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Cadmium (Cd) hampers plant growth and harms photosynthesis. Glutamate (Glu) responds to Cd stress and activates the Ca[sup.2+] signaling pathway in duckweed, emphasizing Glu’s significant role in Cd stress. In this study, we overexpressed phosphoserine aminotransferase (PSAT), a crucial enzyme in Glu metabolism, in duckweed. We investigated the response of PSAT-transgenic duckweed to Cd stress, including growth, Glu metabolism, photosynthesis, antioxidant enzyme activity, Cd[sup.2+] flux, and gene expression. Remarkably, under Cd stress, PSAT-transgenic duckweed prevented root abscission, upregulated the expression of photosynthesis ability, and increased Chl a, Chl b, and Chl a + b levels by 13.9%, 7%, and 12.6%, respectively. Antioxidant enzyme activity (CAT and SOD) also improved under Cd stress, reducing cell membrane damage in PSAT-transgenic duckweeds. Transcriptomic analysis revealed an upregulation of Glu metabolism-related enzymes in PSAT-transgenic duckweed under Cd stress. Moreover, metabolomic analysis showed a 68.4% increase in Glu content in PSAT duckweed exposed to Cd. This study sheds novel insights into the role of PSAT in enhancing plant resistance to Cd stress, establishing a theoretical basis for the impact of Glu metabolism on heavy metal tolerance in plants.

Duckweeds—a group of floating leaf macrophytes from the family of Lemnaceae —have become a major area of interest in the fields of basic and applied aquatic sciences in recent decades, including their use in water purification. Aiming to fulfill one of the gaps in the role of light intensity in duckweed efficiency in organic matter removal, we carried out a laboratory experiment with the use of two duckweed species: Lemna minor and Spirodela polyrhiza . Our main finding was that the intensity of light has a positive effect on the process of water purification from organic compounds by Lemna minor . However, this was not applicable to Spirodela polyrhiza due to the fact that the growth of the species was inhibited by high light intensities.

Plant regeneration is important for vegetative propagation, detoxification and the obtain of transgenic plant. We found that duckweed regeneration could be enhanced by regenerating callus. However, very little is known about the molecular mechanism and the release of volatile organic compounds (VOCs). To gain a global view of genes differently expression profiles in callus and regenerating callus, genetic transcript regulation has been studied. Auxin related genes have been significantly down-regulated in regenerating callus. Cytokinin signal pathway genes have been up-regulated in regenerating callus. This result suggests the modify of auxin and cytokinin balance determines the regenerating callus. Volatile organic compounds release has been analysised by gas chromatography/ mass spectrum during the stage of plant regeneration, and 11 kinds of unique volatile organic compounds in the regenerating callus were increased. Cyclohexane treatment enhanced duckweed regeneration by initiating root. Moreover, Auxin signal pathway genes were down-regulated in callus treated by cyclohexane. All together, these results indicated that cyclohexane released by regenerating callus promoted duckweed regeneration. Our results provide novel mechanistic insights into how regenerating callus promotes regeneration.

Microplastics are widely spread in aquatic environments. Although they are considered among the most alarming contaminants, toxic effects on organisms are unclear, particularly on freshwater plants. In this study, the duckweed Lemna minuta was grown on different concentrations (50, 100 mg/L) of poly(styrene-co-methyl methacrylate) microplastics (MP) and exposure times (T0, T7, T14, T28 days). The phytotoxic effects of MP were investigated by analyzing several plant morphological and biochemical parameters (frond and root size, plant growth, chlorophyll, and malondialdehyde content). Observations by scanning electron microscope revealed MP adsorption on plant surfaces. Exposition to MP adversely affected plant growth and chlorophyll content with respect to both MP concentrations and exposure times. Conversely, malondialdehyde measurements did not indicate an alteration of oxidative lipid damage in plant tissue. The presence of MP induced root elongation when compared to the control plants. The effects of MP on L. minuta plants were more evident at T28. These results contribute to a better understanding of MP’s impact on aquatic plants and highlight that MP contamination manifests with chronic-type effects, which are thus detectable at longer exposure times of 7 days than those traditionally used in phytotoxicology tests on duckweeds.

Many phytochemicals can affect the growth and development of plants and insects which can be used as biological control agents. In this study, different concentrations of crude, hexane, chloroform, butanol, and aqueous extracts of Euphorbia nivulia Buch.-Ham., an endemic plant of the Cholistan desert in South Punjab of Pakistan, were analysed for their chemical constituents. Their various concentrations were also tested for their phytotoxic and insecticidal potential against duckweed, Lemna minor L., and the dusky cotton bug, Oxycarenus hyalinipennis Costa. various polyphenols, i.e., quercetin, gallic acid, caffeic acid, syringic acid, coumaric acid, ferulic acid, and cinnamic acid were detected in different concentrations with different solvents during the phytochemical screening of E . nivulia . In the phytotoxicity test, except for 100 μg/mL of the butanol extract gave 4.5% growth regulation, no phytotoxic lethality could be found at 10 and 100 μg/mL of all the extracts. The highest concentration, 1000 μg/mL, of the chloroform, crude, and butanol extracts showed 100, 63.1, and 27.1% of growth inhibition in duckweed, respectively. In the insecticidal bioassay, the highest O . hyalinipennis mortalities (87 and 75%) were recorded at 15% concentration of the chloroform and butanol extracts of E . nivulia . In contrast, the lower concentrations of the E . nivulia extracts caused the lower mortalities. Altogether, these findings revealed that E . nivulia chloroform extracts showed significant phytotoxicity while all the extracts showed insecticidal potential. This potential can be, further, refined to be developed for bio-control agents.

Industrial production of biogas offers a way to manage distillery leachate. The waste is usually subjected to anaerobic digestion for producing biogas. However, the effluent from anaerobic processes has high chemical oxygen demand (COD) and is harmful to the environment. An effective method of lowering COD is ozonation. Effluent from biogas plants after ozonation has the potential for use in breeding grounds for plants of the Lemnaceae family. Thus, they can provide a valuable additional source of biomass for the production of bioethanol. Lemna minor L. and Spirodela polyrhiza cultures were grown in media with the addition of 2.5% PFE, which had been treated by ozonation for between 6 and 50 min. Using ozonated effluent was an effective cultivation technique in all variants. The analyzed parameters were plant growth, chlorophyll index, fresh plant weight and photosynthetic traits (net photosynthesis, stomatal conductance, transpiration and concentration of intercellular CO2). The best growth of Lemna minor L. was observed in the media with PFE treated for 12 min. Similar effects were obtained for S. polyrhiza, with ozone treatment for 12 and 25 min. The results show the potential of using ozone-treated post-fermentation leachate as a supplement in culture media.

Pesticides represent a major human input into the ecosystem, posing a serious risk to non-target organisms. Therefore, there is pressure toward the reduction in their use and the discovery of alternative sources of bioactivity. Endophytic microorganisms represent a source of bioactivity, whose potential for plant protection has been recently established. In this context, an olive tree endophytic Bacillus sp. was isolated, exhibiting superior antifungal activity, mainly attributed to its major surfactin, iturin, and fengycin and the minor gageotetrin and bacilotetrin groups of lipopeptides (LP). Based on the potential of LP and the lack of information on their toxicity to aquatic organisms, we have investigated the toxicity of an LP extract to the model macrophyte Lemna minor L. The extract exhibited low phytotoxicity (EC[sub.50] = 419 μg·mL[sup.−1] ), and for the investigation of its effect on the plant, GC/EI/MS metabolomics was applied following exposure to sub-lethal doses (EC[sub.25] and EC[sub.50] ). Results revealed a general disturbance of plants’ biosynthetic capacity in response to LP treatments, with substantial effect on the amino acid pool and the defense mechanism regulated by jasmonate. There are no previous reports on the phytotoxicity of LP to L. minor, with evidence supporting their improved toxicological profile and potential in plant protection.

The use of clays as adsorbents and catalysts in the ozonation of organic pollutants (Atrazine, bis-Phenol A, Diazinon, and Diclofenac sodium) allowed simulating their natural oxidative degradation in clay soils and to evaluate the ecotoxicity of mixtures partially oxidized on the species Lemna minor, a biodiversity representative of plants in the aquatic environment. Kinetic data showed that the adsorption of organic pollutants on clay particles obeys the pseudo-second-order model, while the adsorption isotherms satisfactorily fit the Langmuir model. Adsorption reduces the dispersion of the organic pollutant in the environment and prolongs its persistence and its natural degradation probability. Measurements of the Zeta potential and particle size as a function of pH demonstrate that the catalytic activity of clay depends on its cation, its silica/alumina ratio, and therefore on its permanent and temporary ion exchange capacities. These factors seem to govern its delamination and dispersion in aqueous media, its hydrophilic-hydrophobic character, and its porosity. Tests conducted on Lemna minor in contact with ozonation mixtures revealed that the toxicity could be due to pH decrease and to the toxicity of the intermediates yielded. Ecotoxicity would depend on the structure of the organic molecules, the chemical composition of the clay surface and ozonation time, which determines the oxidation progress. These results are of great importance for further research because they allow concluding that the negative impact of the persistence of an organic molecule in clay-containing media depends on the type and composition of the very clay mineral.

ABSTRACT Plant growth-promoting bacteria (PGPB) have recently been demonstrated as a promising agent to improve wastewater treatment and biomass production efficiency of duckweed hydrocultures. With a view to their reliable use in aqueous environments, this study analysed the plant colonization dynamics of PGPB and the ecological consequences for the entire duckweed-associated bacterial community. A PGPB strain, Aquitalea magnusonii H3, was inoculated to duckweed at different cell densities or timings in the presence of three environmental bacterial communities. The results showed that strain H3 improved duckweed growth by 11.7–32.1% in five out of nine experiments. Quantitative-PCR and amplicon sequencing analyses showed that strain H3 successfully colonized duckweed after 1 and 3 d of inoculation in all cultivation tests. However, it significantly decreased in number after 7 d, and similar bacterial communities were observed on duckweed regardless of H3 inoculation. Predicted metagenome analysis suggested that genes related to bacterial chemotactic motility and surface attachment systems are consistently enriched through community assembly on duckweed. Taken together, strain H3 dominantly colonized duckweed for a short period and improved duckweed growth. However, the inoculation of the PGPB did not have a lasting impact due to the strong resilience of the natural duckweed microbiome. Duckweed microbiome can be modified for accelerated biomass production.

Sustainable management of leachate produced from the dumpsite is one of the major concerns in developing countries Aquatic plants such as duckweed have the potential to remove pollutants from wastewater which can also be cost-effective and feasible options for leachate treatment. Therefore, the objective of our present study was to examine the growth and nutrient removal efficiency of duckweed (Lemna minor) on leachate. Three tests were performed each by growing lemna minor on synthetic leachate under controlled conditions and on dumpsite leachate under natural conditions. During each test, duckweed was grown in 300 ml plastic containers with a surface area of 25.8 cm.sup.2 . About 60 mg of fresh mass of duckweed was grown on 250 ml leachate at an internal depth of 9.5 cm. Results revealed that, in comparison to synthetic leachate, duckweed removed Chemical Oxygen Demand (COD), nitrogen (N), and phosphorous (P) more efficiently from dumpsite leachate under natural climatic conditions. However, the amounts of N and P absorbed into duckweed body mass were about 16% and 35% respectively more at synthetic leachate under controlled conditions. Maximum growth rate of duckweed (7.03 g m.sup.-2 day.sup.-1) was also observed for synthetic leachate in comparison to the growth rate of 4.87 g m.sup.-2 day.sup.-1 at dumpsite leachate. Results of this study provide a useful interpretation of duckweed growth and nutrient removal dynamics from leachate under natural and laboratory conditions.