Chara Fragilis Research Articles

On the mechanism of uranium binding to cell wall of Chara fragilis

Biosorption of uranium from nuclear waste liquids and contaminated surface waters and soils has recently attracted special interest. However, the detailed mechanism of uranium uptake by plants is not well understood. The aim of this work is to investigate the role of cell wall components of the freshwater alga Chara fragilis in uranium sequestration from its solution. Three types of algae preparations: extract of cell wall polysaccharides, dried and live algae were subjected to uranium solutions of different concentration and pH. FTIR and X-ray diffraction were used to assess both potential binding sites and the form of the uranyl sequestered by algae. Sorption of uranium by live and dry algae shows remarkable differences both in terms of overall uptake and mechanisms involved. All experiments are consistent with the conclusion that coprecipitation of uranyl species with CaCO3 is the major binding mechanism in uranium sequestration by Chara fragilis, while the direct exchange of Ca2+ with UO22+ has a minor role. Live algae are twice as efficient in sequestering uranium from solution than dried ones due to the formation of different crystalline forms such as aragonite and rutherfordine forming in live algae in the presence of the uranyl species in solution. It therefore appears that metabolic processes such as photosynthesis, most likely through the regulation of pH, play a key role in the uranium uptake by plants. Further understanding of the complex mechanism of metabolic control of the uranium uptake by plants is needed before the planning of bioremediation of this element.

Microbodies of the alga Chara.

Chara fragilis possesses microbodies with a remarkably large size of up to 2 micro m in diameter. Many of the organelles contain huge nucleoids of amorphous material or paracrystalline inclusions. After isolation of the organelles by gradient centrifugation the specific density of the microbodies was determined to be 1.25 g cm-3. Catalase, glycolate oxidase and hydroxypyruvate reductase as well as enzymes of the fatty acid beta-oxidation pathway were demonstrated to be constituents of the microbodies in Chara indicating that they are similar to those in green leaves. The data obtained are in agreement with the view that the Charophyceae and especially the algae in the subgroup of Charales are very closely related to the land plants.

Tradeoff between foraging and antipredator behaviour in a macrophyte dwelling ostracod

The ostracod Cypridopsis vidua is a highly mobile crustacean which frequently occurs in beds of submerged macrophytes in lakes or ponds. A laboratory experiment consisting of eight different treatments was performed to test if this species responds to fluctuations in predation risk, food abundance, hunger, and plant structure by trading off conflicting demands such as searching for food in the sheltered lower zone of a macrophyte or shifting to nutritionally more rewarding patches in the exposed upper zone of this plant. Stems of the macrophyte Chara fragilis covered with a variable amount of periphyton were used as plant structures. To signal predation risk, chemical stimuli derived from tanks containing cyprinid fish were used. The ostracods responded to predator signals by spending significantly more time in the lower zone of the aquaria and by increasing swimming activity especially during the initial phase of encountering the signals. Both with increased hunger level and high food abundance the time spent on Chara increased. When only a single stem of Cham was offered, time spent swimming in the lower zone of the aquarium increased markedly compared to the presence of three stems. In response to different predation risk and food abundance, C. vidua ostracods performed shifts in their vertical microhabitat use as a result of a tradeoff between foraging and antipredator demands. In three experimental treatments the ostracods showed considerable temporal variations in microhabitat choice indicating additional behavioural fine-tuning after a quick preliminary adjustment. In agreement with earlier experimental studies our data support the conclusion that these phytophilous crustaceans are characterized by a well developed capability for exploring their surroundings and by responding to external and internal factors in a flexible and behaviourally dynamic manner.

Negative gravitropism in Chara protonemata: a model integrating the opposite gravitropic responses of protonemata and rhizoids.

The unicellular protonema of Chara fragilis Desv. was investigated in order to establish a reaction chain for negative gravitropism in tip-growing cells. The time course of gravitropic bending after stimulation at angles of 45 degrees or 90 degrees showed three distinct phases of graviresponse. During the first hour after onset of stimulation a strong upward shift of the tip took place. This initial response was followed by an interval of almost straight growth. Complete reorientation was achieved in a third phase with very low bending rates. Gravitropic reorientation could be completely abolished by basipetal centrifugation of the cells, which lastingly removed conspicuous dark organelles from the protonema tip, thus identifying them as statoliths. Within minutes after onset of gravistimulation most or all statoliths were transported acropetally from their resting position 20-100 micrometers from the cell apex to the lower side of the apical dome. This transport is actin-dependent since it could be inhibited with cytochalasin B. Within minutes after arrival of the statoliths, the apical dome flattened on its lower side and bulged on the upper one. After this massive initial response the statoliths remained firmly sedimented, but the distance between this sedimented complex and the cell vertex increased from 7 micrometers to 22 micrometers during the first hour of stimulation and bending rates sharply declined. From this it is concluded that only statoliths inside the apical dome convey information about the spatial orientation of the cell in the gravitropic reaction chain. After inversion of the protonema the statoliths transiently arranged into a disk-shaped complex about 8 micrometers above the vertex. When this statolith complex tilted towards one side of the apical dome, growth was shifted in the opposite direction and bending started. It is argued that the statoliths intruding into the apical dome may displace a growth-organizing structure from its symmetrical position in the apex and may thus cause bending by bulging. In the positively gravitropic Chara rhizoids only a more stable anchorage of the growth-organizing structure is required. As a consequence, sedimented statoliths cannot dislocate this structure from the vertex. Instead they obstruct a symmetrical distribution of cell-wall-forming vesicles around the structure and thus cause bending by bowing.

Adaptive responses in Cypridopsis vidua (Crustacea: Ostracoda) to food and shelter offered by a macrophyte (Chara fragilis)

The ostracod Cypridopsis vidua prefers periphyton growing on Chara fragilis to other feeding substrates. This species actively searches for periphyton, scrapes it off from Chara stems and handles it with a well organized feeding technique. When exposed to different quantities of periphyton on Chara stems, C. vidua selects foraging sites according to their nutritional value. When exposed to low quantities of water from tanks containing fish, C. vidua responds to these weak chemical cues moving from uncovered areas into Chara plants. Experiments with juvenile cyprinids (Abramis brama) as predators and C. vidua as prey clearly showed that the presence of Chara reduces fish foraging success and that C. vidua survival rate increases with increasing density of Chara.

Cytosolic Ca2+‐Concentrations and Distributions in Rhizoids of Chara fragilis Desv. Determined by Ratio Analysis of the Fluorescent Probe Indo‐1

AbstractRhizoids of Charafragilis Desv. were iontophoretically loaded with the Ca2+‐sensitive ratio dye indo‐1. After loading, the rhizoids regained their preinjection‐membrane potential within 2 to 5 min and survived the procedure for more than 24 h, but their growth in length was permanently inhibited. Microfluorimetric measurements of the indo‐1 fluorescence‐ratio showed spontaneous fluctuations of the cytoplasmic Ca2+‐concentration, usually declining from high values after loading to 425 ± 80 nM (± SD, n = 7) as determined by in‐vitro calibration. Increasing the extracellular K+‐concentration (0.1 mM to 10 mM) or Ca2+‐concentration (1 mM to 10 mM) led to increases of 100 to 200 nM in cytoplasmic Ca2+‐concentration. The spatial distribution of cytosolic Ca2+ in the rhizoid tips was visualised in ratio images computed from low‐light video‐pictures. These images showed a fairly homogeneous distribution of Ca2+ throughout the tip cytoplasm with concentrations being in the same range as determined by microfluorimetry. A tip‐to‐base gradient in cytoplasmic Ca2+, thought to be a prerequisite for cell polarity and tip growth, was found in only 1 out of 16 successfully microinjected cells. Additionally, a progressive compartmentalization of the fluorochrome indo‐1, probably in the proplastids and the very abundant endoplasmic reticulum of the rhizoids, was observed.

Exploration of interstitial habitats by the phytophilous Ostracod Cypridopsis vidua (O.F. Müller) : experimental evidence

Cypridopsis vidua (O.F.M.) lives within dense stands of Chara fragilis Desv. in Mondsee. The species develops fast and is very voracious, feeding on the Aufwuchs of the Chara stems. Under experimental conditions, C. vidua actively explores the interstitial of a fine gravel sediment. The ostracodes are also able to find their way out of the interstitial labyrinth. The limited colonisation of deep groundwater habitats by C. vidua (e.g. in the Danube and the Rhone valleys the species lives in superficial alluvial sediments located near the bottom of surface waters) is presumably due to its high energetic requirements. C. vidua recognises the chemical alarm signals of predators such as the fish Abramis brama (L.) ; the ostracods react by drecreasing their motility in both the surface and the interstitial habitat.

Statoliths and microfilaments in plant cells.

Microfilaments have been demonstrated in rhizoids of Chara fragilis Desvaux by labelling of actin with rhodamine-conjugated phalloidin. Each rhizoid contains thick microfilament-bundles arranged longitudinally in the basal region. In the subapical and apical regions, much thinner bundles exist which contact the statoliths and encircle them in the form of a dense envelope. In root statocytes from Lepidium sativum L. the presence of an actin network is indicated by the fact that application of cytochalasin B (25 micrograms ml-1 for 4 h) results in an approximately threefold increase in the rate of statolith (amyloplast) sedimentation relative to controls. It is concluded that in gravity-perceiving plant cells statoliths may trigger the transduction mechanism via actin filaments.

In-vivo observations of a spherical aggregate of endoplasmic reticulum and of Golgi vesicles in the tip of fast-growing Chara rhizoids

In-vivo differential interference contrast microscopy was used to detect individual Golgi vesicles and a new structure in the tip of fast-growing rhizoids of Chara fragilis Desvaux. This structure is a spherical clear zone which is free of Golgi vesicles, has a diameter of 5 μm and is positioned in the center of the apical Golgi-vesicle accumulation ("Spitzenkörper"). After glutaraldehyde fixation and osmium tetroxide-potassium ferricyanide staining of the rhizoid, followed by serial sectioning and three-dimensional reconstruction, the spherical zone shows a tight accumulation of anastomosing endoplasmic reticulum (ER) membranes. The ER membranes radiate from this aggregate towards the apical plasmalemma and to the membranes of the statolith compartments. Upon gravistimulation the ER aggregate changes its position according to the new growth direction, indicating its participation in growth determination. After treatment of the rhizoid with cytochalasin B or phalloidin the ER aggregate disappears and the statoliths sediment. It is concluded that the integrity of the ER aggregate is actin-dependent and that it is related to the polar organisation of the gravitropically growing cell tip.

Morphometry, Primary productivity and Energy flow in a Tropical Pond

Monthly changes in the morphometric features of pond Idumban reveal that total and littoral areas progressively decreased from 62.4 and 15.4 ha in October-November-December to 6.8 and 2.6 ha in September. The dominant macrophytic producers in the littoral area of the pond were Chara fragilis, Hydrilla verticillata and Ceratophyllum demersum, which flourished from October for a period of 8 to 10 months, exhibiting a typical exponential or ‘J’-shaped population growth curve. Biomass of Ch. fragilis increased to the maximum of about 420 g dry weight/m2 in April, H. verticillata to 260 g/m2 in June–July and that of Ce. demersum to 140 g/m2 in April–May. In terms of unit weight, H. verticillata proved to be the most efficient, producing 156 mg dry substance/g plant/day; however, the mean values obtained for 1973-74 were 93, 54 and 53 mg/g/day for H. verticillata, Ch. fragilis and Ce. demersum; the corresponding NPP values 50, 29 and 30 mg/g/day. The GPP and NPP values, expressed in g dry weight/m2/day, were 7 and 4 for H. verticillata, 8 and 4 for Ch. fragilis, 3 and 2 for Ce. demersum. These values, expressed in mg C/m2/day, averaged to 8.2 and 4.6 for all the macrophytes and suggest that the macrophytes were photosynthetically faster and more efficient than phytoplankton. Total gross productivity for Idumban pond amounts to 1773 and 1449 ton (dry weight) for 1973 and 74, respectively: the corresponding values for the NPP were 953 and 825 ton. In other words, 44% of the GPP is lost on plant respiration. Plants equivalent to 56 ton (6% of NPP) are exposed to death in the periphery of the littoral area. The population of Pila globosa proved to be the dominant consumer of these macrophytes. Mean predation amounted to 64 ton/annum for Pila and 200 ton/ annum for other consumer animals. Solar energy known to enter the pond is 1,956,000 Kcal/m2/year. Of this, 24,682 Kcal/m2/year was fixed by the macrophytes, i.e. the photosynthetic efficiency is 1.3%. Of the total GPP, NPP amounted to 13,696 Kcal/m2/year; the net primary production efficiency is 56%. Consumption of the macrophytes by Pila population amounted to 2,943 Kcal/m year and the exploitation efficiency is only 21%.

The Possible Role of Chara fragilis in Mosquito Control

The Possible Role of <i>Chara fragilis</i> in Mosquito Control

Further Studies on Chara Spp. and Other Aquatic Plants in Relation to Mosquito Breeding 1

The study of the effects of Chara fragilis (fig. 1) on mosquito development reported in 1928 (6) has been continued and expanded during the past season. Our investigations were directed along five principal lines: (a) Continued studies of the effects of Chara fragilis on larval development under experimental conditions. (b) A survey of a portion of the central New York area to determine the distribution of Chara spp. and their effect on mosquito density. (c) The introduction of Chara fragilis into various types of ponds, marshes, etc., to study its rate of growth and effect on future mosquito breeding. (d) A continued study of the food 2 (plankton) in Chara ponds and typical mosquito breeding pools. (e) The effects of other aquatic plants on the larvae of Culicidae. The results of this season's work can be presented best under these five headings. Experimental Work With Chara Spp.

A Preliminary Account of the Influence of Light and Temperature on Growth and Reproduction in Chara fragilis

A Preliminary Account of the Influence of Light and Temperature on Growth and Reproduction in Chara fragilis