of five different temperatures and pH conditions on growth and photosynthetic performance of Synechococcus lividus Copeland from Taiwan were monitored in the field and the laboratory by using an underwater pulse‐amplitude modulated (Diving‐PAM) fluorometer. In the field, the optimal growth temperature of S. lividus was found to be 57°C. Such a finding was congruent with the growth rate in the laboratory culture, in which the optimal growth temperatures ranged from 45 to 60°C. In photosynthetic performance, the light‐saturated maximum relative electron transport rate (ETR_max) and the light‐limited slope (α^ETR) exhibited highest values at 50°C. At five different pH conditions, higher ETR_max and α^ETR were observed from pH 7 to 9. In addition, regression analysis demonstrated a significant positive relationship between the growth rate and the ETR_max values (R² = 0.9527), indicating that the growth of S. lividus was largely restricted to its photosynthetic performance. In conclusion, the photosynthetic performance and growth of the thermophilic cyanobacterium S. lividus were sensitive to fluctuations in temperature but not in pH. The present investigation offers a better understanding of the photosynthetic physiology.     

Applying Pulse Amplitude Modulation (PAM) fluorometry to microalgae suspensions: stirring potentially impacts fluorescence

The use of microalgae suspensions in PAM-fluorometers such as the Water-PAM (Walz GmbH, Germany) presents the problem of maintaining a homogeneous sample. The Water-PAM is marketed with an optional accessory for stirring the sample within the cuvette while in the emitter–detector (ED) unit. This stirring device can help to prevent cells from settling out of suspension over the time-course of chlorophyll-a fluorescence measurements. The ED unit was found to provide a vertically heterogeneous light environment and, therefore, cells within a single sample can exist in different quenched states. Enhancing cell movement by stirring was found to substantially influence measured fluorescence yield while performing induction curve and rapid light curve analyses. This is likely to result from relatively unquenched cells outside the main light-path moving into a higher light region and thus emitting disproportionately more fluorescence than quenched cells. Samples containing cells with high sinking rates or motile species may encounter similar (but reduced) problems. This effect can be mitigated by: (a) reducing analysis time to minimise the distance cells can sink/swim during the measurement procedure and avoiding the necessity of stirring; (b) limiting the proportion of sample outside the light path by minimising sample volume or; (c) by activating the stirrer only for short periods between saturation pulses and allowing enough time after stirring for quenching to stabilise before activation of the saturation pulse. Alternatively, modifications to the instrument providing a vertical dimension to the LED-array could resolve the issue by providing a more homogeneous light environment for the sample.     

A model for early events in the assembly pathway of cyanobacterial phycobilisomes

Biological self-assembly is remarkable in its fidelity and in the efficient production of intricate molecular machines and functional materials from a heterogeneous mixture of macromolecules. The phycobilisome, a light-harvesting structure of cyanobacteria, presents the opportunity to study an in vivo assembly process in detail. The phycobilisome molecular architecture is defined, and crystal structures are available for all major proteins, as are a large sequence database (including a genome sequence) and effective genetic systems exist for some cyanobacteria. Recent studies on subunit interaction, covalent modification, and protein stability suggest a model for the earliest events in the phycobilisome assembly pathway. Partitioning of phycobilisome proteins between degradation and assembly is proposed to be controlled by the interaction equilibria between phycobilisome assembly partners, processing enzymes and chaperones. The model provides plausible explanations for existing observations and makes predictions that are amenable to direct experimental investigation.     

Biomaterial culture conditions impacting the performance of a PAM fluorometry based aquatic phytotoxicity assay

An aquatic phytotoxicity assay, based on the principles of pulse amplitude modulated (PAM) fluorometry has recently been developed and validated under laboratory conditions. Characteristics of the assay include the use of photosynthesising biomaterial, most frequently whole organism microalgae. The instrument employs light probing measurements to monitor chlorophyll fluorescence signals emitted by the biomaterial component. These characteristics could leave assay performance susceptible to interference by minor variations in biomaterial treatment and culture conditions prior to testing. This study investigates assay performance in response to variations in two microalgae culture parameters; short-term light history (24h) prior to testing and the sterility of long-term culture conditions. Light history of the four microalgal species tested significantly impacted their toxicity response, as measured with the assay. Light treatments of 5 micromol photons m(-2)s(-1) produced the highest photosystem II quantum yields (Phi(II)) whilst higher light intensities resulted in an inverse relationship between Phi(II) and the measured toxicity response (inhibition (%) of photochemistry). Of the two microalgal cultures tested, sterility of culture conditions significantly impacted the performance of the green freshwater algae, Chlorella vulgaris as assay biomaterial. On average 1 microg L(-1) diuron inhibited photochemistry 2.6% less in axenically cultured C. vulgaris compared with non-axenically maintained cultures. This investigation series contributes valuable quality assurance data towards microalgal based PAM fluorometry assays and emphasises the importance of such investigations if new biorecognition systems are to be accredited and/or routinely incorporated for biomonitoring purposes.     

A pulse-amplitude modulated fluorescence-based method for assessing the effects of photosystem II herbicides on freshwater periphyton

A test was developed that measures in vivo chlorophyll afluorescence variables to assess the apparent sensitivity of freshwaterperiphytic algae to photosystem II inhibitors. Natural periphyticcommunities from rivers were collected on artificial substrata, and theeffects of short-term exposures to two PSII herbicides (atrazine andisoproturon) on the fluorescence parameters were measured with apulse-amplitude modulated fluorometer. The EC50 for each herbicide werecalculated from fluorescence yield indices, and these results were comparedto ¹⁴C-based primary production measurements on the samecommunities. The fluorescence-based method appears to give very reliableestimations of EC50 for each pesticide we tested, ranging from 0.46 to5.18 M and 0.07 to 6.77 M for atrazine and isoproturon,respectively. This method could be used in ecotoxicology monitoringprograms, to detect changes in natural periphyton populations sensitivity,following photosystem II herbicide contamination in rivers or lakes.     

Assessment of the impact of photosystem I chlorophyll fluorescence on the pulse-amplitude modulated quenching analysis in leaves of Arabidopsis thaliana

Photosynthesis Research - In their natural environment, plants are exposed to varying light conditions, which can lead to a build-up of excitation energy in photosystem (PS) II. Non-photochemical...     

Multi‐wavelength Pulse Amplitude Modulated fluorometry (Phyto‐PAM) reveals differential effects of ultraviolet radiation on the photosynthetic physiology of phytoplankton pigment groups

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A contribution to the Dicyrtomidae (Collembola) of Hawaii

Ten new species in three subgenera of Dicyrtoma are described from the Hawaiian Islands. Specimens were received from collections made on Hawaii, Maui, Kauai and Oahu. Species definitions are based on chaetotaxy of head, legs and the circumanal region. In addition, presence or absence of lateral spines (neosminthurid setae) on the parafurcular lobes may assist in grouping species within subgenera. Previous records of dicyrtomids from Hawaii include only one species, Ptenothrix ( Papaairioides ) daubia (Folsom). The following new species are described: Ptenothrix ( Ptenothrix ) hawaiicnaeis sp.n., Ptenothrix ( Papirioides ) kauaiensis sp.n., P. ( Papirioides ) serrata sp.n., Dicyrtoma ( Calvatomina ) sylvestratilis sp.n., D. ( Calvatomina ) brevifibra sp.n., D. ( Calvatomina ) tesselata sp.n., D. ( Calvatomina ) longidigita sp.n., D. ( Calvatomina ) bellingeri sp.n., D. ( Calvatomina ) madestris sp.n., and D. ( Calvatomina ) microdentata sp.n.     

Diurnal variation in relative photosynthetic performance in giant kelp Macrocystis pyrifera (Phaeophyceae, Laminariales) at different depths as estimated using PAM fluorometry

Pulse-amplitude modulated (PAM) fluorometry allows instantaneous estimates of photosynthetic rates, but may well produce variable measurements of photosynthetic activity depending on time of day, recent light history, internal fluctuations, and environmental variability. To investigate this, we compare estimates of diurnal variability in relative photosynthetic performance for the giant kelp, Macrocystis pyrifera (L.) C. Agardh, obtained from PAM fluorometry at three depths during 3 days characterized by different light conditions, and for two different blade ages. Sampling in the mid morning, late morning, early afternoon and late afternoon, we examined diurnal changes in relative photosynthetic performance in meristematic tissue and older blades occurring near the bottom, in the mid water, and at the water surface. Measures of maximum relative electron transport rates (rETR_max), minimum saturating irradiance (E_k), photosynthetic efficiency (α) and maximum quantum yield (F_v/F_m) show that giant kelp blades in the mid water and near the bottom exhibit little to no photosynthetic changes during the day. Near the surface, however, blades exhibit photosynthetic characteristics similar to light-adapted species in that they begin the day acclimated to low light, acclimate to increasing irradiance during the day, and end the day acclimated to low light. Consequently, while estimates of rETR_max were highest during the midday for all sample depths and days, they were also always highest near the surface for both old blades (112.16 ± 8.7, 98.6 ± 14.7, 70.16 ± 5.7) and meristematic tissue (109.0 ± 9.0, 86.9 ± 1.9, 59.2 ± 11.6, surface, mid water and bottom, respectively). Similar patterns were observed for E_k for both old blades (169.2 ± 5.4, 88.0 ± 11.2, 83.8 ± 5.2) and meristematic tissue (138.4 ± 11.5, 96.6 ± 4.69, 68.4 ± 10.6). In contrast, estimates of F_v/F_m were lowest near the surface during the midday for both old blades (0.6 ± 0.02, 0.73 ± 0.69, 0.75 ± 0.01) and meristematic tissue (0.58 ± 0.02, 0.69 ± 0.05, 0.74 ± 0.01, surface, mid water and bottom, respectively). These patterns coincided with similar patterns in ambient light, which was most variable and reached its greatest values near the surface during the midday.     

Program oversight enhancements (POE): the big PAM

Federal animal welfare regulations and policies require compliance during animal research. But the methods used to oversee, assess, and ascertain compliance are left in the hands of the research institution and its institutional animal care and use committee (IACUC). Differences in institutional cultures, research goals, individuals responsible for animal care and use activities and oversight, and availability of financial and personnel resources have given rise to a variety of institution-specific mechanisms for ensuring compliance with the federal requirements and specifically with IACUC-approved animal research activities. In recent years one such mechanism, postapproval monitoring (PAM), has risen in popularity. An often cited topic in animal welfare-related conferences and periodicals, it is well on its way to becoming a compliance standard. However, it is but one mechanism for ensuring postapproval compliance and is not required by the federal animal welfare regulations. In this article we describe alternative mechanisms for ensuring compliance with IACUC-approved animal research through the use of program oversight enhancements (POE) in the context of an institution's animal care and use program. We present these enhancements in a way that allows readers to pick and choose those of interest. While these methods may not be feasible at all institutions, adopting even a few should improve a program's ability to ensure compliance with approved animal research and reduce the need for an aggressive and formal postapproval monitoring process.     

Some observations on phycobilisomes of Pterocladiella capillacea (Gelidiaceae,Rhodophyta)

ABSTRACT

Phycobilisomes (PBSs) of the red alga Pterocladiella capillacea collected in the field, were characterized both in situ and in vitro by means of a transmission electron microscope (TEM) and an image analyzer. Ultrathin sections of thalli and negatively stained PBSs after isolation revealed hemi-ellipsoidal shapes. In situ PBS dimensions were 38.5 ± 0.2 nm (height) × 38.8 ± 0.2 nm (width) × 22.6 ± 0.2 nm (thickness) in good agreement with the in vitro measurements (mean diameters of 37.6 ± 0.2 nm). These dimensions, especially the width, are smaller than those so far reported for red algae. This could depend either on the ecophysiological conditions of the thalli when harvested and/or on a staggered, symmetrically rotated and compressed disposition of biliprotein rods with respect to the allophycocyanin (APC) core. Hydroxylapatite chromatography of biliproteic extracts and SDS-PAGE electrophoresis revealed that phycoerythrin type R-(λ_max 565 nm>540 nm>498 nm) is formed by α (18.6 kDa), β (19.9 kDa), γ (30.2kDa) and γ′ (33.8 kDa) sub-units. The presence of two γ sub-units suggests that this phycoerythrin is a set of (αβ)₆γ + (αβ)₆γ′ aggregates (R-PE). A spectroscopically distinct form of phycoerythrin with different peak ratios, also found in pure fractions, is thought to be a polydisperse form (the so called r-PE). Similarity of shape and size observed in PBSs both in situ and in vitro, and fluorescence spectral characteristics of PBSs in vitro would indicate a substantial integrity of isolated PBSs. These measurements, if compared with total biliprotein content, would seem to indicate a PE fraction not assembled into PBS. A possible role of phycoerythrin in relation to the ability for a rapid adaptation of this surface species to environmental changes is suggested.     

On the linkage of exoplasmatic freeze-fracture particles to phycobilisomes

The thylakoids of the thermophilic cyanobacterium Mastigocladus laminosus were examined by freeze-fracture analysis. The expolasmatic (EF)-freeze-fracture particles are organized in rows, separated by 45 nm or more with a 12-nm center-tocenter spacing of neighboring particles. Phycobilisomes, associated to the outer thylakoid surfaces show a similar spacing pattern. Fractures exposing simultaneously phycobilisomes and EF-freeze-fracture particles on the same thylakoid show a direct alignment of both systems. Consequently the phycobilisomes are concluded to be associated peripherally on top of the EF-freeze-fracture particles in a 1:1 assembly pattern. The periodicity of the EF-freeze-fracture particles determines the arrangement of the phycobilisomes in the rows. The planar phycobilisome model of Mörschel et al. (1977) easily allows a successive arrangement of the phycobilisomes in a row, whereas with the staggered model developed by Bryant et al. (1979), only a cogged arrangement of neighboring phycobilisomes is possible.     

The contribution of afferent signals from the liver to metabolic regulation during exercise

The crucial role of the liver as the only organ to produce glucose used by skeletal muscle during exercise is well known. Since hepatic glucose production is central to blood glucose homeostasis during exercise, it has been postulated that the liver may inform the central nervous system and other organs of its diminishing capacity to produce glucose from glycogen, before blood glucose falls. The sensory role of the liver during exercise would be similar to its role in the control of food intake. As a consequence, the experimental approaches used to test the hypothesis that afferent signals from the liver contribute to metabolic regulation during exercise are inspired by those used to test the same hypothesis in the regulation of food intake. In the present review, two questions are addressed. The existing evidence for the liver's sensory influence on metabolic adjustments to exercise is first reviewed; the nature of the initiating stimuli for the afferent contribution of the liver to physical exercise is discussed thereafter. The hypothetical construct upon which rests the contribution of the liver's afferent signals to metabolic regulation during exercise is that a decrease in liver glycogen or a related metabolic intermediate is sensed by the liver, and the signal is transduced to the central nervous system, most likely through the afferent activity of the hepatic vagus nerve, where it contributes to the orchestration of the metabolic and hormonal responses to exercise. Support in favour of this construct comes mainly from the demonstration that sectioning of the hepatic vagus nerve attenuates the normal hormonal response to exercise. It seems that the liver-glucagon axis is particularly responsive to this reflex activation. In other respects, the hepatic mechanism responsible for linking the metabolic activity in the liver to an afferent signal capable of regulating the metabolic response to exercise remains speculative. Substrates or derivatives of substrate oxidation, energy-related compounds (ATP and Pi), or changes in cell volume may all be related to changes in transmembrane potential in the liver cell, which according to the "potentiostatic" theory would determine the afferent vagal activity.     

A contribution to the Sphagnum (Sphagnaceae) flora of Paraguay

The genusSphagnum is reviewed for Paraguay, with an emphasis on recent collections. Five species and one variety are recognized:S. perichaetiale Hampe,S. magellanicum Brid.,S. pulchricoma C. Müll.,S. itabense Crum & Buck, sp. nov.,S. flaccidum Besch., andS. flaccidum var.lindmanii (Warnst.) Warnst.Sphagnum flaccidum is redescribed; it is illustrated, as areS. perichaetiale andS. itabense.     

A serological contribution to the systematics of the genusLupinus (Fabaceae)

The immunological comparison of the seed reserve proteins suggests thatLupinus is a natural genus, the American and the Euro-African species belonging to the same stock. Among the Lupines of the Old World, the smooth-seeded and the rough-seeded species from two natural segregates. The genusLupinus is serologically related to the rest of theGenisteae and to the AsiaticSophoreae rather than to AmericanSophoreae andThermopsideae. The data suggest thatLupinus may have originated with the remainder of theGenisteae from primitiveSophoreae of temperate-subtropical Asia. America and the Mediterranean-African region are regarded as secondary centres of speciation.     

Binding of AP2 to sorting signals is modulated by AP2 phosphorylation

The two clathrin-associated adaptor complexes AP1 and AP2 are known to participate in the formation of clathrin-coated vesicles at the trans-Golgi network and at the plasma membrane. During this process adaptors are involved in the sequestration of vesicle cargo by binding to the sorting signals within the cytoplasmic domains of the cargo proteins and in the recruitment of the clathrin coat. After budding of the clathrin-coated vesicles, the clathrin and adaptors dissociate from the vesicles. Here we show that in vitro binding of AP2 to sorting signals, which is one of the initial steps in receptor-mediated endocytosis, is modulated by adaptor phosphorylation. AP2 was phosphorylated by incubating purified AP2 in the presence of ATP and dephosphorylated by incubation with alkaline phosphatase. Affinity for tyrosine-, leucine-based and noncanonical sorting motifs was 15-33 times higher for phosphorylated than for dephosphorylated AP2. Also the binding of AP2 to membranes was regulated by adaptor phosphorylation/dephosphorylation and was about 8-fold higher for phosphorylated than for dephosphorylated AP2. Moreover, AP2 isolated from cytosol is higher phosphorylated than membrane-extracted and exhibits a 5-fold higher binding affinity than AP2 extracted from membranes. Taken together these data point to a cycle of phosphorylation/dephosphorylation as a mechanism for regulating the reversible association of AP2 with membranes and sorting signals during the process of receptor-mediated endocytosis.     

PhyloSort: a user-friendly phylogenetic sorting tool and its application to estimating the cyanobacterial contribution to the nuclear genome of Chlamydomonas

Background

Molecular phylogenetic analyses have identified Trimeniaceae, a monotypic family distributed only in Oceania, as among the earliest diverging families of extant angiosperms. Therefore, the fossils of this family are helpful to understand the earliest flowering plants. Paleobotanical information is also important to track the historical and geographical pathways to endemism of the Trimeniaceae. However, fossils of the family were previously unknown from the Early Cretaceous, the time when the angiosperm radiated. In this study, we report a seed from the late Albian (ca. 100 million years ago) of Japan representing the oldest known occurrence of Trimeniaceae and discuss the character evolution and biogeography of this family.

Results

A structurally preserved seed was collected from the early Late Albian Hikagenosawa Formation of the Yezo Group, which was deposited in palaeolatitudes of 35 to 40°N. The seed has a multilayered stony exotesta with alveolate surface, parenchymatous mesotesta, and operculate inner integument, which are characteristic to extant trimeniaceous seeds. However, the seed differs from extant seeds, i.e., in its well-developed endosperm and absence of antiraphal vascular bundle. Thus, the seed would be a new genus and species of Trimeniaceae.

Conclusion

The fossil seed indicates that seed coat characters were conserved for 100 million years or more in Trimeniaceae. It also suggests that the antiraphal vascular bundle and perispermy originated secondarily in Trimeniaceae as previously inferred from the phylogeny and character distribution in the extant basalmost angiosperms. The fossil seed provides the first evidence that Trimeniaceae was distributed in a midlatitude location of the Northern Hemisphere during the Early Cretaceous, when angiosperms radiated extensively, supporting a hypothesis that the extant austral distribution is relict.     

Resolving the Azorean knot: a response to Carine & Schaefer (2010)

Carine & Schaefer (Journal of Biogeography, 2010, 37 , 77–89) suggest that the lack of past climate oscillations in the Azores may have contributed to the low plant endemism in this archipelago compared to that of the Canary Islands, a pattern they term the Azorean diversity enigma. Here we challenge their hypothesis, and discuss how the particular characteristics of the Azores may have driven current diversification patterns in this archipelago. We argue that the restricted number of Azorean endemic species and their wide distribution is explicable by the geological, geographical and ecological attributes of the archipelago. That is, the Azores are too young, too small, and too environmentally homogeneous to have hosted many in situ diversification events, so they do not host as many endemic species as other Macaronesian archipelagos, such as Madeira and especially the Canary Islands.