Carbonic Anhydrase-Dependent Inorganic Carbon Uptake by the Red Macroalga, Chondrus crispus

The rate of photosynthetic carbon uptake of Chondrus crispus Stack-house plants, at various CO₂ concentrations and pretreated with carbonic anhydrase (CA) inhibitors, was determined using an air-suspension, differential infra-red gas analyzer technique. It was found that the CA inhibitors, acetazolamide, dextran-bound acetazolamide (DBI, which does not permeate cell membranes), and subtilisin (a protease that attacks the cell surface) inhibit photosynthetic carbon uptake in C. crispus. Inhibition was greatest at low CO₂ concentrations, and decreased at CO₂ saturation. Acetazolamide inhibited carbon uptake to a greater extent than DBI. The data support the conclusion that C. crispus plants utilize HCO₃⁻ for photosynthesis, and that both cell-surface and internal CA are involved in the photosynthetic uptake of inorganic carbon.     

Preferential Photosynthetic Uptake of Exogenous HCO(3) in the Marine Macroalga Chondrus crispus

The rate of HCO₃⁻ uptake by the red macroalga Chondrus crispus has been investigated. Unbalanced concentrations of free CO₂ and HCO₃⁻, generated by the photosynthetic activity, were detected in steady state conditions by using an exchange column apparatus linked to an assimilation chamber. Observing the variations of this gradient as influenced by the time of seawater transit from the assimilation chamber towards the column allowed an experimental determination of: (a) the actual gradient created by the photosynthetic activity, (b) the rate constant of the chemical conversion of free CO₂ to HCO₃⁻. With a value of 0.115 per second at pH 8.92, this rate constant was in good agreement with a previous estimation. By using a simple model, we show that the photosynthetic rate of HCO₃⁻ consumption can be estimated by the product of the actual gradient and the rate constant. In the conditions of the experiments reported here, this rate represented more than 90% of the whole photosynthetic flux.     

Oxygen Uptake and Photosynthesis of the Red Macroalga, Chondrus crispus, in Seawater: Effects of Oxygen Concentration

With an experimental system developed for aquatic plants using the mass spectrometry technique and infrared gas analysis of CO₂, we studied the responses to various O₂ concentrations of gas exchanges with the red macroalga Chondrus crispus S. The results were as follows. (a) Irrespective of the CO₂ concentration, net photosynthesis was O₂ sensitive with a 45 to 70% stimulation at 2% O₂. Even with high CO₂, a significant Warburg effect was detected. (b) Although photosynthesis was CO₂ sensitive, O₂ photoconsumption was only weakly affected by CO₂ even at high CO₂ where it was still photodependent. (c) O₂ photoconsumption was always sensitive to O₂ concentration whatever the CO₂ concentration, but with O₂ exceeding 20% the kinetics disagreed with the Michaelis-Menten model, with saturation being reached more rapidly. With various CO₂ concentrations, the apparent K_m (O₂) ranged from 4 to 16% O₂ with a relatively constant V_max (O₂) of about one-third the V_max (CO₂). (d) Dark respiration seemed to be O₂ insensitive. These results are discussed in relation to the nature of the processes able to consume O₂ in the light, and seem to be consistent with a significant involvement of a Mehlertype reaction.     

Oxygen Uptake and Photosynthesis of the Red Macroalga, Chondrus crispus, in Seawater: Effects of Light and CO(2) Concentration

With an experimental system using mass spectrometry techniques and infra-red gas analysis of CO₂ developed for aquatic plants, we studied the responses to various light intensities and CO₂ concentrations of photosynthesis and O₂ uptake of the red macroalga Chondrus crispus S. The CO₂ exchange resistance at air-water interface which could limit the photosynthesis was experimentally measured. It allowed the calculation of the free dissolved CO₂ concentration. The response to light showed a small O₂ uptake (37% of net photosynthesis in standard conditions) compared to C₃ plants; it was always higher than dark respiration and probably included a photoindependent part. The response to CO₂ showed: (a) an O₂ uptake relatively insensitive to CO₂ concentration and not completely inhibited with high CO₂, (b) a general inhibition of gas exchanges below 130 microliters CO₂ per liter (gas phase), (c) an absence of an inverse relationship between O₂ and CO₂ uptakes, and (d) a low apparent K_m of photosynthesis for free CO₂ (1 micromolar). These results suggest that O₂ uptake in the light is the sum of different oxidation processes such as the glycolate pathway, the Mehler reaction, and mitochondrial respiration. The high affinity for CO₂ is discussed in relation to the use of HCO₃⁻ and/or the internal CO₂ accumulation.     

Heterogeneity of carrageenans from Chondrus crispus.

Carrageenans extracted from gametophytic and sporophytic Chondrus crispus were analysed by hydrolysis, KCl fractionation and 1H NMR spectroscopy. The carrageenan from gametophytic plants is composed predominantly of two KCl insoluble fractions which contain kappa-carrageenan as the major component with 1-carrageenan and sulphated galactans as minor components. The precursor mu- and v-carrageenans were not found in the soluble fraction. The extract from sporophytic plants is composed mainly of a KCl soluble fraction which could be separated into 10 fractions by ion-exchange chromatography. The major component did not show a lambda-type structure but one of a xi-carrageenan.     

The effect of Red Seaweed (Chondrus crispus) on the fertility of male albino rats

At different parts of the world, Red Seaweeds are one component of human diets especially at Southeast Asia. Red Seaweeds structurally contain bioactive molecules so; we studied the effect of Chondrus crispus on increasing the male albino rat fertility. Twelve male albino rats are used in this study as two group pre-treated group and post- treated one each with 6 animals. The pretreated group was dissected before the post-treated group injection. Each post treated rat injected intramuscular with 1 mg of Chondrus crispus with dose 0.1 ml/ twice per week for 48 day (Mukhtar et al., 2013).The results showed that increasing on the total testosterone levels insignificantly, sperm motility significantly, and decreasing in both FSH and DPPH levels insignificantly and significantly for the MDA levels in the post-treated group. The morphological appearance and histological examination for the sperm, testis and liver were normal as the pretreated group. The molecular studies showed absence of any DNA fragmentation for the testis of both group.The Red Seaweed has an enhanced effect in the testicular function of the animal which might increase their fertility and sexual activities.     

Ammonium uptake by Chondrus crispus Stackhouse (Gigartinales,Rhodophyta) in culture

Cultivated Chondrus crispus was used in N-NH₄ uptake experiments in the laboratory. An elevation of temperature increased the apparent rate of uptake, especially up to 11 °C. Uptake in the dark was found to be 83 % of that in the light. The apparent uptake decreased with increasing internal N pool; rates were 26.5, 22.2 and 20.2 µg N g dry wt^–1 min^–1 for internal N pools of 2.7, 3.5 and 4.6%, respectively. Apparent uptake increased with the substrate N concentration. The resulting curve has two components: an active uptake and a diffusion component at high (> 5000 µg N L^–1) external N levels. Ks and V _max were calculated by deducting the diffusion component from the uptake curve: these were of 497 µg N L ^–1 and 14.4 µg N g dry wt^–1 min^–1. respectively, and reflect a low substrate affinity. This could be the result of 10 years of continuous culture of C. crispus. Uptake was similarly followed in the culture tanks and showed comparable results; nighttime would be the most appropriate time to supply nutrients.     

Light-driven Uptake of Oxygen, Carbon Dioxide, and Bicarbonate by the Green Alga Scenedesmus

Mass spectrometric techniques were used to study several aspects of the competition between O₂ and species of inorganic carbon for photosynthetically generated reducing power in the green alga, Scenedesmus.     

Carrageenans in the gametophytic and sporophytic stages of Chondrus crispus

Summary The morphologically similar sporophytic and gametophytic plants of Chondrus crispus Stackhouse were examined and it was shown that the former contain -carrageenan. The gametophytes contain - and two additional carrageenans which are KCl-soluble and may comprise up to 25% of the total carrageenan. After alkaline modification, these KCl-soluble components were separated into a gel and a soluble carrageenan. The gel was indistinguishable from -carrageenan and presumably was derived from -carrageenan while the KCl-soluble fraction possessed a unique infrared spectrum easily distinguished from alkali-modified -carrageenan. This appears to represent a third carrageenan in the gametophytes.Our observations suggest that the biologically separate plants of C. crispus exhibit distinctive patterns of sulfation of their galactans. The sporophytes add SO₄ ^2- at C₂ of the precursor, whereas the gametophytes appear to add it principally at the available C₄ positions. Both types of plant are capable of sulfating at C₆ of the 4-linked galactose unit.Issued as NRC No. 13119.     

Protoplast production in Chondrus crispus gametophytes (gigartinales,rhodophyta)

Protoplasts were isolated from female gametophytes of Chondrus crispus (Stackh.) using commercial cellulase and various carrageenases prepared from marine bacteria. Depending on the nature of the donor tissue (apices or whole thallus, wild or cultivated strains), yields ranged from 1.0–8.5×10⁸ protoplasts per gram of fresh tissue. Preincubating the tissue with a potassium chelator, Kryptofix 222, enhanced protoplast yields by 30–50 %. Based on staining with fluorescein diacetate most protoplasts were viable. A few protoplasts regenerated a cell wall and divided.     

Characterization of the flavin association in hexose oxidase from Chondrus crispus

Hexose oxidase (EC 1.1.3.5) from Hansenula polymorpha was found to exhibit a dual covalent association of FAD with His79 via an 8 alpha-histidyl linkage as well as a covalent association between Cys138 and C-6 of the isoalloxazine moiety of FAD. Spectral properties of the wild-type enzyme exhibited maxima at 364 nm and 437 nm as well as a distinct shoulder at 445 nm. An H79K mutant enzyme exhibited only one maximum at 437 nm. The difference absorption spectrum between an oxidized and a substrate-reduced enzyme preparation showed maxima at 360 nm and 445 nm corresponding to an apparent novel type of association. Hexose oxidase showed a low, pH-independent fluorescence at 525 nm when excited at 450 nm. Flavin was released from the holoenzyme by treatment with trypsin. Sequencing of the flavopeptide revealed two peptides comprising positions 74-91 and 132-157 associated with FAD in equimolar amounts. A homology model of hexose oxidase was constructed using the crystal structure of glucooligosaccharide oxidase from Acremonium strictum as template. The model placed both of the sequences found above in the close vicinity of the FAD cofactor, and suggests covalent bonds between both His79 and Cys138 and FAD, in accordance with the chemical evidence. Based on the results, hexose oxidase is identified as incorporating FAD with a double covalent association with His79 and Cys138 in the holoenzyme. A reaction mechanism involving the concerted action of Tyr488 and Asp409 in hexose oxidase is suggested as the initiator of the proton abstraction from the substrate molecule in the active site.     

Etiology of infectious diseases in cultivated Chondrus crispus (Gigartinales,Rhodophyta)

The appearance of cavities and holes in fronds of commercially cultivated Chondrus crispus is described. These ultimately arise from the ravages of a green spot or green rot disease system in which several biotic agents can participate. Nematodes capable of bacterial grazing were recovered from necrotic lesions and we suggest that the nematodes can facilitate wound healing in diseased tissues. Bacteria isolated from disease lesions and from the surfaces of healthy fronds were screened for pathogenic strains. A particularly virulent one, the DOR isolate, was purified from small dark orange colored colonies grown on dilution plates. It was present in necrotic tissue and also recovered from surface scrapings of old healthy fronds, but not from their apical regions. Growth of the DOR isolate appeared to be inhibited by other bacteria colonizing the algal surface. It was shown to be a facultative pathogen, the virulence of which depended on the availability of ammonium or constituents easily metabolized to ammonium. It induced green rot disease in healthy C. crispus and was recoverable in pathogenic form from experimentally infected frond apices. A wound, disease and recovery cycle is discussed to illustrate potential interrelationships involving animal grazers, algal endophytes, Petersenia pollagaster, bacteria and nematodes.     

Drag, drafting, and mechanical interactions in canopies of the red alga Chondrus crispus.

Dense algal canopies, which are common in the lower intertidal and shallow subtidal along rocky coastlines, can alter flow-induced forces in their vicinity. Alteration of flow-induced forces on algal thalli may ameliorate risk of dislodgement and will affect important physiological processes, such as rates of photosynthesis. This study found that the force experienced by a thallus of the red alga Chondrus crispus (Stackhouse) at a given flow speed within a flow tank depended upon (1) the density of the canopy surrounding the thallus, (2) the position of the thallus within the canopy, and (3) the length of the stipe of the thallus relative to the height of the canopy. At all flow speeds, a solitary thallus experienced higher forces than a thallus with neighbors. A greater than 65% reduction in force occurred when the thallus drafted in the region of slower velocities that occurs in the wake region of even a single upstream neighbor, similar to the way racing bicyclists draft one behind the other. Mechanical interactions between thalli were important to forces experienced within canopies. A thallus on the upstream edge of a canopy experienced 6% less force than it did when solitary, because the canopy physically supported it. A thallus in the middle of a canopy experienced up to 83% less force than a solitary thallus, and forces decreased with increasing canopy density. Thus, a bushy morphology that increases drag on a solitary thallus may function to decrease forces experienced by that thallus when it is surrounded by a canopy, because that morphology increases physical support provided by neighbors.