Gérard Tremblin

Osmotic adjustment, gas exchanges and chlorophyll fluorescence of a hexaploid triticale and its parental species under salt stress

The effect of salt stress (NaCl 85.7 or 110 mmol/L) was investigated in the triticale T300 and its parental species, Triticum dicoccum farrum (Triticum df) and Secale cereale cv. Petkus. Triticum df and T300 were more salt-tolerant than the rye (110 mmol/L NaCl was the highest concentration allowing rye growth to the three-leaf stage). Na+, K+ and Cl- ions accounted for almost half of the osmotic adjustment in Triticum df and T300, and up to 90% in rye. Salinity decreased the net photosynthesis and transpiration rates of the three cereals as compared to control plants, but induced no significant change in chlorophyll a fluorescence parameters. Water-use efficiency (WUE) increased with salinity. In the presence of 110 mmol/L NaCl, the K+/Na+ ratio decreased markedly in rye as compared to the other two cereals. Proline concentration, which increased in Triticum df and T300, could have protected membrane selectivity in favour of K+. Proline content remained low in rye, and increasing soluble sugar content did not appear to prevent competition between Na+ and K+. The salt sensitivity of rye could be due to low K+ uptake in the presence of a high NaCl concentration.

Long-term photoacclimation of Haslea ostrearia (Bacillariophyta): effect of irradiance on growth rates, pigment content and photosynthesis

Haslea ostrearia, the peculiar diatom that develops in oyster-ponds and synthesizes a water-soluble blue pigment (marennine), was grown in a semi-continuous mode over a wide range of irradiances (20–750 μmol m−2 s−1). Growth, photosynthesis and pigment content were determined for algae maintained in exponential growth phase by regular dilution with fresh medium. Increasing the growth irradiance resulted in a decrease in the chloroplast length, but had no clear influence on the size of the cellular compartments pigmented by marennine accumulation. Growth rates increased with irradiance from 20 to 100 μmol m−1 s−1 and were constant from 100 to 750 μmol m−2 s−1. Increasing growth irradiance caused a decrease in the cellular content of chlorophylls a and c and fucoxanthin, in contrast to diadinoxanthin. Algae acclimated to high irradiance had lower maximum photosynthetic rate (P n m) and maximum light utilization coefficient (α) when expressed on a per cell basis. On a chlorophyll a basis, the higher the grow...

Suitability of the Fluorescence Monitoring System (FMS, Hansatech) for measurement of photosynthetic characteristics in algae

A pulse-modulated fluorescence measuring system, originally developed for higher plant studies, the Fluorescence Monitoring System (FMS; Hansatech), was tested to study photosynthesis in algae. The main technical features of the FMS are described, and applications of the saturating pulse fluorescence method are presented on micro- and macroalgae. Some limitations of the apparatus for measuring fluorescence characteristics of microalgae are discussed. Chlorophyll a fluorescence quenching analyses were performed on macroalgae from different taxonomic groups (Ulva sp., Palmaria palmata, Fucus serratus), and the results of the fluorescence measurements are presented and discussed, in relation to the macroalgae characteristics. The FMS and the saturating pulse method may be successfully used with green and red algae, in contrast to brown algae, with which F � m values higher than Fm were observed at low actinic light (<100mol m −2 s −1 ). This unconventional result is detected by error trapping routines and prevents employing the entire FMS potentiality. This point is discussed taking into account FMS specifications and limits.

Change in light quality due to a blue-green pigment, marennine, released in oyster-ponds: effect on growth and photosynthesis in two diatoms, Haslea ostrearia and Skeletonema costatum

Two prominent diatoms encountered in oyster-ponds,Haslea ostrearia and Skeletonema costatum,were grown in batch and in a semi-continuous modeunder light of different spectral quality, white, blueor blue-green. The last corresponded to white lightmodified by a water-soluble pigment, marennine,produced by H. ostrearia. After acclimation tothe different light treatments, the growth rates ofboth species showed little variation with respect tolight quality. The parameters for photosynthesisvs irradiance curves were very similar in H. ostrearia grown under the three light conditions,whereas S. costatum the maximum photosyntheticcapacity (on a chlorophyll a basis) wassignificantly reduced under blue-green light. Fluorescence analyses confirmed the data forphotosynthesis, with the operational fluorescenceyield decreasing faster with increasing irradiance inS. costatum grown under blue-green light. InH. ostrearia, fluorescence yields undersaturating irradiance were closely similar in thethree light conditions. The results are discussed inrelation with the prominent development of H.ostrearia that can outcompete other diatoms inoyster-ponds.

Enhancement of marennine production by blue light in the diatom Haslea ostrearia

The marine diatom Haslea ostrearia Simonsen produces a blue pigment, marennine, which is used for greening oysters. This microalga is cultured industrially indoors with artificial light. The influence of light quality on marennine production by cultures of H. ostrearia was investigated in the laboratory and at a semi-pilot scale (300 L tanks). In the first series of experiments in the laboratory, a clone of H. ostrearia was cultured under light of different colors (white, blue, green, yellow, and red) and at two irradiances (‘low’ and ‘high’, 20 and 100 μmol photons m−2 s−1, respectively). Compared to the white light controls, growth was increased in blue light at the ‘low’, but not at the ‘high’ irradiance, and marennine production at the end of the exponential phase was the highest in cells grown under blue light, regardless of the light quality or intensity during growth. Increased marennine production during growth was also observed, whichever color of light (blue or white) was used during the acclimation phase. In a second series of experiments, intraclonal differences were studied by comparing marennine production in seven clones differing with regard to their mean cell size. The total marennine expressed either per cell or per culture volume, was higher in blue light for all the clones. Complementary experiments carried out under semi-industrial conditions confirmed this effect of blue light, which could be relevant for the industrial, indoor production of marennine.

Zinc Affects Differently Growth, Photosynthesis, Antioxidant Enzyme Activities and Phytochelatin Synthase Expression of Four Marine Diatoms

Zinc-supplementation (20 μM) effects on growth, photosynthesis, antioxidant enzyme activities (superoxide dismutase, ascorbate peroxidase, catalase), and the expression of phytochelatin synthase gene were investigated in four marine diatoms (Amphora acutiuscula, Nitzschia palea, Amphora coffeaeformis and Entomoneis paludosa). Zn-supplementation reduced the maximum cell density. A linear relationship was found between the evolution of gross photosynthesis and total chlorophyll content. The Zn treatment decreased the electron transport rate except in A. coffeaeformis and in E. paludosa at high irradiance. A linear relationship was found between the efficiency of light to evolve oxygen and the size of the light-harvesting antenna. The external carbonic anhydrase activity was stimulated in Zn-supplemented E. paludosa but was not correlated with an increase of photosynthesis. The total activity of the antioxidant enzymes did not display any clear increase except in ascorbate peroxidase activity in N. palea. The phytochelatin synthase gene was identified in the four diatoms, but its expression was only revealed in N. palea, without a clear difference between control and Zn-supplemented cells. Among the four species, A. paludosa was the most sensitive and A. coffeaeformis, the most tolerant. A. acutiuscula seemed to be under metal starvation, whereas, to survive, only N. palea developed several stress responses.

IN-VIVO FLUORESCENCE MEASUREMENT OF PHOTOSYNTHESIS OF HASLEA OSTREARIA SIMONSEN IN RELATION TO MARENNINE CONTENT

Isolates of Haslea ostrearia containing different amounts of marennine have been investigated to elucidate the physiological role of this enigmatic blue pigment. Fluorescence analyses at room temperature and 77K showed that marennine is not involved in light-harvesting for either PS II or PS I. On the other hand, a light-shielding function of marennine was observed. With marennine present, the cells behaved similarly to organisms which are adapted to an unfavourable environment, i.e. conditions under which growth is hampered; as a result, the photosynthetic machinery needs protection from potential harmful light doses. Photosynthetic oxygen-evolution versus light intensity measurements supported the results of the fluorescence analysis, in that no lethal or sublethal damage of marennine-containing cells was observable after treatment with strong light The importance of such an unusual pigment that shields red-light is discussed for organisms such as diatoms and brown algae that contain light-harvesting ca...

Cadmium, Copper, Sodium and Zinc Effects on Diatoms: from Heaven to Hell — a Review

Abstract Diatom development depends on several environmental factors, including the availability in metals. When micronutrients are present of adequate amount, cells exhibit a strong fitness and develop at their maximum growth rate. In many circumstances, the optimal metal amount in the cell environment is disrupted and cells experience starvation or excess for one or more elements. The metals in excess interfere with biochemical and cellular processes triggering a dysfunctioning that reduces growth and may ultimately lead to cell death. The ability of diatoms to adapt/resist to environmental changes has ecological consequences in term of biodiversity. To survive, diatoms activate defence mechanisms, such as the production of antioxidants or/and metal chelators. In this contribution, the diatom requirements for cadmium, copper, zinc and sodium are briefly reviewed. Then the impacts of an excess or a deprivation in one of these elements on diatom physiology is discussed from the molecular and biochemical point of views. The defence mechanisms enabling diatoms to overcome the metal stress are presented. At the end of this contribution, an assay on the integration of the defence mechanisms is presented.

The role of Odontella aurita , a marine diatom rich in EPA, as a dietary supplement in dyslipidemia, platelet function and oxidative stress in high-fat fed rats

BackgroundDietary changes are a major factor in determining cardiovascular risk. n-3 polyunsaturated fatty acids modulate the risk factors for metabolic syndrome via multiple mechanisms, including the regulation of the lipid metabolism. We therefore investigated the effect of Odontella aurita, a microalga rich in EPA, which is already used as a food supplement, on the risk factors for high-fat diet induced metabolic syndrome in rats.MethodsMale Wistar rats were divided into 4 groups and were fed with a standard diet (control); with the standard diet supplemented with 3% freeze-dried O. aurita (COA); with a high-fat diet (HF); or with the high-fat diet supplemented with 3% of freeze-dried O. aurita (HFOA) for 7 weeks. In this study we evaluated the impact of these different diets on the risk factors for metabolic syndrome, such as hyperlipidemia, platelet aggregation, thromboxane B2 production, and oxidative stress.ResultsAfter 7 weeks of treatment, high fat feeding had increased final body weight, glycemia, triacylglycerol, and total cholesterol levels in plasma and liver compared to the control diet. Collagen-induced platelet aggregation and basal platelet thromboxane B2 were also higher in the high-fat fed rats than in those in the control group. In the liver, oxidative stress was greater in the HF group than in the control group. O. aurita intake in HFOA-fed rats resulted in lower glycemia and lipid levels in the plasma and liver relative than in the HF group. Thus, in the HFOA group, n-3 polyunsaturated fatty acid levels in the tissues studied (plasma, liver, and platelets) were higher than in the HF group. Platelet hyper-aggregability tended to decrease in HFOA-fed rats as basal platelet thromboxane B2 production decreased. Finally, O. aurita reduced oxidative stress in the liver, with lower malondialdehyde levels and increased glutathione peroxidase activity.ConclusionsO. aurita is a marine diatom rich in EPA as well as in other bioactive molecules, such as pigments. The synergistic effect of these microalgal compounds, displayed a beneficial effect in reducing the risk factors for high-fat induced metabolic syndrome: hyperlipidemia, platelet aggregation, and oxidative stress.

ENVIRONMENTAL FACTORS AFFECTING GROWTH AND OMEGA 3 FATTY ACID COMPOSITION INSKELETONEMA COSTATUM.THE INFLUENCES OF IRRADIANCE AND CARBON SOURCE: Communication presented at the 25èmeCongrès Annuel de l'Association des Diatomistes de Langue Francaise (ADLaF), Caen, 25-28 September 2006

The effects of carbon sources and three different irradiance levels on the growth and polyunsaturated fatty acid composition of the diatom Skeletonema costatum have been studied. Diatoms were grown in artificial seawater (ASW), which contained sodium bicarbonate (photoautotrophic growth) or sodium acetate (photoheterotrophic growth) at the same concentration (2.07 mM). The optimum growth conditions were between 100–340 μmol photons m−2 s−1 in presence of sodium bicarbonate, both of which enhance photosynthesis. However, under limiting irradiance, results suggested that sodium acetate was more efficiently used than sodium bicarbonate during batch growth. As a consequence, in natural conditions and under low irradiance, availability of sodium acetate could be a limiting factor for cell metabolism. This diatom also seems to be able to support efficiently mixotrophic growth under low irradiance (20 μmol photons m−2 s−1). The highest eicosapentaenoic acid (EPA) amounts were observed when cells were cultured under saturating irradiance (340 μmol photons m−2 s−1) during the late experimental and stationary phases. On the contrary, an increase in the EPA level was observed during the decline phase under limiting irradiance. Indeed, at low irradiance, an accumulation of omega 3 fatty acids in the thylakoid membranes could facilitate the photosynthetic reactions suggesting a peculiar photoadaptation of Skeletonema costatum. Finally, during the exponential phase, a decreased of omega 3 fatty acid amount and specifically EPA with acetate as a carbon source has been observed under limiting and saturating irradiance. This could be explained by the decreased acetate availability that could be considered as responsible for the fall in EPA level.The effects of carbon sources and three different irradiance levels on the growth and polyunsaturated fatty acid composition of the diatom Skeletonema costatum have been studied. Diatoms were grown in artificial seawater (ASW), which contained sodium bicarbonate (photoautotrophic growth) or sodium acetate (photoheterotrophic growth) at the same concentration (2.07 mM). The optimum growth conditions were between 100–340 μmol photons m−2 s−1 in presence of sodium bicarbonate, both of which enhance photosynthesis. However, under limiting irradiance, results suggested that sodium acetate was more efficiently used than sodium bicarbonate during batch growth. As a consequence, in natural conditions and under low irradiance, availability of sodium acetate could be a limiting factor for cell metabolism. This diatom also seems to be able to support efficiently mixotrophic growth under low irradiance (20 μmol photons m−2 s−1). The highest eicosapentaenoic acid (EPA) amounts were observed when cells were cultured un...