Chemical characterisation and analysis of the cell wall polysaccharides of duckweed (Lemna minor)

An Ionic Liquid-Based Biorefinery Approach for Duckweed Utilization

This study establishes a foundation for the ionic liquid (IL) pretreatment of duckweed biomass. An optimized IL-based process was designed to exploit the unique properties of duckweed including efficient metal removal, potential starch accumulation, and protein accumulation. Two ILs, namely, dimethylethanolammonium formate ([DMEtA][HCOO]) and N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), were investigated for the pretreatment of two duckweed species (Spirodela polyrhiza and Lemna minor). The evaluation focused on starch recovery, sugar release, protein recovery, and metal extraction capabilities. [DMEtA][HCOO] demonstrated near-quantitative starch recoveries at 120 °C, while [DMBA][HSO4] showed similar performance at 90 °C within a reaction time of 2 h. Saccharification yields for most pulps exceeded 90% after 8 h of hydrolysis, outperforming "traditional" lignocellulosic biomasses such as miscanthus or sugarcane bagasse. Approximately 50 and 80 wt % of the protein were solubilized in [DMEtA][HCOO] and [DMBA][HSO4], respectively, while the remaining protein distributed between the pulp and lignin. However, the solubilized protein in the IL could not be recovered due to its low molecular weight. Regarding metal extraction, [DMEtA][HCOO] demonstrated higher efficiency, achieving 81% removal of Ni from Lemna minor's pulps, whereas [DMBA][HSO4] extracted only 28% of Ni with slightly higher pulp concentrations. These findings indicate the need for further optimization in concurrent metal extraction using ILs.

Cellulose Nanocrystals and Lignin Nanoparticles Extraction from Lemna minor L.: Acid Hydrolysis of Bleached and Ionic Liquid-Treated Biomass

Using biomass to develop and obtain environmentally friendly and industrially applicable biomaterials is increasingly attracting global interest. Herein, cellulose nanocrystals (CNCs) and lignin nanoparticles (LNPs) were extracted from Lemna minor L., a freshwater free-floating aquatic species commonly called duckweed. To obtain CNCs and LNPs, two different procedures and biomass treatment processes based on bleaching or on the use of an ionic liquid composed of triethylammonium and sulfuric acid ([TEA][HSO4]), followed by acid hydrolysis, were carried out. Then, the effects of these treatments in terms of the thermal, morphological, and chemical properties of the CNCs and LNPs were assessed. The resulting nanostructured materials were characterized by using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, thermo-gravimetric analysis (TGA), and scanning electron microscopy (SEM). The results showed that the two methodologies applied resulted in both CNCs and LNPs. However, the bleaching-based treatment produced CNCs with a rod-like shape, length of 100-300 nm and width in the range of 10-30 nm, and higher purity than those obtained with ILs that were spherical in shape. In contrast, regarding lignin, IL made it possible to obtain spherical nanoparticles, as in the case of the other treatment, but they were characterized by higher purity and thermal stability. In conclusion, this research highlights the possibility of obtaining nanostructured biopolymers from an invasive aquatic species that is largely available in nature and how it is possible, by modifying experimental procedures, to obtain nanomaterials with different morphological, purity, and thermal resistance characteristics.

Characterization of Bioactive Metabolites and Antioxidant Activities in Solid and Liquid Fractions of Fresh Duckweed (Wolffia globosa) Subjected to Different Cell Wall Rupture Methods

Fresh Wolffia globosa, the smallest flowering plant well-known for its favorable nutrient composition and rich content of bioactive compounds, was subjected to boiling, freeze-thawing, and mechanical crushing to reduce its excessive (95-96%) moisture level and consequent drying time. The resultant three wolffia matrixes were filtered through a plankton net to fractionate into the residue and the filtrate. The proximate composition, bioactive metabolites, antioxidant activity, and characterization of bioactive metabolites by LC-ESI-QTOF-MS/MS and Fourier transform infrared spectroscopy were made from oven-dried residues and filtrates. Among residues, crude protein (29.84%), crude lipid (5.77%), total carotenoids (TCC; 722.8 μg/g), and vitamin C (70.02 mg/100 g) were the highest (p < 0.05) for freeze-thawing against higher ash (7.99%), total phenolic content (TPC; 191.47 mg GAE g-1 dry weight), total flavonoid content (TFC; 91.54 mg QE g-1 dry weight), DPPH activity (47.46%), and ferric reducing antioxidant power (FRAP) activity (570.19 μmol FeSO4 equiv/mg) for the crushed counterpart and Chl-b in residues from boiling. No significant variation was evident in the total tannin content (TTC). Among filtrates, higher total phenolic content (773.29 mg GAE g-1 dry weight), TFC (392.77 mg QE g-1 dry weight), TTC (22.51 mg TAE g-1), and antioxidant activity as DPPH activity (66.46%) and FRAP (891.62 μmol FeSO4 equiv/mg) were evident for boiling, while that from crushing exhibited the highest TCC (1997.38 μg/g DM). LC-ESI-QTOF-MS/MS analysis identified 72 phenolic compounds with the maximum in residue (33) and filtrate (33) from freeze-thawing, followed by crushing (18 and 19) and boiling (14 and 13) in order, respectively. The results indicated that the predrying cell rupturing method significantly impacted quantitative, as well as qualitative compositions of residues and filtrates from fresh wolffia.

Duckweed pectic-arabinogalactan-proteins can crosslink through borate diester bonds

Material containing pectin and arabinogalactan-protein (AGP) was released and purified from Spirodela alcohol insoluble residues. Results of carbohydrate analyses and two-dimensional NMR spectroscopy suggest that this material is composed of apiogalacturonan and rhamnogalacturonan-I covalently attached to AGPs. 11B NMR spectroscopy indicated that some of the glycoses in this complex exist as their boric acid monoesters. Borate diesters were formed when the pectic-AGPs were allowed to react at pH above 6.2 with the boron-depleted pectic-AGPs, suggesting that in vitro two pectic-AGP molecules can crosslink to one another through borate. Borate diesters also formed when the pectic-AGPs were incubated with monomeric rhamnogalacturonan-II in the presence of Pb2+ ion at pH 9.2. This data presents evidence of the first wall polymer after rhamnogalacturonan-II to crosslink through borate diesters. We suggest that the formation of these borate-crosslinks may help Spirodela respond to high-pH condition.

Structural characterization of cell-wall polysaccharides purified from chayote (Sechium edule) fruit

Chayote (Sechium edule), an underutilized cucurbit vegetable crop, has gained attention as it exhibits health-promoting properties. However, the primary structure of chayote cell-wall polysaccharides has not been comprehensively studied. In this study, two cell-wall polysaccharides, CP-1 (41.1 KDa) and CP-2 (15.6 KDa), were extracted from chayote, and the structural analysis of CP-1 and CP-2 was carried out by monosaccharide composition analysis, Fourier transform infrared spectroscopy (FTIR), methylation analysis, and nuclear magnetic resonance spectroscopy (NMR). The results demonstrated that CP-1 was a galactan, and CP-2 was an anionic heteropolysaccharide composed of galacturonic acid, galactose, arabinose, rhamnose, glucose, glucuronic acid, mannose, and xylose in the molar ratio of 31.2:26.3:24.9:7.4:6.5:1.9:1.3:0.5. CP-2 has a backbone of → 4)-β-d-Galp-(1 → 3,6)-β-d-Galp-(1 → 3)-β-d-Galp-(1 → 4)-α-d-GalpA-(1→, with branches at O-6 of → 3,6)-β-d-Galp-(1→, consisting of α-l-Araf-(1 → 5)-α-l-Araf-(1 → 4)-β-d-Glcp-(1 →. Analysis of the structural and physicochemical properties confirmed the excellent application characteristics of CP-1 and CP-2. Hence, cell-wall polysaccharides of chayote could be used as new polysaccharides materials.

Seasonal Variation in Cell Wall Composition and Carbohydrate Metabolism in the Seagrass Posidonia oceanica Growing at Different Depths

Posidonia oceanica is a common seagrass in the Mediterranean Sea that is able to sequester large amounts of carbon. The carbon assimilated during photosynthesis can be partitioned into non-structural sugars and cell-wall polymers. In this study, we investigated the distribution of carbon in starch, soluble carbohydrates and cell-wall polymers in leaves and rhizomes of P. oceanica. Analyses were performed during summer and winter in meadows located south of the Frioul archipelago near Marseille, France. The leaves and rhizomes were isolated from plants collected in shallow (2 m) and deep water (26 m). Our results showed that P. oceanica stores more carbon as starch, sucrose and cellulose in summer and that this is more pronounced in rhizomes from deep-water plants. In winter, the reduction in photoassimilates was correlated with a lower cellulose content, compensated with a greater lignin content, except in rhizomes from deep-water plants. The syringyl-to-guaiacyl (S/G) ratio in the lignin was higher in leaves than in rhizomes and decreased in rhizomes in winter, indicating a change in the distribution or structure of the lignin. These combined data show that deep-water plants store more carbon during summer, while in winter the shallow- and deep-water plants displayed a different cell wall composition reflecting their environment.

Phytoremediation of toxic chemicals in aquatic environment with special emphasis on duckweed mediated approaches

The discharge of toxic chemicals into water bodies and their linked detrimental effects on health is a global concern. Phytoremediation, an environment-friendly plant-based technology, has gained intensive interest over the last decades. For the aquatic phytoremediation process, the commonly available duckweeds have recently attracted significant attention due to their capacity to grow in diverse ecological niches, fast growth characteristics, suitable morphology for easy handling of biomass, and capacity to remove and detoxify various potential toxic elements and compounds. This review presents the progress of duckweed-assisted aquatic phytoremediation of toxic chemicals. A brief background of general phytoremediation processes, including the different phytoremediation methods and advances in understanding their underlying mechanisms, has been described. A summary of different approaches commonly practiced to assess the growth of the plants and their metal removal capacity in the phytoremediation process has also been included. A vast majority of studies have established that duckweed is an efficient plant catalyst to accumulate toxic heavy metals and organic contaminants, such as pesticides, fluorides, toxins, and aromatic compounds, reducing their toxicity from water bodies. The potential of this plant-based phytoremediation process for its downstream applications in generating value-added products for the rural economy and industrial interest has been identified.

Biogas Potential Assessment of the Composite Mixture from Duckweed Biomass

The article presents the research results of anaerobic digestion processes in bioreactors of composite mixtures based on initial and residual biomass of Lemna minor duckweed and additives: inoculum (manure), food waste, and spent sorbents to determine biogas potential (biogas volume, methane content). Duckweed Lemna minor, which is widespread in freshwater reservoirs, is one of the promising aquatic vegetation species for energy use. Residual biomass is obtained by chemically extracting valuable components from the primary product. The purpose of the research was to evaluate the possibility of the energy potential of residual biomass of Lemna minor to reduce the consumption of fossil fuels and reduce greenhouse gas emissions. This is in line with the International Energy Agency (IEA) scenarios for the reduction of environmental impact. The obtained results confirm the feasibility of using this type of waste for biogas/biomethane production. The recommendations on the optimal composition of the mixture based on the residual biomass of Lemna minor, which will allow for an increase in biogas production, are given. The obtained data can be used in the design of bioreactors.

Progress in thermochemical conversion of duckweed and upgrading of the bio-oil: A critical review

The processing of duckweed has been included in the list of promising pathways for biofuels production. This property is attributed to its simple manual harvesting method and its ability for high protein or starch content, depending on its species and growing environment. The biofuels production from duckweed, is not only a solution to energy and environmental problems, but also a reliable way to realize the utilization of duckweed. This critical review focuses on the bio-oil production from duckweed via pyrolysis and hydrothermal liquefaction processes. First, characteristics and eco-environmental benefits of duckweed are reviewed. Next, the impacts of different parameters on the properties and distribution of bio-oil from pyrolysis and hydrothermal liquefaction are discussed in detail. Subsequently, the effect of hydrogen donor solvents (as reaction media for upgrading) and catalysts on the upgrading of duckweed bio-oil are extensively discussed. This paper ends with the prospects for further development in thermochemical valorization of duckweed.

Duckweeds: their utilization, metabolites and cultivation

Duckweeds are floating plants of the family Lemnaceae, comprising 5 genera and 36 species. They typically live in ponds or lakes and are found worldwide, except the polar regions. There are two duckweed subfamilies-namely Lemnoidea and Wolffioideae, with 15 and 21 species, respectively. Additionally, they have characteristic reproduction methods. Several metabolites have also been reported in various duckweeds. Duckweeds have a wide range of adaptive capabilities and are particularly suitable for experiments requiring high productivity because of their speedy growth and reproduction rates. Duckweeds have been studied for their use as food/feed resources and pharmaceuticals, as well as for phytoremediation and industrial applications. Because there are numerous duckweed species, culture conditions should be optimized for industrial applications. Here, we review and summarize studies on duckweed species and their utilization, metabolites, and cultivation methods to support the extended application of duckweeds in future.

Flavonoids from duckweeds: potential applications in the human diet

Duckweeds are the smallest free-floating flowering aquatic plants. Their biotechnological applications include their use as food, bioenergy, and environmental sustainability, as they can help clean polluted water. The high growth capacity and their chemical properties make them suitable for human health applications. Here we evaluated the ethanolic extracts from five species of duckweeds by HPLC-DAD/MS-MS for chemical characterization. Sixteen compounds were identified and quantified, in which three were chlorogenic acid derivatives and eleven apigenin and luteolin derivatives. We describe for the first time the presence in duckweeds of 5-O-(E)-caffeoylquinic acid (1), 3-O-(E)-coumaroylquinic acid (2), luteolin-7-O-glucoside-C-glucoside (3), 4-O-(E)-coumaroylquinic acid (4), luteolin-6-C-glucoside-8-C-rhamnoside (5), and luteolin-8-C-glucoside-6-C-rhamnoside (6). The flavonoids diversity showed a significant content of luteolin and its derivatives, except for Landoltia punctata that had significant apigenin content. Flavones identified in duckweeds were mostly C-glycosides, which can benefit human diets, and its abundance seems to be related to the higher antioxidant and anticancer capacities of Wolffiella caudata, Wolffia borealis, and Landoltia punctata. Our findings reinforce the idea that duckweeds could be valuable additives to the human diet, and their potential should be further explored.

Lemna minor studies under various storage periods using extended-polarity extraction and metabolite non-target screening analysis

Plant metabolomic studies cover a broad band of compounds, including various functional groups with different polarities and other physiochemical properties. For this reason, specific optimized methods are needed in order to enable efficient and non-destructive extraction of molecules over a large range of LogD values. This study presents a simple and efficient extraction procedure for Lemna minor samples demonstrating polarity extension of the molecular range. The Lemna samples chosen were kept under the following storage conditions: 1) fresh, 2) stored for a few days at -80 °C, and 3) stored for 6 months at -80 °C. The samples were extracted using five specifically chosen solvents: 100 % ethanol, 100 % methanol (MeOH), acidic 90 % MeOH (MeOH-water-formic acid (FAC) (90:9.5:0.5, v/v/v), MeOH-water (50:50, v/v), and 100 % water. The final extraction procedure was conducted subject to three solvent conditions, and the subsequent polarity-extended analysis was applied for Lemna minor samples using RPLC-HILIC-ESI-TOF-MS. The extraction yield is in descending order (acidic 90 % MeOH), 50 % MeOH, 100 % water and 100 % MeOH. The results displayed significant molecular differences, both in the extracts investigated and in the fresh Lemna samples, compared to stored samples, in terms of the extraction yield and reducing contents as well as the number of features. The storage of Lemna minor resulted in changes to the fingerprint of its metabolites as the reducing contents increased. The comparisons enable a direct view of molecule characterizations, in terms of their polarity, molecular mass, and signal intensity. This parametric information would appear ideal for further statistical data analysis. Consequently, the extraction procedure and the analysis/data evaluation are highly suitable for the so-called extended-polarity non-target screening procedure.

How do novel and conventional agri-food wastes, co-products and by-products improve soil functions and soil quality?

Agriculture is estimated to generate about 700 million tons of waste annually in the EU. Novel valorization technologies are developing continuously to recover and recycle valuable compounds and nutrients from waste materials. To close the nutrient loop, low-value agri-food wastes, co-products and by-products (AFWCBs) produced during the valorization process, need to be returned to the soil. However, knowledge on their reaction in soils that is needed to allow efficient and environmentally sound recycling is largely lacking. To this end, we set up a series of laboratory incubation experiments using 10 AFWCBs including insect frass residues made from three different feedstocks, anaerobic digestates from two feedstocks, potato-pulp, rice bran compost, duckweed and two reference crop residues (wheat straw and sugar beet) and measured net N release, C mineralization, dehydrogenase activity (DHA), microbial biomass C (MBC) and community structure. The suppressing potential of frasses and digestates against Rhizoctonia solani was determined using bean. The digestates released the highest net mineral N (50-70%) followed by rice bran compost (55%) and duckweed (30%), while frass made from general food waste and potato-pulp immobilized N like the reference straw for 91 days after incubation. All AFWCBs except digestates significantly increased MBC compared to the control while frasses, potato-pulp and duckweed increased DHA. Frasses and digestates significantly suppressed the development of Rhizoctonia solani in bean plants. AFWCBs from emerging valorizing technologies have the potential to improve microbial activities, C sequestration and may play a significant role in closing the nutrient loop.

Abscisic acid-enhanced starch accumulation of bioenergy crop duckweed (Spirodela polyrrhiza)

To meet the increasing energy consumption around the world and fight global climate change, there is an urgent need to explore renewable energy crops to replace the traditional energy sources. Duckweed (Spirodela polyrrhiza) is widely distributed in the world and has high starch and low lignin contents, which is perhaps an ideal feedstock for bioenergy production. To investigate the effects of abscisic acid (ABA) on duckweed biomass and starch accumulation, Spirodela polyrrhiza was cultivated at different ABA concentrations. The results showed that the highest starch content in duckweed (21.8% dry weight) was achieved in 1.0 × 10-2 mg L-1 ABA medium, 70.3% higher than that of the control medium without ABA. The number of starch granules in 1.0 × 10-2 mg L-1 ABA medium was far more than that in the control medium. The highest adenosine diphosphate (ADP)-glucose pyrophosphorylase (AGPase) activity was observed in the 1.0 × 10-2 mg L-1 ABA medium, which was caused by the up-regulation expression of ADP-glucose pyrophosphorylase 2 (APL2). Further investigations on cell ultra-structures and stomatal property of the duckweed indicated that ABA increased the number and size of starch granules and stomatal size in duckweed cells. These enhancements lead to a greatly improved energy flow in the aquatic plant from photosynthesis to carbon storage, making duckweed a potential renewable bioenergy crop.

Biosorptive removal of acid orange 74 dye by HCl-pretreated Lemna sp

Acid orange 74 (AO74) is a chromium-complex monoazo acid dye widely used in the textile industry. Due to being highly toxic and non-biodegradable, it must be removed from polluted water to protect the health of people and the environment. The aim of this study was two-fold: to evaluate the biosorption of AO74 from an aqueous solution by utilizing HCl-pretreated Lemna sp. (HPL), and to examine dye desorption from the plant material. The maximum capacity of AO74 biosorption (64.24 mg g^-1) was reached after 4 h at the most adequate pH, which was 2. The biosorption capacity decreased 25% (to 48.18 mg g^-1) during the second biosorption/desorption cycle and remained essentially unchanged during the third cycle. The pseudo-second-order kinetics model concurred well with the experimental results of assays involving various levels of pH in the eluent solution and distinct initial concentrations of AO74. NaOH (0.01 M) was the best eluent solution. The Toth isotherm model best described AO74 biosorption equilibrium data. FTIR analysis confirmed the crucial role of HPL proteins in AO74 biosorption. SEM-EDX and CLSM techniques verified the effective biosorption/desorption of the dye during the three cycles. Therefore, HPL has potential for the removal of AO74 dye from wastewaters.

Linkage structure of cell-wall polysaccharides from three duckweed species

Rapid growth and easily digestible walls that are naturally low in lignin make the aquatic plant family Lemnaceae, or duckweed, a promising feedstock for biofuel production. Monosaccharide and linkage analysis of cell walls from three species of duckweed: Spirodela polyrhiza, Lemna gibba, and Wolffia australiana showed that apiogalacturonans and/or xylogalacturonans, and smaller amounts of rhamnogalacturonan I, constituted 57%, 51% and 48% of their respective wall mass. Hemicellulosic xylan, xyloglucan, and glucomannan made up lesser amounts wall mass across the three species. Apiose residues were either non-reducing terminal or 3'-linked, but their ratios varied substantially from nearly 1:1 for S. polyrhiza and 2:1 for L. gibba, to 10:1 for W. australiana. These findings will help guide future research to design efficient strategies for disassembly of duckweed cell walls into sugars and uronic acids for conversion of duckweed biomass into usable fuel, and to facilitate extraction of other bioproducts from its polysaccharides.

Production of deuterated biomass by cultivation of Lemna minor (duckweed) in D2O

Common duckweed Lemna minor was cultivated in 50% D₂O to produce biomass with 50-60% deuterium incorporation containing cellulose with degree of polymerization close (85%) to that of H₂O-grown controls. The small aquatic plant duckweed, particularly the genus Lemna, widely used for toxicity testing, has been proposed as a potential source of biomass for conversion into biofuels as well as a platform for production of pharmaceuticals and specialty chemicals. Ability to produce deuterium-substituted duckweed can potentially extend the range of useful products as well as assist process improvement. Cultivation of these plants under deuterating conditions was previously been reported to require addition of kinetin to induce growth and was hampered by anomalies in cellular morphology and protein metabolism. Here, we report the production of biomass with 50-60% deuterium incorporation by long-term photoheterotrophic growth of common duckweed Lemna minor in 50% D₂O with 0.5% glucose. L. minor grown in 50% D₂O without addition of kinetin exhibited a lag phase twice that of H₂O-grown controls, before start of log phase growth at 40% of control rates. Compared to continuous white fluorescent light, growth rates increased fivefold for H₂O and twofold for 50% D₂O when plants were illuminated at higher intensity with a metal halide lamp and a diurnal cycle of 12-h light/12-h dark. Deuterium incorporation was determined by a combination of ¹H and ²H nuclear magnetic resonance (NMR) to be 40-60%. The cellulose from the deuterated plants had an average-number degree of polymerization (DP_n) and polydispersity index (PDI) close to that of H₂O-grown controls, while Klason lignin content was reduced. The only major gross morphological change noted was root inhibition.

Duckweed (Lemna minor) is a novel natural inducer of cellulase production in Trichoderma reesei

An inducer is crucial for cellulase production. In this study, duckweed was used as an inducer of cellulase production by Trichoderma reesei RUT C30. In a reaction induced by 50 g/L duckweed in shake flasks, the filter-paper activity (FPA) reached 6.5 FPU/mL, a value comparable to that induced by avicel. The enzyme-hydrolysis rate induced by steam-exploded corn stalk was 54.2%, representing a 28% improvement over that induced by avicel. The duckweed starch was hydrolyzed to glucose, which was subsequently used for biomass accumulation during the fermentation process. Furthermore, to optimize the control of the fermentation process, a combined substrate of avicel and duckweed was used to induce cellulase production by T. reesei RUT C30. The cellulase production and hydrolysis rates of the combined substrate, compared with avicel alone, were 39.6% and 36.7% higher, respectively. The results of this study suggest that duckweed is a good inducer of cellulase production in T. reesei, and it might aid in decreasing the cost of lignocellulosic materials hydrolysis.

Mass Production of Lemna minor and Its Amino Acid and Fatty Acid Profiles

The surface floating duckweed Lemna minor (Lemnaceae) is a potential ingredient to replace the application of fish-meal in the aqua-feed. The culture technique of the duckweed was standardized in outdoor tanks and then applied in the pond. Three consecutive experiments were conducted in tanks (1.2 × 0.35 × 0.3 m). In experiment 1, four different manures were used. In manure 1 (organic manure, OM) and manure 3 (2x OM), cattle manure, poultry droppings, and mustard oil cake (1:1:1) were used; in manure 2 (inorganic fertilizer, IF), urea, potash, triple superphosphate were used; manure 4 (2x OM+IF) was a combination of manure 2 and manure 3. In experiment 2, manure 1 (OM) and manure 2 (IF) were used, and manure 3 (OM+IF) was a combination of both manures. In experiment 3, OM and IF were selected. In pond (20 × 10 × 0.5 m), OM was applied. Fresh duckweed was seeded after 5 days of manure application. In experiments 1 and 3, total production was significantly (P < 0.05) higher in OM compared to other treatments. In experiment 2, there was no significant (P > 0.05) difference in production between OM and IF. In pond, relative growth rate (RGR) of duckweed ranged from 0.422 to 0.073 g/g/day and total production was 702.5 Kg/ha/month (dry weight). Protein, lipid, and ash contents were higher in duckweed cultured in OM compared to IF. The duckweed was a rich source of essential (39.20%), non-essential (53.64%), and non-proteinogenic (7.13%) amino acids. Among essential amino acids, leucine, isoleucine, and valine constituted 48.67%. Glutamic acid was 25.87% of total non-essential amino acids. Citrulline, hydroxiproline, taurine, etc. were found in the duckweed. The fatty acid composition was dominated by PUFA, 60–63% of total fatty acids, largely α-linolenic acid (LNA, 18:3n-3) at around 41 to 47% and linoleic acid (LA, 18:2n-6) at 17–18%. The nutritional value of duckweeds and their production potential in the pond conditions were evaluated. Duckweed biomass may thus be used to replace commercial fish-meal that is currently used in aquaculture.

Correlation of Apiose Levels and Growth Rates in Duckweeds

The carbon assimilated by photosynthesis in plants can be partitioned into starch, soluble sugars, and cell wall polymers. Higher levels of starch accumulation in leaves are usually correlated with a lower growth capacity. Duckweeds are fast-growing aquatic monocot plants that can accumulate high levels of starch. They are an unusual group because their cell wall has very low levels of lignin while accumulating apiogalacturonan, a pectic polysaccharide that could be involved with boron assimilation. In this work, five duckweed species from different genera (Spirodela polyrhiza, Landoltia punctata, Lemna gibba, Wolffiella caudata, and Wolffia borealis) were cultivated under two light intensities (20 and 500 μmoles of photons m⁻² s⁻¹) to evaluate the effects of growth rate on carbohydrate metabolism. A comparative analysis was performed by measuring their relative growth rates (RGR), and their content for starch, as well as soluble and cell wall carbohydrates. We found that the faster-growing species (the Lemnoideae) accumulate lower starch and higher soluble sugars than the slower-growing species within the Wolffioideae. Interestingly, analysis of the cell wall monosaccharides revealed that the slower-growing species displayed lower content of apiose in their walls. Our results indicate that higher accumulation of apiose observed in cell walls of the Lemnoideae species, which likely correlates with a higher proportion of apiogalacturonan, may lead to higher efficiency in the assimilation of boron. This is consistent with the increased RGR observed under conditions with higher apiose in the cell wall, such as higher light intensity. Consistent with their lower growth capacity, the Wolffioideae species we studied shows higher starch accumulation in comparison with the Lemnoideae species. We suggest that apiose levels could be good biomarkers for growth capacity of duckweeds and suggest that boron uptake could be an important factor for growth control in this aquatic plant family.

Efficient production of succinic acid from duckweed (Landoltia punctata) hydrolysate by Actinobacillus succinogenes GXAS137

A novel process of enzyme pretreatment and semi-simultaneous saccharification and fermentation (SSSF) was developed in this work to improve succinic acid (SA) productivity from duckweed (Landoltia punctata) and achieve low viscosity. Viscosity (83.86%) was reduced by the pretreatment with combined enzymes at 50 °C for 2 h to a greater extent than that by single enzyme (26.19-71.75%). SSSF was an optimal combination with 65.31 g/L of SA content, which was remarkably higher than those obtained through conventional separate hydrolysis and fermentation (62.12 g/L) and simultaneous saccharification and fermentation (52.41 g/L). The combined approach was effective for SA production. Approximately 75.46 g/L of SA content with a yield of 82.87% and a productivity of 1.35 g/L/h was obtained after 56 h in a 2 L bioreactor. Further studies will focus on increasing the working scale of the proposed method.

Cell wall reconstruction and DNA damage repair play a key role in the improved salt tolerance effects of He-Ne laser irradiation in tall fescue seedlings

The improved salt tolerance effects of He–Ne laser were further studied through the estimation of ROS levels, cell viability, DNA damage phenomena, physicochemical properties, and monosaccharide compositions of cell wall polysaccharides in tall fescue seedlings. Salt stress produced deleterious effects on seedlings growth and development. ROS levels and genomic DNA damage were markedly increased compared with controls. Physicochemical activities and monosaccharide proportions of cell wall polysaccharide were also pronouncedly altered. He–Ne laser irradiation improved plant growth retardation via increasing cell viability and reverting physicochemical parameters. According to the results of Fourier transform infrared (FTIR) scanning spectra and DNA apopladder analysis, He–Ne laser was showed to efficiently ameliorate cell wall polysaccharide damage and DNA fragmentation phenomena. The treatment with DNA synthesis inhibitor further demonstrated that DNA damage repair was correlated with the improvement effects of the laser. Therefore, our data illustrated that He–Ne laser irradiation resulted in cell wall reconstruction and genomic DNA injury repair in vivo in salt-stressed seedlings, then enhanced salt tolerance probably via interactions between plant cell wall and related resistance gene expression pattern.

Simultaneous saccharification and fermentation of steam exploded duckweed: Improvement of the ethanol yield by increasing yeast titre

This study investigated the conversion of Lemna minor biomass to bioethanol. The biomass was pre-treated by steam explosion (SE, 210°C, 10 min) and then subjected to simultaneous saccharification and fermentation (SSF) using Cellic® CTec 2 (20 U or 0.87 FPU g(-1) substrate) cellulase plus β-glucosidase (2 U g(-1) substrate) and a yeast inoculum of 10% (v/v or 8.0×10(7) cells mL(-1)). At a substrate concentration of 1% (w/v) an ethanol yield of 80% (w/w, theoretical) was achieved. However at a substrate concentration of 20% (w/v), the ethanol yield was lowered to 18.8% (w/w, theoretical). Yields were considerably improved by increasing the yeast titre in the inoculum or preconditioning the yeast on steam exploded liquor. These approaches enhanced the ethanol yield up to 70% (w/w, theoretical) at a substrate concentration of 20% (w/v) by metabolising fermentation inhibitors.