Abundant Allelochemicals and the Inhibitory Mechanism of the Phenolic Acids in Water Dropwort for the Control of Microcystis aeruginosa Blooms

In recent years, with the frequent global occurrence of harmful algal blooms, the use of plant allelopathy to control algal blooms has attracted special and wide attention. This study validates the possibility of turning water dropwort into a biological resource to inhibit the growth of harmful Microcystis aeruginosa blooms via allelopathy. The results revealed that there were 33 types of allelopathic compounds in the water dropwort culture water, of which 15 were phenolic acids. Regarding water dropwort itself, 18 phenolic acids were discovered in all the organs of water dropwort via a targeted metabolomics analysis; they were found to be mainly synthesized in the leaves and then transported to the roots and then ultimately released into culture water where they inhibited M. aeruginosa growth. Next, three types of phenolic acids synthesized in water dropwort, i.e., benzoic, salicylic, and ferulic acids, were selected to clarify their inhibitory effects on the growth of M. aeruginosa and their mechanism(s) of action. It was found that the inhibitory effect of phenolic acids on the growth of M. aeruginosa increased with the increase of the exposure concentration, although the algae cells were more sensitive to benzoic acid than to salicylic and ferulic acids. Further study indicated that the inhibitory effects of the three phenolic acids on the growth of M. aeruginosa were largely due to the simultaneous action of reducing the number of cells, damaging the integrity of the cell membrane, inhibiting chlorophyll a (Chl-a) synthesis, decreasing the values of F0 and Fv/Fm, and increasing the activity of the antioxidant enzymes (SOD, POD, and CAT) of M. aeruginosa. Thus, the results of this study indicate that both culture water including the rich allelochemicals in water dropwort and biological algae inhibitors made from water dropwort could be used to control the growth of noxious algae in the future.

Integrative genome, transcriptome, microRNA, and degradome analysis of water dropwort (Oenanthe javanica) in response to water stress

Water dropwort (Liyang Baiqin, Oenanthe javanica (BI.) DC.) is an aquatic perennial plant from the Apiaceae family with abundant protein, dietary fiber, vitamins, and minerals. It usually grows in wet soils and can even grow in water. Here, whole-genome sequencing of O. javanica via HiSeq 2000 sequencing technology was reported for the first time. The genome size was 1.28 Gb, including 42,270 genes, of which 93.92% could be functionally annotated. An online database of the whole-genome sequences of water dropwort, Water dropwortDB, was established to share the results and facilitate further research on O. javanica (database homepage: http://apiaceae.njau.edu.cn/waterdropwortdb). Water dropwortDB offers whole-genome and transcriptome sequences and a Basic Local Alignment Search Tool. Comparative analysis with other species showed that the evolutionary relationship between O. javanica and Daucus carota was the closest. Twenty-five gene families of O. javanica were found to be expanded, and some genetic factors (such as genes and miRNAs) related to phenotypic and anatomic differentiation in O. javanica under different water conditions were further investigated. Two miRNA and target gene pairs (miR408 and Oja15472, miR171 and Oja47040) were remarkably regulated by water stress. The obtained reference genome of O. javanica provides important information for future work, thus making in-depth genetic breeding and gene editing possible. The present study also provides a foundation for the understanding of the O. javanica response to water stress, including morphological, anatomical, and genetic differentiation.

Comparative Transcriptomic Analysis Provides Novel Insights into the Blanched Stem of Oenanthe javanica

In the agricultural field, blanching is a technique used to obtain tender, sweet, and delicious water dropwort stems by blocking sunlight. The physiological and nutritional parameters of blanched water dropwort have been previously investigated. However, the molecular mechanism of blanching remains unclear. In the present study, we investigated transcriptomic variations for different blanching periods in the stem of water dropwort (pre, mid, post-blanching, and control). The results showed that many genes in pathways, such as photosynthesis, carbon fixation, and phytohormone signal transduction as well as transcription factors (TFs) were significantly dysregulated. Blanched stems of water dropwort showed the higher number of downregulated genes in pathways, such as photosynthesis, antenna protein, carbon fixation in photosynthetic organisms, and porphyrin and chlorophyll metabolism, which ultimately affect the photosynthesis in water dropwort. The genes of hormone signal transduction pathways (ethylene, jasmonic acid, brassinosteroid, and indole-3-acetic acid) showed upregulation in the post-blanched water dropwort plants. Overall, a higher number of genes coding for TFs, such as ERF, BHLH, MYB, zinc-finger, bZIP, and WRKY were overexpressed in blanched samples in comparison with the control. These genes and pathways participate in inducing the length, developmental processes, pale color, and stress tolerance of the blanched stem. Overall, the genes responsive to blanching, which were identified in this study, provide an effective foundation for further studies on the molecular mechanisms of blanching and photosynthesis regulations in water dropwort and other species.

A New Green Model for the Bioremediation and Resource Utilization of Livestock Wastewater

The rapid growth of the livestock and poultry industries has resulted in the production of a large amount of wastewater, and the treatment of this wastewater requires sustainable and environmentally friendly approaches such as phytoremediation. A substrate-free floating wetland planted with water dropwort (Oenanthe javanica), a common vegetable in Southeast China, was constructed to purify a lagoon with anaerobically and aerobically treated swine wastewater in Suqian, China. The average removal rates of total nitrogen, ammonium nitrogen, nitrite nitrogen, and chemical oxygen demand were 79.96%, 95.04%, 86.14%, and 59.91%, respectively, after 40 days of treatment. A total of 98.18 g∙m−2 nitrogen and 19.84 g∙m−2 phosphorus were absorbed into plants per harvest through the rapid growth of water dropwort biomass, and the nitrogen accumulation ability was similar to that observed of other plants, such as water hyacinth. In addition, the edible part of water dropwort was shown to comply with the Chinese National Food Sanitation Standards and be safe for human consumption. Its low soluble sugar content also makes it a suitable addition to the daily diet. Overall, substrate-free floating constructed wetlands planted with water dropwort could be more widely used for livestock wastewater purification and could be integrated with plant–livestock production in China because of its high removal efficiency and recycling utilization of water dropwort biomass.

Uncovering phylogenetic relationships and genetic diversity of water dropwort using phenotypic traits and SNP markers

The water dropworts Oenanthe linearis Wall. ex DC. and O. javanica (Blume) DC. are aquatic perennial herbs that have been used in China as vegetables and traditional medicines. However, their phylogenetic relationships and genetic diversity are poorly understood. Here, we presented the phenotypic traits and genome-wide DNA marker-based analysis of 158 water dropwort accessions representing both species. The analysis revealed that Oenanthe linearis was readily segregated into linear-leaf and deep-cleft leaf water dropworts according to their leaf shapes at flowering. Oenanthe javanica was classified by clustering analysis into two clusters based mainly on the morphological characteristics of their ultimate segments (leaflets). A set of 11 493 high-quality single-nucleotide polymorphisms was identified and used to construct a phylogenetic tree. There was strong discrimination between O. linearis and O. javanica, which was consistent with their phenotype diversification. The population structure and phylogenetic tree analyses suggested that the O. linearis accessions formed two major groups, corresponding to the linear-leaf and deep-cleft leaf types. The most obvious phenotypic differences between them were fully expressed at the reproductive growth stage. A single-nucleotide polymorphism-based analysis revealed that the O. javanica accessions could be categorized into groups I andII. However, this finding did not entirely align with the clusters revealed by morphological classification. Landraces were clustered into one group along with the remaining wild accessions. Hence, water dropwort domestication was short in duration. The level of genetic diversity for O. linearis (π = 0.1902) was slightly lower than that which was estimated for O. javanica (π = 0.2174). There was a low level of genetic differentiation between O. linearis and O. javanica (Fst = 0.0471). The mean genetic diversity among accessions ranged from 0.1818 for the linear-leaf types to 0.2318 for the groupII accessions. The phenotypic traits and the single-nucleotide polymorphism markers identified here lay empirical foundation for future genomic studies on water dropwort.

Effect of Salt Stress on Growth, Physiological Parameters, and Ionic Concentration of Water Dropwort (Oenanthe javanica) Cultivars

Salt stress is an important environmental limiting factor. Water dropwort (Oenanthe javanica) is an important vegetable in East Asia; however, its phenotypic and physiological response is poorly explored. For this purpose, 48 cultivars of water dropwort were grown hydroponically and treated with 0, 50, 100, and 200 mm NaCl for 14 days. Than their phenotypic responses were evaluated, afterward, physiological studies were carried out in selected sensitive and tolerant cultivars. In the present study, the potential tolerant (V11E0022) and sensitive (V11E0135) cultivars were selected by screening 48 cultivars based on their phenotype under four different levels of salt concentrations (0, 50, 100, and 200 mm). The results depicted that plant height, number of branches and leaves were less effected in V11E0022, and most severe reduction was observed in V11E0135 in comparison with others. Than the changes in biomass, ion contents, accumulation of reactive oxygen species, and activities of antioxidant enzymes and non-enzymatic antioxidants were determined in the leaves and roots of the selected cultivars. The potential tolerant cultivar (V11E0022) showed less reduction of water content and demonstrated low levels of Na+ uptake, malondialdehyde, and hydrogen peroxide (H2O2) in both leaves and roots. Moreover, the tolerant cultivar (V11E0022) showed high antioxidant activities of ascorbate peroxidase (APX), superoxide dismutase, peroxidase, catalase (CAT), reduced glutathione (GSH), and high accumulation of proline and soluble sugars compared to the sensitive cultivar (V11E0135). These results suggest the potential tolerance of V11E0022 cultivar against salt stress with low detrimental effects and a good antioxidant defense system. The observations also suggest good antioxidant capacity of water dropwort against salt stress. The findings of the present study also suggest that the number of branches and leaves, GSH, proline, soluble sugars, APX, and CAT could serve as the efficient markers for understanding the defense mechanisms of water dropwort under the conditions of salt stress.

Phenotypic, Nutritional, and Antioxidant Characterization of Blanched Oenanthe javanica for Preferable Cultivar

Blanching is a technique used in blocking sunlight for the production of tender, sweet, and delicious stems in the field. This technique is also used in water dropwort (Oenanthe javanica), an important vegetable in East Asia. In China, the steamed stems of water dropwort are prepared with boiled rice. However, the effect of blanching on the nutritional level and antioxidant capacity of water dropwort has not been explored yet. The current study aims to determine the nutrient contents and antioxidant capacities of five cultivars and select the best cultivar. They were mainly compared in terms of phenotypic, physiological, nutritional, and antioxidant levels after blanch cultivation. Results indicate that blanching significantly influenced the phenotype, physiology, and nutritional level of water dropwort in all cultivars. Although few parameters decreased with blanching, starch, sugars, vitamins, minerals, and antioxidant activities increased significantly in the blanched stems in mid- and post-blanching periods. The most noticeable changes were detected in post-blanching samples. Furthermore, the best cultivar (V11E0012) was identified among them. Therefore, blanched water dropwort could be consumed for achieving more nutraceuticals and antioxidants, and cultivar V11E0012 could be recommend for blanching cultivation.

Investigation of an Antioxidative System for Salinity Tolerance in Oenanthe javanica

Abiotic stress, such as drought and salinity, severely affect the growth and yield of many plants. Oenanthe javanica (commonly known as water dropwort) is an important vegetable that is grown in the saline-alkali soils of East Asia, where salinity is the limiting environmental factor. To study the defense mechanism of salt stress responses in water dropwort, we studied two water dropwort cultivars, V11E0022 and V11E0135, based on phenotypic and physiological indexes. We found that V11E0022 were tolerant to salt stress, as a result of good antioxidant defense system in the form of osmolyte (proline), antioxidants (polyphenols and flavonoids), and antioxidant enzymes (APX and CAT), which provided novel insights for salt-tolerant mechanisms. Then, a comparative transcriptomic analysis was conducted, and Gene Ontology (GO) analysis revealed that differentially expressed genes (DEGs) involved in the carbohydrate metabolic process could reduce oxidative stress and enhance energy production that can help in adaptation against salt stress. Similarly, lipid metabolic processes can also enhance tolerance against salt stress by reducing the transpiration rate, H2O2, and oxidative stress. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that DEGs involved in hormone signals transduction pathway promoted the activities of antioxidant enzymes and reduced oxidative stress; likewise, arginine and proline metabolism, and flavonoid pathways also stimulated the biosynthesis of proline and flavonoids, respectively, in response to salt stress. Moreover, transcription factors (TFs) were also identified, which play an important role in salt stress tolerance of water dropwort. The finding of this study will be helpful for crop improvement under salt stress.

Hypoglycemic effects of phenolic compound-rich aqueous extract from water dropwort (Oenanthe javanica DC.) on streptozotocin-induced diabetic mice

Phenolic compounds in water dropwort aqueous extract were identified, and the IRS-2/PI3K-AKT pathway and GLUT4 translocation were regulated for hypoglycemic action.

Therapeutic potency of fermented field water-dropwort (Oenanthe javanica (Blume) DC.) in ethanol-induced liver injury

Alcohol overconsumption and abuse leads to alcoholic liver disease (ALD), which is a major chronic liver disease worldwide.