Effects of sodium bicarbonate concentration on growth, photosynthesis, and carbonic anhydrase activity of macroalgae Gracilariopsis lemaneiformis, Gracilaria vermiculophylla, and Gracilaria chouae (Gracilariales, Rhodophyta).

There is potential for bicarbonate to improve crop yields and economic efficiency of marine algae. However, few studies have focused on the effect of bicarbonate on the growth, photosynthesis, and enzyme activity associated with carbon utilization, especially in commercial macroalgae. Here, the addition of bicarbonate (up to 420 mg L(-1)) to macroalgal cultures has been evaluated for Gracilariopsis lemaneiformis, Gracilaria vermiculophylla, and Gracilaria chouae with respect to growth rate, photosynthetic activity, carbonic anhydrase activity, and biochemical composition. The results showed that the effects of NaHCO3 on growth, chlorophyll a, phycoerythrin, photosynthetic oxygen evolution, photochemical parameters of PSI and PSII, carbonic anhydrase activity, and nitrogen content were significant (P < 0.05) and followed the same pattern in the three species. The parameter values were promoted in lower NaHCO3 concentrations (up to 252 or 336 mg L(-1)) and inhibited in higher NaHCO3 concentrations (>336 mg L(-1) for Gp. lemaneiformis and >420 mg L(-1) for the other two species). Moreover, species-specific differences induced by supplementation with bicarbonate were discovered during culture. Optimal concentrations of NaHCO3 used in this study were 252 mg L(-1) for Gp. lemaneiformis and 336 mg L(-1) for G. vermiculophylla and G. chouae. These results suggest that an adequate supplementation of sodium bicarbonate is a viable strategy for promoting growth and photosynthetic activity in some macroalgae as well as for improving biochemical composition. The study will help to accelerate the growth rate of algae and improve the quality of thalli, and will also be useful for enhancing the understanding of carbon utilization in macroalgae.

Methyl Jasmonate-Induced Lipidomic and Biochemical Alterations in the Intertidal Macroalga Gracilaria dura (Gracilariaceae, Rhodophyta).

The role of exogenously added methyl jasmonate (MeJA), a lipid-derived signaling compound, in inducing oxidative stress in the marine red macroalga Gracilaria dura was investigated. MeJA at a concentration of 1-100 µM was a strong stimulant of reactive oxygen species (H(2)O(2), HO· and O(2) (·-)) (P < 0.05) causing considerable oxidative stress in G. dura. This further led to lipid peroxidation and degradation of the pigments Chl a and phycocyanin, with a concomitant increase in phycoerythrin. The MeJA-induced oxidative burst also led to the induction of a fatty acid oxidation cascade, resulting in the synthesis of hydroxy-oxylipins and the up-regulation of the 13-lipoxygenase pathway. Electrospray ionization-mass spectrometry-based shotgun lipidomic analysis revealed that monogalactosyldiacylglycerol (a chloroplastic glycerolipid) and phosphatidylcholine (extrachloroplastidic phopholipid) were the most affected lipid classes. The degradation of 18:3-fatty acid-containing monogalactosyldiacylglycerol inferred that it provided fatty acyl chains for the biosynthesis of 13-hydroperoxylinolenic acid, which was further directed towards either the jasmonate pathway or other alternative pathways of the fatty acid oxidation cascade, analogous to higher plants. Also, G. dura modulated the lipid acyl chains in such a way that no significant change was observed in the fatty acid profile of the treated thalli as compared with those of the control, except for C16:0, C16:1 (n-9), C20:3 (n-6) and C20:4 (n-6) (P < 0.05). Furthermore, MeJA caused the accumulation of phenolic compounds and the up-regulation of enzymes involved in secondary metabolism such as polyphenol oxidase, shikimate dehydrogenase and phenylalanine ammonia-lyase, indicating a shift towards secondary metabolism as a defense strategy to combat the induced oxidative stress.

The effects of lead and copper on the cellular architecture and metabolism of the red alga Gracilaria domingensis.

The effect of lead and copper on apical segments of Gracilaria domingensis was examined. Over a period of 7 days, the segments were cultivated with concentrations of 5 and 10 ppm under laboratory conditions. The samples were processed for light, confocal, and electron microscopy, as well as histochemistry, to evaluate growth rates, mitochondrial activity, protein levels, chlorophyll a, phycobiliproteins, and carotenoids. After 7 days of exposure to lead and copper, growth rates were slower than control, and biomass loss was observed on copper-treated plants. Ultrastructural damage was primarily observed in the internal organization of chloroplasts and cell wall thickness. X-ray microanalysis detected lead in the cell wall, while copper was detected in both the cytoplasm and cell wall. Moreover, lead and copper exposure led to photodamage of photosynthetic pigments and, consequently, changes in photosynthesis. However, protein content and glutathione reductase activity decreased only in the copper treatments. In both treatments, decreased mitochondrial NADH dehydrogenase activity was observed. Taken together, the present study demonstrates that (1) heavy metals such as lead and copper negatively affect various morphological, physiological, and biochemical processes in G. domingensis and (2) copper is more toxic than lead in G. domingensis.

Toxicity and Mechanisms of Action of Polycyclic Aromatic Hydrocarbon Pollution in Red Algae (Gracilaria corticata) from the Northern Coast of the Oman Sea.

The activities of selected biomarkers including 7-ethoxycoumarin-O-deethylase (ECOD) and glutathione S-transferase (GST) were measured in the red algae (Gracilaria corticata) obtained from the Oman Sea. Chemical analyses were used to assess the polycyclic aromatic hydrocarbons (PAHs) in the red algae. Total PAH concentrations in the red algae ranged from 3.61 to 8.14 ng g-1 dry weight. Mean GST and ECOD activity also varied from 8.87 to 15.32 nmol/mg protein/min and from 0.31 to 1.02 pmol/min/mg protein, respectively. Significant correlations were found between the total PAH levels and the selected biomarkers (p < 0.01). The results showed that ECOD and GST enzymes reacted to PAHs in phase I and II detoxification mechanisms of red algae (G. corticata), which extend the use of these biomarkers for investigation of the biological effects of PAH pollution as well as determination of pollution bioavailability. Environ Toxicol Chem 2019;38:1947-1953. © 2019 SETAC.

Proteome responses of Gracilaria lemaneiformis exposed to lead stress.

Proteome response of plants is an important process that enables them to cope with environmental stress including metal stress. In this study, the proteome of Gracilaria lemaneiformis exposed to lead was investigated. Two-dimensional gel electrophoresis analysis revealed 123 protein spots, among which 14 proteins were significantly differentially expressed and identified using MALDI-TOF MS. Two of the up-regulated proteins were identified and predicted to be involved in photosynthesis and signal transduction, while eleven down-regulated proteins were functionally grouped into five classes including photosynthesis, energy metabolism, protein metabolism, carbohydrate transport and metabolism, and antioxidation proteins. There was also an up-regulation in superoxide dismutase, peroxidase, glutathione s-transferase, and heat-shock protein 70 upon Pb exposure. Proteomic studies provide a better picture of protein networks and metabolic pathways primarily involved in intracellular detoxification and defense mechanisms.

Toxic effect of nonylphenol on the marine macroalgae Gracilaria lemaneiformis (Gracilariales, Rhodophyta): antioxidant system and antitumor activity.

The objective of the present work was to evaluate the toxic effect of nonylphenol (NP) on the antioxidant response and antitumor activity of Gracilaria lemaneiformis. An obvious oxidative damage was observed in this study. The thallus exposed to NP showed 1.2-2.0-fold increase in lipid peroxide and displayed a maximum level of 16.58 µmol g-1 Fw on 0.6 mg L-1 for 15-day exposure. The activities of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) enhanced significantly by 1.1-3.2-fold and subsequently diminished at the high concentrations and prolonged exposure. The results of DNA damage in comet assay also supported that NP was obviously toxic on G. lemaneiformis with increasing the percentage of tail DNA in a dose-dependent manner. Furthermore, the ethanol extract of G. lemaneiformis (EEGL) did exhibit antitumor potential against HepG-2 cells. While decreased in cell inhibition, ROS generation, apoptosis, and caspase-3 in HepG-2 cells treated with the EEGL were observed when G. lemaneiformis was exposed to NP for 15 days, and which were related to exposure concentration of NP. These suggested that NP has strongly toxic effect on the antitumor activity of G. lemaneiformis. The results revealed in this study imply that macroalgae can be useful biomarkers to evaluate marine pollutions.

Toxic effect of metal cation binary mixtures to the seaweed Gracilaria domingensis (Gracilariales, Rhodophyta).

The macroalga Gracilaria domingensis is an important resource for the food, pharmaceutical, cosmetic, and biotechnology industries. G. domingensis is at a part of the food web foundation, providing nutrients and microelements to upper levels. As seaweed storage metals in the vacuoles, they are considered the main vectors to magnify these toxic elements. This work describes the evaluation of the toxicity of binary mixtures of available metal cations based on the growth rates of G. domingensis over a 48-h exposure. The interactive effects of each binary mixture were determined using a toxic unit (TU) concept that was the sum of the relative contribution of each toxicant and calculated using the ratio between the toxicant concentration and its endpoint. Mixtures of Cd(II)/Cu(II) and Zn(II)/Ca(II) demonstrated to be additive; Cu(II)/Zn(II), Cu(II)/Mg(II), Cu(II)/Ca(II), Zn(II)/Mg(II), and Ca(II)/Mg(II) mixtures were synergistic, and all interactions studied with Cd(II) were antagonistic. Hypotheses that explain the toxicity of binary mixtures at the molecular level are also suggested. These results represent the first effort to characterize the combined effect of available metal cations, based on the TU concept on seaweed in a total controlled medium. The results presented here are invaluable to the understanding of seaweed metal cation toxicity in the marine environment, the mechanism of toxicity action and how the tolerance of the organism.

Sequential acid and enzymatic hydrolysis in situ and bioethanol production from Gracilaria biomass.

Gracilaria sp., a red alga, was used as a feedstock for the production of bioethanol. Saccharification of Gracilaria sp. by sequential acid and enzyme hydrolysis in situ produced a high quality hydrolysate that ensured its fermentability to produce ethanol. The optimal saccharification process resulted in total 11.85g/L (59.26%) of glucose and galactose, Saccharomyces cerevisiae Wu-Y2 showed a good performance on co-fermentability of glucose and galactose released in the hydrolysate from Gracilaria sp. The final ethanol concentrations of 4.72g/L (0.48g/g sugar consumed; 94% conversion efficiency) and the ethanol productivity 4.93g/L/d were achieved. 1g of dry Gracilaria can be converted to 0.236g (23.6%) of bioethanol via the processes developed. Efficient alcohol production by immobilized S. cerevisiae Wu-Y2 in batch and repeated batch fermentation was also demonstrated. The findings of this study revealed that Gracilaria sp. can be a potential feedstock in biorefinery for ethanol production.

Prediction of mono-, bi-, and trivalent metal cation relative toxicity to the seaweed Gracilaria domingensis (Gracilariales, Rhodophyta) in synthetic seawater.

The present study reports a 48-h aquatic metal-toxicity assay based on daily growth rates of the red seaweed Gracilaria domingensis (Gracilariales, Rhodophyta) in synthetic seawater. The median inhibitory concentration (IC50) for each metal cation was experimentally determined, and the ratios of free ions (aqueous complex) were calculated by software minimization of the total equilibrium activity (MINTEQA2) to determine the free median inhibitory concentration (IC50F). A model for predicting the toxicity of 14 metal cations was developed using the generic function approximation algorithm (GFA) with log IC50F values as the dependent variables and the following properties as independent variables: ionic radius (r), atomic number (AN), electronegativity (Xm ), covalent index (Xm (2) r), first hydrolysis constant (|log KOH |), softness index (σp ), ion charge (Z), ionization potential (ΔIP), electrochemical potential (ΔEo ), atomic number divided by ionization potential (AN/ΔIP), and the cation polarizing power for Z(2) /r and Z/AR. The 3-term independent variables were predicted as the best-fit model (log IC50F: -23.64 + 5.59 Z/AR + 0.99 |log KOH | + 37.05 σp ; adjusted r(2) : 0.88; predicted r(2) : 0.68; Friedman lack-of-fit score: 1.6). This mathematical expression can be used to predict metal-biomolecule interactions, as well as the toxicity of mono-, bi-, and trivalent metal cations, which have not been experimentally tested in seaweed to date. Quantitative ion-character relationships allowed the authors to infer that the mechanism of toxicity might involve an interaction between metals and functional groups of biological species containing sulfur or oxygen.

Changes in ultrastructure and cytochemistry of the agarophyte Gracilaria domingensis (Rhodophyta, Gracilariales) treated with cadmium.

The agarophyte macroalgae Gracilaria domingensis (Kützing) Sonder ex Dickie is widely distributed along the Brazilian coast. While this species produces agarana, it is more important in the human diet. Therefore, the present study aimed to evaluate the biological effects of cadmium on its morphology and cellular organization. To accomplish this, the effects of cadmium in apical segments of G. domingensis were examined in vitro. Over a period of 16 days, the segments were cultivated and exposed to photosynthetically active radiation (PAR) at 80 µmol photons m(-2) s(-1), with cadmium treatments in doses of 100, 200 and 300 µM. The samples were processed for light, transmission and scanning electron microscopy. Histochemical analyses included Toluidine Blue for acidic polysaccharides, Coomassie Brilliant Blue for total protein, and Periodic Acidic Schiff for neutral polysaccharides. In all cadmium treatments, cytochemical analysis showed 1) metachromatic granulation in vacuole and lenticular thickness of the cell wall, 2) a higher concentration of cytoplasmic organelles, and 3) an increase in the number of floridean starch grains. Cadmium also caused changes in the ultrastructure of cortical and subcortical cells, including increased cell wall thickness and vacuole volume, as well as the destruction of chloroplast internal organization and increased number of plastoglobuli. In addition, treated plants showed a gradual increase in surface roughness, apparently the result of cadmium absorption. Taken together, these findings strongly suggested that cadmium negatively affects the agarophyte G. domingensis, posing a threat to the vitality of this plant species as a supplement in the human diet.

NH4+ enrichment and UV radiation interact to affect the photosynthesis and nitrogen uptake of Gracilaria lemaneiformis (Rhodophyta).

Solar ultraviolet radiation (UVR, 280-400 nm) is known to inhibit the photosynthesis of macroalgae, whereas nitrogen availability may alter the sensitivity of the algae to UVR. Here, we show that UV-B (280-315 nm) significantly reduced the net photosynthetic rate of Gracilaria lemaneiformis. This inhibition was alleviated by enrichment with ammonia, which also caused a decrease in dark respiration. The presence of both UV-A (315-400 nm) and UV-B stimulated the accumulation of UV-absorbing compounds. However, this stimulation was not affected by enrichment with ammonia. The content of phycoerythrin (PE) was increased by the enrichment of ammonia only in the absence of UVR. Ammonia uptake and the activity of nitrate reductase were repressed by UVR. However, exposure to UVR had an insignificant effect on the rate of nitrate uptake. In conclusion, increased PE content associated with ammonia enrichment played a protective role against UVR in this alga, and UVR differentially affected the uptake of nitrate and ammonia.

Selenium and spermine alleviate cadmium induced toxicity in the red seaweed Gracilaria dura by regulating antioxidants and DNA methylation.

The protective role of exogenously supplied selenium (Se) and polyamines (PAs) such as putrescine (Put) and spermine (Spm) in detoxifying the cadmium (Cd) induced toxicity was studied in the marine red alga Gracilaria dura in laboratory conditions. The Cd exposure (0.4 mM) impede the growth of alga while triggering the reactive oxygen species (ROS viz. O(2)(•-) and H(2)O(2)) generation, inhibition of antioxidant system, and enhancing the lipoxygenase (LOX) activity, malondialdehyde (MDA) level and demethylation of DNA. Additions of Se (50 µM) and/or Spm (1 mM) to the culture medium in contrast to Put, efficiently ameliorated the Cd toxicity by decreasing the accumulation of ROS and MDA contents, while restoring or enhancing the level of enzymatic and nonenzymatic antioxidants and their redox ratio, phycobiliproteins and phytochelatins, over the controls. The isoforms of antioxidant enzymes namely superoxide dismutase (Mn-SOD, ~150 kDa; Fe-SOD ~120 kDa), glutathione peroxidase (GSH-Px, ~120 and 140 kDa), glutathione reductase (GR, ~110 kDa) regulated differentially to Se and/or Spm supplementation. Furthermore, it has also resulted in enhanced levels of endogenous PAs (specially free and bound insoluble Put and Spm) and n-6 PUFAs (C20-3, n-6 and C20-4, n-6). This is for the first time wherein Se and Spm were found to regulate the stabilization of DNA methylation by reducing the events of cytosine demethylation in a mechanism to alleviate the Cd stress in marine alga. The present findings reveal that both Se and Spm play a crucial role in controlling the Cd induced oxidative stress in G. dura.

[Physiological responses of Gracilaria lemaneiformis to copper stress].

Gracilaria lemaneiformis was exposed to 0, 25, 50, 100, 250 and 500 microg x L(-1) of Cu2+ to study its physiological responses to Cu2+ stress. When the Cu2+ concentration was > or = 50 microg x L(-1), the relative growth rate (RGR) of G. lemaneiformis decreased significantly, and the optimal quantum yield (Fv/Fm), the maximum relative electron transfer rate (rETRmax), and the relative electron transfer efficiency (alpha) exhibited the same variation trend, compared with the control. With the increase of Cu2+ concentration, the maximum net photosynthetic rate (Pmax) and light saturation point (LSP) decreased significantly, light compensation point (LCP) had a significant increase, while chlorophyll a, carotenoid, and phycobiliprotein contents decreased after an initial increase. When the Cu2+ concentration reached 500 microg x L(-1), the chlorophyll a, carotenoid, and phycobiliprotein contents decreased significantly. It was suggested that G. lemaneiformis could tolerate low concentration Cu2+ stress, but its physiological activities were inhibited markedly when exposed to > or =50 microg x L(-1) of Cu2+.