Identification of a novel marker and its associated laccase gene for regulating ear length in tropical and subtropical maize lines.

KEY MESSAGE: This study revealed the identification of a novel gene, Zm00001d042906, that regulates maize ear length by modulating lignin synthesis and reported a molecular marker for selecting maize lines with elongated ears. Maize ear length has garnered considerable attention due to its high correlation with yield. In this study, six maize inbred lines of significant importance in maize breeding were used as parents. The temperate maize inbred line Ye107, characterized by a short ear, was crossed with five tropical or subtropical inbred lines featuring longer ears, creating a multi-parent population displaying significant variations in ear length. Through genome-wide association studies and mutation analysis, the A/G variation at SNP_183573532 on chromosome 3 was identified as an effective site for discriminating long-ear maize. Furthermore, the associated gene Zm00001d042906 was found to correlate with maize ear length. Zm00001d042906 was functionally annotated as a laccase (Lac4), which showed activity and influenced lignin synthesis in the midsection cells of the cob, thereby regulating maize ear length. This study further reports a novel molecular marker and a new gene that can assist maize breeding programs in selecting varieties with elongated ears.

Rho2 involved in development, stress response and pathogenicity of Fusarium oxysporum.

Rho GTPases regulate the activity of cell wall biosynthesis, actin assembly and polar cell secretion. However, the function of Rho GTPase in filamentous fungi is poorly understood. To understand the role of Rho2 GTPase in Fusarium oxysporum, which is one of root rot pathogens of Panax notoginseng, △rho2 mutant was constructed. Phenotypes of △rho2, including conidiation, germination of spores, stresses (osmotic-, cell membrane-, cell wall disturbing-, metal-, and high temperature-) tolerance and pathogenicity were analyzed. The results showed that the growth of △rho2 was destroyed under cell wall disturbing stress and high temperature stress, suggesting that Rho2 regulated the response of F. oxysporum to cell wall synthesis inhibitors and high temperature stress. Germination of spores and pathogenicity to P. notoginseng were reduced in △rho2 mutant. Western blot results showed that rho2 deletion increased the phosphorylation level of Mpk1. To identify genes regulated by Rho2, transcriptome sequencing was carried out. 2477 genes were identified as upregulated genes and 2177 genes were identified as downregulated genes after rho2 was deleted. These genes provide clues for further study of rho2 function.

14-3-3 proteins regulate the HCHO stress response by interacting with AtMDH1 and AtGS1 in tobacco and Arabidopsis.

Formaldehyde (HCHO) is one of the most essential common carcinogenic environmental pollutants. While 14-3-3 proteins are known to regulate the response of plants to HCHO stress, the regulatory mechanisms responsible for a tolerant phenotype remain unclear. We first performed qPCR analysis of HCHO-treated Arabidopsis and tobacco and determined that the expression of At14-3-3PSI and Nt14-3-3C genes was rapidly upregulated after HCHO stress. Furthermore, overexpression of 14-3-3, AtMDH1 or AtGS1 genes enhanced plant HCHO absorption capacity and resistance, and knockdown or knockout of 14-3-3, AtMDH1 or AtGS1 genes reduced plant HCHO absorption capacity and resistance. However, overexpression of the AtGS1 and AtMDH1 genes in the At14-3-3 psi mutant restored HCHO uptake and resistance in Arabidopsis. Moreover, 14-3-3 bound to the N-terminus of AtMDH1 and the C-terminus of AtGS1, respectively, and repressed and enhanced their expression. The 13C NMR results of HCHO stress mutants Atgs1 and Atmdh1 showed that the metabolites Glu and Asp rapidly increased, indicating that AtGS1 and AtMDH1 were indeed indispensable for Arabidopsis to metabolize HCHO. In conclusion, we uncovered a HCHO stress response mechanism mediated by 14-3-3, which enhances the plant's ability to absorb HCHO, deepening our understanding of how plants respond to HCHO stress.

Mapping of Lymph Node Metastasis and Efficacy Index in Thoracic Esophageal Squamous Cell Carcinoma: A Large-Scale Retrospective Analysis.

BACKGROUND: Esophageal squamous cell carcinoma has a high mortality rate in China. The metastatic pattern in the lymph nodes and the value of their dissection on the overall survival of these patients remain controversial. The primary aim of this study was to provide a basis for accurate staging of esophageal cancer and to identify the relationship between esophageal cancer surgery, lymph node dissection, and overall survival rates. METHODS: We utilized our hospital database to retrospectively review the data of 1727 patients with esophageal cancer who underwent R0 esophagectomy from January 2010 to December 2017. The lymph nodes were defined according to Japanese Classification of Esophageal Cancer, 11th Edition. The Efficacy Index (EI) was calculated by multiplying the frequency (%) of metastases to a zone and the 5-year survival rate (%) of patients with metastases to that zone, and then dividing by 100. RESULTS: The EI was high in the supraclavicular and mediastinal zones in patients with upper esophageal tumors, and the EI of 101R was 17.39, which was the highest among the lymph node stations. In patients with middle esophageal tumors, the EI was highest in the mediastinal zone, followed by the celiac and supraclavicular zones. Furthermore, the EI was highest in the celiac zone, followed by the mediastinal zones in patients with lower esophageal tumors. CONCLUSIONS: The EI of resected lymph nodes was found to vary between stations and was related to the primary location of the tumor.

Resected lymph nodes and survival of patients with esophageal squamous cell carcinoma: an observational study.

BACKGROUND: The incidence and mortality of esophageal cancer are high. Therefore, the authors aimed to investigate how the number of dissected lymph nodes (LNs) during esophagectomy for esophageal squamous cell carcinoma impacts overall survival (OS), particularly that of patients with positive LNs. MATERIALS AND METHODS: Data from 2010 to 2017 were obtained from the Sichuan Cancer Hospital and Institute Esophageal Cancer Case Management Database. Participants were divided into two groups: patients with negative lymph nodes (N0) and patients with positive lymph nodes (N+). The median number of resected LNs during surgery was 24; therefore, patients with 15-23 and those with 24 or more resected LNs were assigned to subgroups A and B, respectively. RESULTS: After a median follow-up of 60.33 months, 1624 patients who underwent esophagectomy were evaluated; 60.53 and 39.47% had a pathological diagnosis of N+ or N0, respectively. The median OS was 33.9 months for the N+ group; however, the N0 group did not achieve the median OS. The mean OS was 84.9 months. In the N+ group, the median OS times of subgroups A and B were 31.2 and 37.1 months, respectively. The OS rates at 1, 3, and 5 years were 82, 43, and 34%, respectively, for subgroup A of the N+ group; they were 86, 51, and 38%, respectively, for subgroup B of the N+ group. Subgroups A and B of the N0 group exhibited no statistically significant differences. CONCLUSION: Increasing the number of LNs harvested during surgery to 24 or more could improve the OS of patients with positive LNs but not that of patients with negative LNs.

Whole genome sequencing and analysis of Armillaria gallica Jzi34 symbiotic with Gastrodia elata.

BACKGROUND: Armillaria species are plant pathogens, but a few Armillaria species can establish a symbiotic relationship with Gastrodia elata, a rootless and leafless orchid, that is used as a Chinese herbal medicine. Armillaria is a nutrient source for the growth of G. elata. However, there are few reports on the molecular mechanism of symbiosis between Armillaria species and G. elata. The genome sequencing and analysis of Armillaria symbiotic with G. elata would provide genomic information for further studying the molecular mechanism of symbiosis. RESULTS: The de novo genome assembly was performed with the PacBio Sequel platform and Illumina NovaSeq PE150 for the A. gallica Jzi34 strain, which was symbiotic with G. elata. Its genome assembly contained ~ 79.9 Mbp and consisted of 60 contigs with an N50 of 2,535,910 bp. There were only 4.1% repetitive sequences in the genome assembly. Functional annotation analysis revealed a total of 16,280 protein coding genes. Compared with the other five genomes of Armillaria, the carbohydrate enzyme gene family of the genome was significantly contracted, while it had the largest set of glycosyl transferase (GT) genes. It also had an expansion of auxiliary activity enzymes AA3-2 gene subfamily and cytochrome P450 genes. The synteny analysis result of P450 genes reveals that the evolutionary relationship of P450 proteins between A. gallica Jzi34 and other four Armillaria was complex. CONCLUSIONS: These characteristics may be beneficial for establishing a symbiotic relationship with G. elata. These results explore the characteristics of A. gallica Jzi34 from a genomic perspective and provide an important genomic resource for further detailed study of Armillaria. This will help to further study the symbiotic mechanism between A. gallica and G. elata.

Impact of two­field or three­field lymphadenectomy on overall survival in middle and lower thoracic esophageal squamous cell carcinoma: A single­center retrospective analysis.

Squamous cell carcinoma is the main subtype of esophageal cancer in East Asia. The effect of the number of lymph nodes (LNs) removed to treat middle and lower thoracic esophageal squamous cell carcinoma (ESCC) in China remains controversial. Therefore, the present study aimed to investigate the impact of the number of LNs removed during lymphadenectomy on the survival of patients with middle and lower thoracic ESCC. Data were obtained from the Sichuan Cancer Hospital and Institute Esophageal Cancer Case Management Database from January 2010 to April 2020. Either three-field systematic lymphadenectomy (3F group) or two-field systematic lymphadenectomy (2F group) was performed for ESCC cases with or without suspicious tumor-positive cervical LNs, respectively. Subgroups were designed for further analysis based on the quartile number of resected LNs. After 50.7 months of median follow-up, 1,659 patients who underwent esophagectomy were enrolled. The median overall survival (OS) of the 2F and 3F groups was 50.0 months and 58.5 months, respectively. The OS rates at 1, 3 and 5 years were 86, 57 and 47%, respectively, in the 2F group, and 83, 52 and 47%, respectively, in the 3F group (P=0.732). The average OS of the 3F B and D groups was 57.7 months and 30.2 months, respectively (P=0.006). In the 2F group, the OS between subgroups was not significantly different. In conclusion, resection of >15 LNs during two-field dissection in patients with ESCC undergoing esophagectomy did not affect their survival outcomes. In three-field lymphadenectomy, the extent of LNs removed could lead to different survival outcomes.

Overexpression of tomato glutathione reductase (SlGR) in transgenic tobacco enhances salt tolerance involving the S-nitrosylation of GR.

S-nitrosylation, a post-translational modification (PTM) dependent on nitric oxide, is essential for plant development and environmental responsiveness. However, the function of S-nitrosylation of glutathione reductase (GR) in tomato (SlGR) under NaCl stress is yet uncertain. In this study, sodium nitroprusside (SNP), an exogenous NO donor, alleviated the growth inhibition of tomato under NaCl treatment, particularly at 100 µM. Following NaCl treatment, the transcripts, enzyme activity, and S-nitrosylated level of GR were increased. In vitro, the SlGR protein was able to be S-nitrosylated by S-nitrosoglutathione (GSNO), significantly increasing the activity of GR. SlGR overexpression transgenic tobacco plants exhibited enhanced germination rate, fresh weight, and increased root length in comparison to wild-type (WT) seedlings. The accumulation of reactive oxygen species (ROS) was lower, whereas the expression and activities of GR, ascorbate peroxidase (APX), superoxide dismutase (SOD), and catalase (CAT); the ratio of ascorbic acid/dehydroascorbic acid (AsA/DHA), reduced glutathione/oxidized glutathione (GSH/GSSG), total soluble sugar and proline contents; and the expression of stress-related genes were higher in SlGR overexpression transgenic plants in comparison to the WT plants following NaCl treatment. The accumulation of NO and S-nitrosylated levels of GR in transgenic plants was higher in comparison to WT plants following NaCl treatment. These results indicated that S-nitrosylation of GR played a significant role in salt tolerance by regulating the oxidative state.

Optimal discharge planning for esophagectomy patients with enhanced recovery after surgery: Recommendations.

Background: Studies have suggested that the postoperative length of stay (PLOS) of esophagectomy patients under the enhanced recovery after surgery (ERAS) pathway should be >10 days as against the previously recommended 7 days. We investigated the distribution and influencing factors of PLOS in the ERAS pathway in order to recommend an optimal planned discharge time. Methods: This was a single-center retrospective study of 449 patients with thoracic esophageal carcinoma who underwent esophagectomy and perioperative ERAS between January 2013 and April 2021. We established a database to prospectively document the causes of delayed discharge. Results: The mean and median PLOS were 10.2 days and 8.0 days (range: 5-97), respectively. Patients were divided into four groups: group A (PLOS ≤ 7 days), 179 patients (39.9%); group B (8 ≤ PLOS ≤ 10 days), 152 (33.9%); group C (11 ≤ PLOS ≤ 14 days), 68 (15.1%); group D (PLOS > 14 days), 50 patients (11.1%). The main cause of prolonged PLOS in group B was minor complications (prolonged chest drainage, pulmonary infection, recurrent laryngeal nerve injury). Severely prolonged PLOS in groups C and D were due to major complications and comorbidities. On multivariable logistic regression analysis, open surgery, surgical duration >240 min, age >64 years, surgical complication grade >2, and critical comorbidities were identified as risk factors for delayed discharge. Conclusions: The optimal planned discharge time for patients undergoing esophagectomy with ERAS should be 7-10 days with a 4-day discharge observation window. Patients at risk of delayed discharge should be managed adopting PLOS prediction.

Enhancement production of lipid and unsaturation of fatty acids in Cryptococcus humicola via addition of calcium ion.

Lipids synthesized by oleaginous yeasts are considered to be the best candidates for biodiesel production. Cryptococcus humicola as an oleaginous yeast accumulated lipid in cells. In order to optimize the conditions for lipid production, different carbon and nitrogen sources were used and metals were added into the medium. Ca2+ addition increased the lipid production greatly. Xylose and peptone were optimal carbon source and nitrogen source, respectively for lipid accumulation. Response surface experiment results revealed that the accumulation of lipid could be maximized when the xylose, peptone and Ca2+ concentration was 61 g/L, 4.31 g/L, 0.67 mmol/L. C16 and C18 fatty acid account for about 91% of the total fatty acids. The most abundant fatty acid was oleic acid (42.68%), followed by palmitic acid (29.7%) and stearic acid (13.87%). The addition of Ca2+ increased the content of unsaturated fatty acids (such as C16:1 and C18:1) and improved the unsaturation of fatty acids. Quantitative real time PCR analysis revealed that expression of genes related to lipid biosynthesis showed up-regulated by Ca2+ treatment. This study provided a strategy for increase in lipid production and content of unsaturated fatty acids.

Transcriptome analysis reveals the regulatory mode by which NAA promotes the growth of Armillaria gallica.

A symbiotic relationship is observed between Armillaria and the Chinese herbal medicine Gastrodia elata (G. elata). Armillaria is a nutrient source for the growth of G. elata, and its nutrient metabolism efficiency affects the growth and development of G. elata. Auxin has been reported to stimulate Armillaria species, but the molecular mechanism remains unknown. We found that naphthalene acetic acid (NAA) can also promote the growth of A. gallica. Moreover, we identified a total of 2071 differentially expressed genes (DEGs) by analyzing the transcriptome sequencing data of A. gallica at 5 and 10 hour of NAA treatment. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that these unigenes were significantly enriched in the metabolism pathways of arginine, proline, propanoate, phenylalanine and tryptophan. The expression levels of the general amino acid permease (Gap), ammonium transporter (AMT), glutamate dehydrogenase (GDH), glutamine synthetase (GS), Zn(II) 2Cys6 and C2H2 transcription factor genes were upregulated. Our transcriptome analysis showed that the amino acid and nitrogen metabolism pathways in Armillaria were rapidly induced within hours after NAA treatment. These results provide valuable insights into the molecular mechanisms by which NAA promotes the growth of Armillaria species.

Pseudomonas fluorescens BsEB-1: an endophytic bacterium isolated from the root of Bletilla striata that can promote its growth.

An endophytic Pseudomonas fluorescens (BsEB-1) was obtained from the roots of Bletilla striata. We investigated its growth-promoting properties and observed the impact of its inoculation on both the growth and polysaccharide content of Bletilla striata tubers. It was found that BsEB-1 possessed three growth-promoting activities: phosphate-solubilizing, produced indoleacetic acid (IAA) and siderophores, but had no nitrogen-fixing activity. BsEB-1 could rapidly attach to the root hairs of Bletilla striata tissue culture seedlings and endophytically colonize the region of maturation in the roots. It also significantly promoted the rooting and transplant survival rate of the seedlings, as well as the growth and expansion of the tubers, but did not increase their polysaccharide content. Pseudomonas fluorescens BsEB-1 exhibits potential for applications in the artificial planting of Bletilla striata.

Overexpression of tomato thioredoxin h (SlTrxh) enhances excess nitrate stress tolerance in transgenic tobacco interacting with SlPrx protein.

The thioredoxin (Trx) system plays a vital function in cellular antioxidative defense. However, little is known about Trx in tomato under excess nitrate. In this study, we isolated the tomato gene encoding h-type Trx gene (SlTrxh). The mRNA transcript of SlTrxh in roots and leaves of tomato was induced incrementally under excess nitrate for 24 h. Subcellular localization showed that SlTrxh might localize in the cytoplasm, nucleus and plasma membrane. Enzymatic activity characterization revealed that SlTrxh protein possesses the disulfide reductase function and Cysteine (Cys) 54 is important for its activity. Overexpressing SlTrxh in tobacco resulted in increasing seed germination rate, root length and decreasing H2O2 and O2- accumulation, compared with the wild type (WT) tobacco under nitrate stress. While overexpressing SlTrxhC54S (Cysteine 54 mutated to Serine) in tobacco showed decreased germination rate and root length compared with the WT after nitrate treatment. After nitrate stress treatment, SlTrxh overexpressing transgenic tobacco plants have lower malonaldehyde (MDA), H2O2 contents and Reactive Oxygen Species (ROS) accumulation, and higher mRNA transcript level of NtP5CS, NtDREB2, higher ratio of ASA/DHA and GSH/GSSG, higher activities of ascorbate peroxidase and NADP thioredoxin reductase. Besides, SlTrxh overexpressing plants showed higher tolerance to Methyl Viologen (MV) in the seed germination and seedling stage. The yeast two-hybrid, pull-down, Co-immunoprecipitation and Bimolecular luciferase complementation assay confirmed that SlTrxh physically interacted with tomato peroxiredoxin (SlPrx). These results suggest that SlTrxh contributes to maintaining ROS homeostasis under excess nitrate stress interacting with SlPrx and Cys54 is important for its enzyme activity.

The interaction of MYB, bHLH and WD40 transcription factors in red pear (Pyrus pyrifolia) peel.

KEY MESSAGE: Sunlight enhanced peel color and significantly up-regulated the expression of PyMYB10 and PybHLH genes. MYB-bHLH-WD40 transcriptional complex forms in the light and is involved in regulating anthocyanin accumulation in the peel. Anthocyanin is the major pigment in the peel of Yunnan red pear (Pyrus pyrifolia (Burm.) Nak.). A transcriptional activation protein complex, involving members of the transcription factor classes of MYB, bHLH and WD40, regulates anthocyanin biosynthesis. This complex was examined in the peel of red pear. In order to clarify the interaction of PyMYB10, PybHLH and PyWD40, fruit were bagged then peel samples collected 0, 3, 5, and 7 days after bag removal. Samples were used for Western blotting and protein interaction analysis. The results showed that sunlight enhanced peel color and significantly up-regulated the expression of both PyMYB10 and PybHLH genes. Co-immunoprecipitation (Co-IP) analysis showed that PybHLH interacted with PyMYB10 or PyWD40, and PyMYB10 interacted with PyWD40. Using onion cells as a model system, bimolecular fluorescence complementation (BiFC) confirmed these interactions and showed that the interaction localized to the nuclei. GST Pull down and Far-Western blotting assays demonstrated that PybHLH interacted with PyMYB10 or PyWD40, respectively, and PyMYB10 interacted with PyWD40 in vitro. In addition, EMSA assay showed that PyMYB10 can directly bind to the promoter of the gene encoding the anthocyanin biosynthesis enzyme anthocyanidin synthase (PyANS). Taken together, these results showed that the ternary complex of PyMYB10, PybHLH and PyWD40 transcription factors forms to regulate anthocyanin biosynthesis and accumulation in Yunnan red pear.

Co-overexpression of AtSHMT1 and AtFDH induces sugar synthesis and enhances the role of original pathways during formaldehyde metabolism in tobacco.

Serine hydroxymethyltransferase 1 (SHMT1) is a key enzyme in the photorespiration pathway in higher plants. Our previous study showed that AtSHMT1 controls the assimilation of HCHO to sugars in Arabidopsis. The expression of SHMT1 was induced in Arabidopsis but was inhibited in tobacco under HCHO stress. To investigate whether the function of AtSHMT1 in the HCHO assimilation could be exerted in tobacco, AtSHMT1 was overexpressed alone (S5) or co-overexpressed (SF6) with Arabidopsis formate dehydrogenase (AtFDH) in leaves using a light-inducible promoter in this study. 13C NMR analyses showed that the 13C-metabolic flux from H13CHO was introduced to sugar synthesis in SF6 leaves but not in S5 leaves. The increase in the production of metabolites via the original pathways was particularly greater in SF6 leaves than in S5 leaves, suggesting that co-overexpression of AtSHMT1 and AtFDH is more effective than overexpression of AtSHMT1 alone in the enhancement of HCHO metabolism in tobacco leaves. Consequently, the increase in HCHO uptake and resistance was greater in SF6 leaves than in S5 leaves. The mechanism underlying the role of overexpressed AtSHMT1 and AtFDH was discussed based on changes in photosynthetic parameters, chlorophyll content, antioxidant enzyme activity and the oxidative level in leaves.

De novo RNA sequencing and analysis reveal the putative genes involved in diterpenoid biosynthesis in Aconitum vilmorinianum roots.

In this study, the putative genes involved in diterpenoid alkaloids biosynthesis in A. vilmorinianum roots were revealed by transcriptome sequencing. 59.39 GB of clean bases and 119,660 unigenes were assembled, of which 69,978 unigenes (58.48%) were annotated. We identified 27 classes of genes (139 candidate genes) involved in the synthesis of diterpenoid alkaloids, including the mevalonate (MVA) pathway, the methylerythritol 4-phosphate (MEP) pathway, the farnesyl diphosphate regulatory pathway, and the diterpenoid scaffold synthetic pathway. 12 CYP450 genes were identified. We found that hydroxymethylglutaryl-CoA reductase was the key enzyme in MVA metabolism, which was regulated by miR6300. Transcription factors, such as bHLH, AP2/EREBP, and MYB, used to synthesize the diterpenes were analyzed. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02646-6.

Measuring the expression and activity of the CAT enzyme to determine Al resistance in soybean.

To elucidate the mechanism of soybean resistance to Al, physiological and biochemical indices and antioxidant enzyme expression and activities were systematically analyzed in Al-sensitive (Glycine max Merr., Yunnan Province of China, SB) and Al-resistant Dambo (Glycine max Merr., Kyoto of Japan, RB) black soybean plants. According to the results, the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in RB root tips were significantly lower than those in SB root tips, though the opposite results occurred for soluble protein contents. Moreover, the expression and activities of superoxide dismutase (SOD, EC1.15.1.1.1.1.1.1), peroxidase (POD, EC1.11.1.7) and catalase (CAT, EC1.11.1.6) under 0-400 µM Al for 0-96 h were greater in RB than in SB. However, below 100 µM Al, the activities of those enzymes in SB increased with increasing Al concentration and treatment duration, with SOD activity being lowest and CAT activity exceeding that of POD with increasing Al concentration. Overall, enzyme activity in SB treated with Al at concentrations greater than 200 µM was lower than that in the SB control (CK; not treated with Al) and decreased with treatment duration. Additionally, at Al concentrations lower than 200 µM, enzyme activities in RB were significantly greater than those in RB CK and increased with both Al concentration and treatment duration. Moreover, enzyme activity in RB treated with 400 µM Al was slightly greater than that in RB CK. Thus, CAT activity determines soybean resistance to Al. These results indicate that soybean resistance to Al can be enhanced by regulating the expression and activity of antioxidant enzymes to remove H2O2 under Al stress.

Hydrogen sulfide alleviates oxidative damage under excess nitrate stress through MAPK/NO signaling in cucumber.

Hydrogen sulfide (H2S) is emerging as a potential messenger molecule involved in modulation of physiological processes in plants. Mitogen-activated protein kinase (MAPK) and nitric oxide (NO) are essential for abiotic stress signaling. This work investigated the effects of H2S and the crosstalk between H2S, MAPK and NO in cucumber roots under nitrate stress. The inhibitory effect of 140 mM nitrate on the growth of shoot and root was substantially alleviated by treatment with H2S donor sodium hydrosulfide (NaHS), especially 100 µM NaHS. Treatment with 100 µM NaHS reduced malondialdehyde (MDA) and H2O2 contents, ROS accumulation and increased the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX). CsNMAPK transcript level was up-regulated by NaHS treatment, while significantly decreased by propargylglycine (PAG, specific inhibitor of H2S biosynthesis) and hypotaurine (HT, H2S scavenger) in cucumber roots under nitrate stress. NO accumulation was increased by NaHS treatment under nitrate stress, but reduced by HT, PAG and PD98059, indicating that NO might function downstream of MAPK and H2S. MAPK inhibitor PD98059 and NO scavenger (cPTIO) reversed the alleviating effect of H2S by increasing MDA and H2O2 contents, and decreasing antioxidant enzyme activities of SOD, CAT, POD, APX, and the endogenous H2S contents and LCD activities under nitrate stress. In conclusion, H2S played a protective role in cucumber seedlings under nitrate stress and MAPK/NO signaling were involved in the process by regulating antioxidant enzyme activities.

A small proportion of litter-derived nitrogen is assimilated by plant biomass or immobilized in sediments regardless of harvest management as detected by 15N-labeled Phragmites litter in a constructed wetland.

Emergent aquatic macrophytes play an important role in the removal of nutrients in constructed wetlands (CWs). However, plant biomass supplies litter after the onset of senescence. Although litter-derived nitrogen (N) has been considered a nutrient source for the internal loading that may reduce CW performance, little is known about the quantitative N dynamics associated with litter decomposition. Thus, a controversial question remains about whether plant harvest is needed to manage CWs. In this study, we evaluated the decomposition and the fate of N derived from 15N-labeled Phragmites litter in a CW for 1 year. To simulate respective natural conditions, two treatments, including (1) a single winter harvest and (2) no harvest where the latter supplies a greater stem litterfall, were compared. Although the dry weight of the added stem litter was approximately 4.7 times larger in the no harvest plot than in the harvest plot, the total N content of the initial 15N-labeled litter was only 1.2 times higher in the no harvest plot than in the harvest plots because of the low N concentration in the stem litter. The litter functioned as a minor N sink within the first 6 months of decomposition, and it then shifted to functioning as a minor N source after 1 year of decomposition. The recovery of litter-derived N in the sediment and plant biomass was low (less than 10% of the initial litter N), and much of the remaining N might have been released into ambient water or lost through denitrification. Furthermore, our results suggested a potentially low contribution of litter-derived N to internal N loading for at least 1 year regardless of the harvest management treatment.