Functional Response (FR) and Relative Growth Rate (RGR) Do Not Show the Known Invasiveness of Lemna minuta (Kunth)

Ascorbic Acid Improves Tomato Salt Tolerance by Regulating Ion Homeostasis and Proline Synthesis

In this study, processing tomato (Solanum lycopersicum L.) 'Ligeer 87-5' was hydroponically cultivated under 100 mM NaCl to simulate salt stress. To investigate the impacts on ion homeostasis, osmotic regulation, and redox status in tomato seedlings, different endogenous levels of ascorbic acid (AsA) were established through the foliar application of 0.5 mM AsA (NA treatment), 0.25 mM lycorine (LYC, an inhibitor of AsA synthesis; NL treatment), and a combination of LYC and AsA (NLA treatment). The results demonstrated that exogenous AsA significantly increased the activities and gene expressions of key enzymes (L-galactono-1,4-lactone dehydrogenase (GalLDH) and L-galactose dehydrogenase (GalDH)) involved in AsA synthesis in tomato seedling leaves under NaCl stress and NL treatment, thereby increasing cellular AsA content to maintain its redox status in a reduced state. Additionally, exogenous AsA regulated multiple ion transporters via the SOS pathway and increased the selective absorption of K+, Ca2+, and Mg2+ in the aerial parts, reconstructing ion homeostasis in cells, thereby alleviating ion imbalance caused by salt stress. Exogenous AsA also increased proline dehydrogenase (ProDH) activity and gene expression, while inhibiting the activity and transcription levels of Δ1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine-δ-aminotransferase (OAT), thereby reducing excessive proline content in the leaves and alleviating osmotic stress. LYC exacerbated ion imbalance and osmotic stress caused by salt stress, which could be significantly reversed by AsA application. Therefore, exogenous AsA application increased endogenous AsA levels, reestablished ion homeostasis, maintained osmotic balance, effectively alleviated the inhibitory effect of salt stress on tomato seedling growth, and enhanced their salt tolerance.

Characterization of the cryptic interspecific hybrid Lemna×mediterranea by an integrated approach provides new insights into duckweed diversity

Lemnaceae taxonomy is challenged by the particular morphology of these tiny free-floating angiosperms. Although molecular taxonomy has helped clarify the phylogenetic history of this family, some inconsistency with morphological data leads to frequent misclassifications in the genus Lemna. Recently, the finding that Lemna japonica is an interspecific hybrid between Lemna minor and Lemna turionifera provided a clear explanation for one such taxonomic question. Here we demonstrated that L. minor is also capable of hybridizing with Lemna gibba, generating a cryptic but widespread taxon in the Mediterranean area. The nothotaxon Lemna ×mediterranea is described and compared with clones of the putative parental species L. minor and L. gibba. Genetic analysis by nuclear and plastid markers, as well as genome size measurement, revealed that two different cytotypes, diploid and triploid, originated by at least two independent hybridization events. Despite high overall similarity, morphometrical, physiological, and biochemical analyses showed an intermediate position of L. ×mediterranea between its parental species in most qualitative and quantitative characters, and also separation of the two hybrid cytotypes by some criteria. These data provide evidence that hybridization and polyploidization, driving forces of terrestrial plant evolution, contribute to duckweed genetic diversity and may have shaped the phylogenetic history of these mainly asexual, aquatic plants.

Characterization of the physico-chemical properties of the natural habitat and in vitro culture effects on the biochemistry, proliferation and morphology of Lemna minuta

In this study, the ecological conditions of the natural habitat of Lemna minuta Kunth in Morocco were investigated, and the impact of five synthetic growth media (Murashige-Skoog (MS), Schenk-Hildebrand (SH), Hoagland medium (HM), 10X Algal Assay Procedure (AAP), and Swedish Standard Institute medium (SIS)) on the morphophysiological and biochemical parameters was analysed. The morphophysiological parameters included root length, frond surface area, and fresh weight, while the biochemical parameters included photosynthetic pigments, carbohydrates, and protein content. The study was conducted in vitro in two phases: an uncontrolled aeration system (Phase I) and a controlled aeration system (Phase II).The results showed that the pH, conductivity, salinity, and ammonium levels in the natural habitat were within the optimal range for duckweed growth. The measured orthophosphate concentrations were higher compared to previous observations, while the recorded chemical oxygen demand values were low. The study also revealed a significant effect of the culture medium composition on the morphophysiological and biochemical parameters of the duckweed. The fresh weight biomass, relative growth rate in fronds, relative growth rate in surface area, root length, protein content, carbohydrates, chlorophyll (a), chlorophyll (b), total chlorophyll, carotenoids, and the chlorophyll (a/b) ratio were all affected by the culture medium.The most accurate regression models described the growth index GI(F) based on time and in vitro culture conditions in both phases. In Phase I, the best models for MS, SIS, AAP, and SH media were linear, weighted quadratic, cubic, and weighted cubic, respectively. In Phase II, the best models for all growth media were linear. The time coefficients (in days) for Phase II were 0.321, 0.547, 1.232, 1.470, and 0.306 for AAP, HM, MS, SH, and SIS, respectively.Comparing the morphophysiological and biochemical parameters of fronds from different media and analysing the regression model results showed that the SH and MS media were the best among the tested media for the in vitro culture of L. minuta in controlled aeration conditions. However, further research is needed to develop new synthetic media that best promote the growth and maintenance of this duckweed in long-term culture.

The genome and preliminary single-nuclei transcriptome of Lemna minuta reveals mechanisms of invasiveness

The ability to trace every cell in some model organisms has led to the fundamental understanding of development and cellular function. However, in plants the complexity of cell number, organ size, and developmental time makes this a challenge even in the diminutive model plant Arabidopsis (Arabidopsis thaliana). Duckweed, basal nongrass aquatic monocots, provide an opportunity to follow every cell of an entire plant due to their small size, reduced body plan, and fast clonal growth habit. Here we present a chromosome-resolved genome for the highly invasive Lesser Duckweed (Lemna minuta) and generate a preliminary cell atlas leveraging low cell coverage single-nuclei sequencing. We resolved the 360 megabase genome into 21 chromosomes, revealing a core nonredundant gene set with only the ancient tau whole-genome duplication shared with all monocots, and paralog expansion as a result of tandem duplications related to phytoremediation. Leveraging SMARTseq2 single-nuclei sequencing, which provided higher gene coverage yet lower cell count, we profiled 269 nuclei covering 36.9% (8,457) of the L. minuta transcriptome. Since molecular validation was not possible in this nonmodel plant, we leveraged gene orthology with model organism single-cell expression datasets, gene ontology, and cell trajectory analysis to define putative cell types. We found that the tissue that we computationally defined as mesophyll expressed high levels of elemental transport genes consistent with this tissue playing a role in L. minuta wastewater detoxification. The L. minuta genome and preliminary cell map provide a paradigm to decipher developmental genes and pathways for an entire plant.

Phytoremediation potential of the duckweeds Lemna minuta and Lemna minor to remove nutrients from treated waters

Phytoremediation potential of duckweeds (Lemna minuta, Lemna minor) to remove nutrients from simulated wastewater was analyzed. In two separate experiments, the two species were grown for 28 days in waters enriched with nitrate and phosphate to simulate nutrient concentrations of domestic wastewater. Water physical and chemical measurements (temperature, pH, conductivity, oxygen) and plant physiological and biochemical analysis (biomass, relative growth rate-RGR, nutrient and chlorophyll contents, peroxidative damage, bioconcentration factor-BCF) were made to test and compare the phytoremediation capacity of the two Lemna species. L. minuta biomass increased almost tenfold during the time-course of the treatment resulting in a doubling of the mat thickness and a RGR of 0.083 ± 0.001 g/g day. Maximum frond content of phosphate was reached by day 21 (increase over 165%) and nitrate by day 7 (10%). According to the BCF results (BCF > 1000), L. minuta was a hyperaccumulator for both nutrients. On the other hand, L. minor biomass and mat thickness decreased continuously during incubation (RGR = - 0.039 ± 0.004 g/g day). In L. minor fronds, phosphate content increased until day 14, after which there was a decrease until the end of the incubation. Frond nitrate content significantly decreased by day 7, but then remained relatively constant until the end of the experiment. L. minor proved to be hyperaccumulator for phosphates, but not for nitrates. Results indicated L. minuta has a greater potential than L. minor to remove both nutrients by bioaccumulation, especially phosphates, demonstrated also by better physiological and biochemical responses. However, during the incubation, the chlorophyll content of L. minuta mat did continuously decrease and peroxidative damage had increased until day 14, indicating that the system was under some kind of stress. Strategies to avoid this stress were discussed.

Application of common duckweed (Lemna minor) in phytoremediation of chemicals in the environment: State and future perspective

Over the past 50 years, different strategies have been developed for the remediation of polluted air, land and water. Driven by public opinion and regulatory bottlenecks, ecological based strategies are preferable than conventional methods in the treatments of chemical effluents. Ecological systems with the application of microbes, fungi, earthworms, plants, enzymes, electrode and nanoparticles have been applied to varying degrees in different media for the remediation of various categories of pollutants. Aquatic macrophytes have been used extensively for the remediation of pollutants in wastewater effluents and aquatic environment over the past 30 years with the common duckweed (L. minor) as one of the most effective macrophytes that have been applied for remediation studies. Duckweed has shown strong potentials for the phytoremediation of organic pollutants, heavy metals, agrochemicals, pharmaceuticals and personal care products, radioactive waste, nanomaterials, petroleum hydrocarbons, dyes, toxins, and related pollutants. This review covers the state of duckweed application for the remediation of diverse aquatic pollutants and identifies gaps that are necessary for further studies as we find pragmatic and sound ecological solutions for the remediation of polluted environment for sustainable development.

Adaptación del método Acreman para la limpieza de plantas en Lemna minuta (Araceae: Lemnoideae)

Lemna minuta es una macrófita flotante de amplia distribución en ecosistemas lénticos, que puede ser útil en el desarrollo de ex-perimentos ecofisiológicos y ecotoxicológicos debido a su potencial sensibilidad a contaminantes acuáticos como toxinas y meta-les pesados. Para estos, inicialmente se deben establecer cultivos axénicos con sus poblaciones bajo condiciones de laboratorio,los cuales requieren técnicas de limpieza para sus frondas que aún no han sido definidas. Se adaptó el método de Acreman en su tiempo de exposición y concentración de hipoclorito de sodio, propuesto para la desinfección de las especies pertenecientes al género LemnaL. (Lemnoideae) a partir de colonias nativas. Las colonias se obtuvieron de un humedal de la ciudad de Bogotá, y posteriormente se aclimataron y desinfectaron en diferentes tiempos y soluciones de hipoclorito. Los resultados más adecuadospara la remoción de algas epífitas y otros microrganismos de las frondas, sin presentar alta mortalidad de las colonias, se obtuvie-ron, respectivamente, en las concentraciones 0,5% (45 y 30segundos) y 0,25% (60segundos) de hipoclorito. Por el contrario, el tiempo  de  exposición  de  60segundos  propuesto  por  el  método  Acreman  (0,5%)  resultó  en  la  mortalidad  total  de  las  frondas (100%). Se sugiere utilizar una solución de hipoclorito de sodio 0,5% en un tiempo de exposición menor o igual a 45 segundos para la desinfección de colonias de L. minutacon fines experimentales.

Linking mode of action of the model respiratory and photosynthesis uncoupler 3,5-dichlorophenol to adverse outcomes in Lemna minor

Standard chemical toxicity testing guidelines using aquatic plant Lemna minor have been developed by several international standardisation organisations. Although being highly useful for regulatory purposes by focusing on traditional adverse endpoints, these tests provide limited information about the toxic mechanisms and modes of action (MoA). The present study aimed to use selected functional assays in L. minor after exposure to 3,5-dichlorophenol (3,5-DCP) as a model to characterise the toxic mechanisms causing growth inhibition and lethality in primary producers. The results demonstrated that 3,5-DCP caused concentration-dependent effects in chloroplasts and mitochondria. Uncoupling of oxidative phosphorylation (OXPHOS), reduction in chlorophyll (Chlorophyll a and b) content, reproduction rate and frond size were the most sensitive endpoints, followed by formation of reactive oxygen species (ROS), lipid peroxidation (LPO), reduction of carotenoid content and impairment of photosynthesis efficiency. Suppression of photosystem II (PSII) efficiency, electron transport rate (ETR), chlorophyll (a and b) contents and oxidative phosphorylation (OXPHOS) were closely correlated while ROS production and LPO were negative correlated with ETR, carotenoid content and growth parameters. A network of conceptual Adverse Outcome Pathways (AOPs) was developed to decipher the causal relationships between molecular, cellular, and apical adverse effects occurring in L. minor to form a basis for future studies with similar compounds.