Datos preliminares sobre el papel del venado cola blanca Odocoileus virginianus (Artiodactyla: Cervidae) como dispersor de semillas

El papel del venado cola blanca como dispersor endozoócoro de semillas se evaluó a través de la estimación del número de semillas y especies encontradas en las muestras fecales, y el análisis del efecto del paso por el tracto digestivo sobre el porcentaje y la velocidad de germinación en semillas de una especie focal (Acacia schaffneri). En total se encontraron 369 semillas en 98 grupos de pellets. La mayoría de las semillas se apreciaban dañadas o inmaduras, sólo 67 semillas (31 morfoespecies) germinaron. El porcentaje de germinación de semillas de A. schaffneri defecadas tendió a ser mayor que la germinación de semillas control. En nuestro estudio el venado figura como depredador de semillas y ocasionalmente como dispersor de semillas. Sin embargo, nuestros resultados con animales en cautiverio muestran que el venado puede incrementar el porcentaje de germinación de algunas especies.The role of white-tailed deer in endozoochorus seed dispersal was evaluated by estimating the number of seeds and seed species found in fecal samples and assessing the effect of gut passage on germination percentage and speed for a focal seed species (Acacia schaffneri). A total of 369 seeds were found in 98 pellet groups. Most seeds appeared to be damaged or immature, and only 67 seeds (31 morphospecies) germinated. Germination percentage of defecated seeds of A. schaffneri tended to be higher than germination of control seeds. In our study site white-tailed deer appears to be acting mainly as a seed predator for ingested seeds, and occasionally as a seed disperser. Nevertheless, our results using captive animals suggest that white-tailed deer may improve seed germination of particular plant species

Effects of Nanomolar Cadmium Concentrations on Water Plants – Comparison of Biochemical and Biophysical Mechanisms of Toxicity Under Environmentally Relevant Conditions

In this thesis, the effects of the highly toxic heavy metal cadmium (Cd) on the rootless aquatic model plant Ceratophyllum demersum are investigated on the biochemical and biophysical level. The experiments were carried out using environmentally relevant conditions, i.e. light and temperature followed a sinusoidal cycle, a low biomass to water ratio resembled the situation in oligotrophic lakes and a continuous exchange of the defined nutrient solution ensured that metal uptake into the plant was not limited by the nutrient solution, but the capacity of the plant. Above all, Cd concentrations in the nanomolar range were applied and experiments lasted long enough to observe chronic toxicity. The toxicity study revealed that the first site of inhibition was the photosynthetic apparatus. The maximal quantum efficiency of photosystem II (PS II) photochemistry in dark adapted state as well as the PS II operating efficiency in actinic light were the first parameters to be reduced. Only afterwards, an increase in reactive oxygen species (ROS) was observed, indicating that they are the result and not the cause of dysfunctional photosynthesis. For most affected parameters, the respective threshold concentration of inhibition or upregulation due to Cd treatment was 20 nM. This is a much lower concentration than applied in many previous studies. All of the observed effects were more pronounced in plants subjected to Cd stress under high light conditions compared to low light conditions, suggesting a protective role of the comparatively larger antenna system of low light grown plants. Cadmium treatment led to a redistribution of other metals, especially Zn in the tissue of C. demersum as revealed using the non-invasive technique of micro X ray fluorescence (µ XRF) on frozen hydrated leaves. At low Cd concentrations, Zn was found mainly in the epidermis and in the mesophyll. At moderately toxic Cd concentration (20 nM), a higher proportion of Zn was found in the mesophyll. At the highest Cd concentrations, Zn was seemingly stuck in the vein, suggesting that the Zn-exporters were blocked by Cd. As part of the detoxification process, a changing distribution of Cd with increasing Cd concentrations was observed. No Cd was detected in the plants from the control treatment (no Cd added) and a homogenous distribution of Cd all over the leaf section was revealed at low Cd treatment. However, at moderately toxic and highly toxic Cd concentrations, sequestration of Cd into specific organs and tissues was observed. The process of sequestration, transport and storage of the toxic metal is already known from hyperaccumulator plants. It usually results in metal storage in organs and tissues where it interferes least with the sensitive metabolic processes like photosynthesis and respiration, i.e. the vein and the epidermis. Another detoxification mechanism was induced upon Cd treatment in C. demersum: the metal-chelating ligands phytochelatins (PCs) were detected in extracts from the plants. The induction of different PCs was not proportional to the applied Cd concentration, but occurred in a switch-like manner and specifically for each PC species. The most noticeable increase was PC3 at the threshold concentration of 20 nM Cd. A combination of different heavy metals and other factors caused the nearly complete lack of macrophytes in an oligotrophic hard water lake (lake Ammelshain). Within the lake, elevated concentrations of Cd (3 nM), Nickel (300 nM) and reduced Phosphate (75 nM) seemed to be responsible for the lack of aquatic plants and were tested for their inhibitory capability in hard and soft water. While the single treatments with non-toxic concentrations of Cd or slightly toxic concentrations of Ni caused no or only minimal toxicity symptoms in C. demersum, they became highly toxic when applied in combination. This negative effect was even more severe under phosphate-limitation. High concentrations of Calcium and Magnesium in the lake water reduced metal toxicity, indicating additional reasons for the absence of macrophytes in the lake. But regarding other freshwater habitats, these measurements revealed that synergistic metal toxicity may be an important influencing factor for the colonisation of soft waters by water plants. Altogether, the results from this thesis indicate the onset of Cd toxicity and detoxification in a model water plant at a significantly lower level than shown in previous studies

Lisss: Lightweight Selfcut Stealth Screw

Vortrag beim Treffen BIG Werkstofftechnik (Bodensee-Interessengemeinschaft Werkstofftechnik), Hochschule Furtwangen, 25.04.201

Acclimation of Trichodesmium erythraeum ISM101 to high and low irradiance analysed on the physiological, biophysical and biochemical level

As the nonheterocystous diazotrophic cyanobacterium Trichodesmium lives both at the ocean surface and deep in the water column, it has to acclimate to vastly different irradiances. Here, we investigate its strategy of light acclimation in several ways.In this study, we used spectrally resolved fluorescence kinetic microscopy to investigate the biophysics of photosynthesis in individual cells, analysed cell extracts for pigment and phycobiliprotein composition, measured nitrogenase activity and the abundance of key proteins, and assayed protein synthesis/degradation by radioactive labelling.After acclimation to high light, Trichodesmium grew faster at 1000 μmol m-2 than at 100 μmol m-2 S-1. This acclimation was associated with decreasing cell diameter, faster protein turnover, the down-regulation of light-harvesting pigments and the outer part of the phycobiliprotein antenna, the up-regUlation of light-protective carotenoids, changes in the coupling of phycobilisomes to thereaction centres and in the coupling of individual phycobiliproteins to the phycobilisomes. The latter was particularly interesting, as it represents an as yet unreported light acclimation strategy.Only in the low light-acclimated culture and only after the onset of actinic light did phycourobilin and phycoerythrin contribute to photochemical fluorescence quenching, showing that these phycobiliproteins may become quickly (in seconds) very closely coupled to photosystem 11. This fast reversible coupling also became visible in the nonphotochemical changes of the fluorescence quantum yield

Analysis of sublethal arsenic toxicity to Ceratophyllum demersum : subcellular distribution of arsenic and inhibition of chlorophyll biosynthesis

Arsenic (As) pollution is a serious concern worldwide. Recent studies under environmentally relevant conditionsrevealed that, in the aquatic plant Ceratophyllum demersum, pigments are the first observable target of toxicity,prior to any effect on photosynthetic parameters or to oxidative stress. Lethal toxicity was initiated by a changeof As species and their distribution pattern in various tissues. Here, the localization of As was investigated at thesubcellular level through X-ray fluorescence using a submicron beam and a Maia detector. Further, it was possibleto obtain useful tissue structural information from the ratio of the tomogram of photon flux behind the sample tothe tomogram of Compton scattering. The micro-X-ray fluorescence tomograms showed that As predominantlyaccumulated in the nucleus of the epidermal cells in young mature leaves exposed to sublethal 1 μM As. Thissuggests that As may exert toxic effects in the nucleus, for example, by interfering with nucleic acid synthesis byreplacing phosphorous with As. At higher cellular concentrations, As was mainly stored in the vacuole, particularlyin mature leaves. An analysis of precursors of chlorophyll and degradation metabolites revealed that the observeddecrease in chlorophyll concentration was associated with hindered biosynthesis, and was not due to degradation.Coproporphyrinogen III could not be detected after exposure to only 0.5 μM As. Levels of subsequent precursors,for example, protoporphyrin IX, Mg-protoporphyrin, Mg-protoporphyrin methyl ester, and divinyl protochlorophyllide,were significantly decreased at this concentration as well, indicating that the pathway was blocked upstreamof tetrapyrrole synthesis

Reversible coupling of individual phycobiliprotein isoforms during state transitions in the cyanobacterium Trichodesmium analysed by single-cell fluorescence kinetic measurements

In the non-heterocyst. marine cyanobacterium Trichodesmium nitrogen fixation is con fined to the photoperiod and occurs coevally with oxygenic photosynthesis although nitrogenase is irreversibly inactivated by oxygen. In previous studies it was found that regulation of photosynthesis for nitrogen fixation involves Mehler reaction and various activity states with reversible coupling of photosynthetic components. We now investigated these activity states in more detail. Spectrally resolved fluorescence kinetic measurements of single cells revealed that they were related to alternate uncoupling and coupling of phycobilisomes from and to the photosystems. changing the effective cross-section of PSI!. Therefore, we isolated and purified the phycobiliproteins of Trichodesmium via ion exchange chromatography and recorded their UV/VIS absorption. fluorescence excitation and fluorescence emission spectra. After describing these spectra by mathematical equations via the Gauss-Peak-Spectra method. we used them to deconvolute the in vivo fluorescence spectra of richodesmium cells. This revealed that the contribution of different parts of the phycobilisome antenna to fluorescence quenching changed during the daily activity cycle. and that individual phycobiliproteins can be reversibly coupled to the photosystems, while the expression levels of these proteins did not change much during the daily activity cycle. Thus we propose that variable phycobilisome coupling plays a key role in the regulation of photosynthesis for nitrogen fixation in Trichodesmium

Different strategies of cadmium detoxification in the submerged macrophyte Ceratophyllum demersum L.

The heavy metal cadmium (Cd) is highly toxic to plants. To understand the mechanisms of tolerance and resistance to Cd, we treated the rootless, submerged macrophyte Ceratophyllum demersum L. with sub-micromolar concentrations of Cd under environmentally relevant conditions. X-ray fluorescence measurements revealed changing distribution patterns of Cd and Zn at non-toxic (0.2 nM, 2 nM), moderately toxic (20 nM) and highly toxic (200 nM) levels of Cd. Increasing Cd concentrations led to enhanced sequestration of Cd into non-photosynthetic tissues like epidermis and vein. At toxic Cd concentrations, Zn was redistributed and mainly found in the vein. Cd treatment induced the synthesis of phytochelatins (PCs) in the plants, with a threshold of induction already at 20 nM Cd for PC3. In comparison, in plants treated with Cu, elevated PC levels were detected only at the highest concentrations (100–200 nM Cu). Our results show that also non-accumulators like C. demersum store toxic metals in tissues where the heavy metal interferes least with metabolic pathways, but remaining toxicity interferes with micronutrient distribution. Furthermore, we found that the induction of phytochelatins is not proportional to metal concentration, but has a distinct threshold, specific for each PC species. Finally we could show that 20 nM Cd, which was previously regarded as non-toxic to most plants, already induces detoxifying mechanisms

MicroX-ray absorption near edge structure tomography reveals cell-specific changes of Zn ligands in leaves of turnip yellow mosaic virus infected plants

As many metals are essential for plants, excess or deficiency of them or alteration of their uptake, translocation, sequestration or physiological use can have severe consequences for plant growth and fitness. Therefore, investigating the distribution and speciation of metals in tissues is essential to understand plant physiology. We present a method based on non-destructive Synchrotron X-ray microtomography combined with microspectroscopy for studying metal distribution and speciation in plant tissues. By using the Maia detector system and the high flux of the undulator beam at the P06 beamline of the PETRA III synchrotron (at DESY), it was possible to record micro X-ray Absorption Near Edge Structure (μXANES) for every voxel of a tomogram. The metal coordination in regions of interest within the tissue samples could be determined by comparing the XANES with spectra of relevant reference compounds. Metal distribution and coordination were measured in shock frozen hydrated plant leaves in a cryostream, avoiding sample preparation artefacts like liquid cell content redistribution that occurs with other preparation methods, unequal distribution of stains in staining assays, sample degradation by beam damage and thawing, etc. A spatial resolution of 5 μm was selected, which is sufficient to resolve all leaf tissues (epidermis, palisade mesophyll, spongy mesophyll, veins), larger cells and biomineralization hotspots.As an application example, we studied the effect of infection with Turnip Yellow Mosaic Virus (TYMV) on the Zn distribution and the Zn speciation in duplicates of Noccaea ochroleucum. This non-accumulator plant grown with 100 μM Zn had enough metal to allow collecting significant spectroscopic data. We found that the TYMV infected samples formed biomineralization crystallites, showing strong spectroscopic similarity to Zn silicate

Sublethal and lethal Cd toxicity in soybean roots specifically affects the metabolome, Cd binding to proteins and cellular distribution of Cd

Soybean (Glycine max (L.) Merr.) plants were exposed to various Cd concentrations from background and low non-toxic (0.5–50 nM) via sublethally toxic (< 550 nM) to highly, ultimately lethally toxic (3 µM) concentrations. Plants were cultivated hydroponically for 10 weeks until pod development stage of the control plants. The threshold and mechanism of sublethal Cd toxicity was investigated by metabolomics and metalloproteomics (HPLC-ICP-MS) measuring metal binding to proteins in the harvested roots. Spatial distribution of Cd was revealed by µXRF-CT. Specific binding of Cd to proteins already at 50 nM Cd revealed the likely high-affinity protein binding targets in roots, identified by protein purification from natural abundance. This revealed allantoinase, aquaporins, peroxidases and protein disulfide isomerase as the most likely high-affinity targets of Cd binding. Cd was deposited in cortex cell vacuoles at sublethal and bound to the cell walls of the outer cortex and the vascular bundle at lethal Cd. Cd binding to proteins likely inhibits them, and possibly induces detoxification mechanisms, as verified by metabolomics: allantoic acid and allantoate increased due to sublethal Cd toxicity. Changes of the Cd binding pattern indicated a detoxification strategy at lower Cd, but saturated binding sites at higher Cd concentrations