Research Progress on Active Ingredients and Product Development of Lycium ruthenicum Murray.

Lycium ruthenicum Murray possesses significant applications in both food and medicine, including antioxidative, anti-tumor, anti-fatigue, anti-inflammatory, and various other effects. Consequently, there has been a surge in research endeavors dedicated to exploring its potential benefits, necessitating the organization and synthesis of these findings. This article systematically reviews the extraction and content determination methods of active substances such as polysaccharides, anthocyanins, flavonoids, and polyphenols in LRM in the past five years, as well as some active ingredient composition determination methods, biological activities, and product development. This review is divided into three main parts: extraction and determination methods, their bioactivity, and product development. Building upon prior research, we also delve into the economic and medicinal value of Lycium ruthenicum Murray, thereby contributing significantly to its further exploration and development. It is anticipated that this comprehensive review will serve as a valuable resource for advancing research on Lycium ruthenicum Murray.

Observational Insights into Isoprene Secondary Organic Aerosol Formation through the Epoxide Pathway at Three Urban Sites from Northern to Southern China.

Isoprene is the most abundant precursor of global secondary organic aerosol (SOA). The epoxide pathway plays a critical role in isoprene SOA (iSOA) formation, in which isoprene epoxydiols (IEPOX) and/or hydroxymethyl-methyl-α-lactone (HMML) can react with nucleophilic sulfate and water producing isoprene-derived organosulfates (iOSs) and oxygen-containing tracers (iOTs), respectively. This process is complicated and highly influenced by anthropogenic emissions, especially in the polluted urban atmospheres. In this study, we took a 1-year measurement of the paired iOSs and iOTs formed through the IEPOX and HMML pathways at the three urban sites from northern to southern China. The annual average concentrations of iSOA products at the three sites ranged from 14.6 to 36.5 ng m-3. We found that the nucleophilic-addition reaction of isoprene epoxides with water dominated over that with sulfate in the polluted urban air. A simple set of reaction rate constant could not fully describe iOS and iOT formation everywhere. We also found that the IEPOX pathway was dominant over the HMML pathway over urban regions. Using the kinetic data of IEPOX to estimate the reaction parameters of HMML will cause significant underestimation in the importance of HMML pathway. All these findings provide insights into iSOA formation over polluted areas.

Evidence for nitrite-dependent anaerobic methane oxidation as a previously overlooked microbial methane sink in wetlands.

The process of nitrite-dependent anaerobic methane oxidation (n-damo) was recently discovered and shown to be mediated by "Candidatus Methylomirabilis oxyfera" (M. oxyfera). Here, evidence for n-damo in three different freshwater wetlands located in southeastern China was obtained using stable isotope measurements, quantitative PCR assays, and 16S rRNA and particulate methane monooxygenase gene clone library analyses. Stable isotope experiments confirmed the occurrence of n-damo in the examined wetlands, and the potential n-damo rates ranged from 0.31 to 5.43 nmol CO2 per gram of dry soil per day at different depths of soil cores. A combined analysis of 16S rRNA and particulate methane monooxygenase genes demonstrated that M. oxyfera-like bacteria were mainly present in the deep soil with a maximum abundance of 3.2 × 10(7) gene copies per gram of dry soil. It is estimated that ∼0.51 g of CH4 m(-2) per year could be linked to the n-damo process in the examined wetlands based on the measured potential n-damo rates. This study presents previously unidentified confirmation that the n-damo process is a previously overlooked microbial methane sink in wetlands, and n-damo has the potential to be a globally important methane sink due to increasing nitrogen pollution.

Vertical distribution of nitrite-dependent anaerobic methane-oxidising bacteria in natural freshwater wetland soils.

Nitrite-dependent anaerobic methane oxidation (n-damo) is a recently discovered process that is catalysed by "Candidatus Methylomirabilis oxyfera". In the present study, the vertical distribution (0-10, 20-30, 50-60 and 90-100 cm) of M. oxyfera-like bacteria was investigated in Xiazhuhu wetland, the largest natural wetland on the southern Yangtze River (China). Phylogenetic analyses showed that group A of M. oxyfera-like bacteria and pmoA genes occurred primarily at depths of 50-60 and 90-100 cm. Quantitative PCR further confirmed the presence of M. oxyfera-like bacteria in soil cores from different depths, with the highest abundance of 5.1 × 10(7) copies g(-1) dry soil at depth of 50-60 cm. Stable isotope experiments demonstrated that the n-damo process occurred primarily at depths of 50-60 and 90-100 cm, with the potential rates ranging from 0.2 to 14.5 nmol CO2 g(-1) dry soil d(-1). It was estimated that the methane flux may increase by approximately 2.7-4.3% in the examined wetland in the absence of n-damo. This study shows that the deep wetland soils (50-60 and 90-100 cm) are the preferred habitats for M. oxyfera-like bacteria. The study also highlights the potential importance of these bacteria in the methane and nitrogen cycles in deep wetland soils.

Evidence for the cooccurrence of nitrite-dependent anaerobic ammonium and methane oxidation processes in a flooded paddy field.

Anaerobic ammonium oxidation (anammox) and nitrite-dependent anaerobic methane oxidation (n-damo) are two of the most recent discoveries in the microbial nitrogen cycle. In the present study, we provide direct evidence for the cooccurrence of the anammox and n-damo processes in a flooded paddy field in southeastern China. Stable isotope experiments showed that the potential anammox rates ranged from 5.6 to 22.7 nmol N2 g(-1) (dry weight) day(-1) and the potential n-damo rates varied from 0.2 to 2.1 nmol CO2 g(-1) (dry weight) day(-1) in different layers of soil cores. Quantitative PCR showed that the abundance of anammox bacteria ranged from 1.0 × 10(5) to 2.0 × 10(6) copies g(-1) (dry weight) in different layers of soil cores and the abundance of n-damo bacteria varied from 3.8 × 10(5) to 6.1 × 10(6) copies g(-1) (dry weight). Phylogenetic analyses of the recovered 16S rRNA gene sequences showed that anammox bacteria affiliated with "Candidatus Brocadia" and "Candidatus Kuenenia" and n-damo bacteria related to "Candidatus Methylomirabilis oxyfera" were present in the soil cores. It is estimated that a total loss of 50.7 g N m(-2) per year could be linked to the anammox process, which is at intermediate levels for the nitrogen flux ranges of aerobic ammonium oxidation and denitrification reported in wetland soils. In addition, it is estimated that a total of 0.14 g CH4 m(-2) per year could be oxidized via the n-damo process, while this rate is at the lower end of the aerobic methane oxidation rates reported in wetland soils.

Characterization of acute renal allograft rejection by proteomic analysis of renal tissue in rat.

Rapid and reliable biomarkers of renal allograft rejection have not been available. This study aimed to investigate biomarkers in renal allograft tissue using proteomic analysis. Orthotopic kidney transplantations were performed using Fisher (F344) or Lewis rats as donors and Lewis rats as recipients. Syngenic control group (Group I) constituted F344-to-F344 orthotopic kidney allo-transplantations (n = 8); and allogenic group (Group II) consisted of F344-to-Lewis orthotopic kidney allo-transplantations (n = 8). Renal tissues were harvested 7 days after transplantation. Samples were analyzed using 2-D electrophoresis and matrix assisted laser desorption ionization-time of flight mass spectrometry. 6 differentially expressed proteins were identified between allogenic group and syngenic control group. A rat model of acute renal allograft rejection was successfully set up. Differentially expressed proteins in renal allograft tissue of rat were detected using proteomic analysis and might serve as novel diagnostic and therapeutic targets in human. Quantitative proteomics, using MALDL-TOF-MS methodology has the potential to provide a profiling and a deeper understanding of acute renal rejection.

[The dose response decrease of lung function associated with the urinary polycyclic aromatic hydrocarbons metabolites in coke oven workers].

OBJECTIVE: To analyze the relationship between metabolites of polycyclic aromatic hydrocarbons (PAHs) and lung function in coke oven workers, and to provide scientific basis for further exploring the potential mechanism and developing the preventing strategies of the workers' early lung damage. METHODS: We measured carbon monoxide, sulfur dioxide, benzene soluble matter, particulate matters, and PAHs at different workplaces of a coke oven plant. Detailed information on demography and occupational health condition of 912 workers were collected. We divided these workers into control group and coke oven group according to their workplaces and the different concentrations of COEs in the environment. We detected 10 urinary PAH metabolites and lung function using gas chromatography-mass spectrometry and spirometric tests, respectively. RESULTS: FEV(1.0) (91.12 ± 13.31) and FEV(1.0)/FVC (108.61 ± 20.37) of the coke oven group is significantly lower than the control group (94.16 ± 15.57, 113.45 ± 19.70). In the coke oven group, the hydroxyphenanthrene and 1-hydroxypyrene are negatively correlated with FEV(1.0)/FVC (ß = -0.136, ß = -0.100), Ptrend < 0.05 for all. CONCLUSION: The dose response decrease of lung function is associated with the urinary PAH metabolites in coke oven workers. Indicated that the long exposure to PAHs may cause the early lung damage in coke oven workers, phenanthrene and pyrene may be the main factors.

[Characteristics of particulate matter pollution in coke oven plant].

OBJECTIVE: To explore the characteristics of particulate matter pollution in coke oven plant, so as to provide scientific data for establishing occupational exposure limits for coke oven emissions. METHODS: Concentrations of CO, SO2, BSM, BTEX (concentrations of benzene, toluene and xylene were determined in this study), PM10, PM2.5, 16 selected PAHs in PM10 and PM2.5 were determined in the work environment of a coke oven plant in Wuhan. The work environment was divided into the adjunct area, the bottom of, the side of and the top of coke oven. RESULTS: The concentrations of CO, SO2, BSM, BETX, PM10, PM2.5, PAHs in PM10 and PM2.5 were significantly related to working environmental categories, respectively, and were increasing as the adjunct area < bottom < side < top (P (trend) < 0.05). PM10 was statistically significantly correlated with CO, SO2, benzene, BTEX and BSM (0.705, 0.823, 0.664, 0.624 and 0.734, respectively). PM2.5 was statistically significantly correlated with CO, SO2, benzene, BTEX and BSM (0.635, 0.916, 0. 680, 0.553 and 0.726, respectively). BSM was statistically significantly correlated with benzene (0.689). The ratios of PM2.5 to PM10 between different work environments were not significantly different in one-way ANOVA (P > 0.05). The distribution of aromatic rings and the concentrations of total benzo[a] pyrene equivalents in PM10 and PM2.5 were not statistically different between work environments. CONCLUSION: The concentrations of particulate matter was related with other contents of coke oven emissions in coke work environment, and the contents and types of PAHs in PM10 and PM2.5 were similar.

[Effects of smoking on the concentrations of urinary 10 metabolites of polycyclic aromatic hydrocarbons in coke oven workers].

OBJECTIVE: To explore the effects of smoking on urinary 10 metabolites of polycyclic aromatic hydrocarbons (PAHs) in the coke oven workers. METHODS: Occupational health examination was performed on 1401 coke oven workers in one coking plant, their urine were collected respectively. The concentrations of the ten monohydroxy polycyclic aromatic hydrocarbons in urine were detected by gas chromatography/mass spectrometry. The 1401 workers were divided into four groups, namely control, adjunct workplaces, bottom and side, top group according to their workplaces and the different concentrations of PAHs in the environment. The concentrations of the ten monohydroxy polycyclic aromatic hydrocarbons between smokers and nonsmokers in each workplace group were compared using analysis of covariance, respectively. RESULTS: The levels of concentrations of the sixteen polycyclic aromatic hydrocarbons we detected at control were significantly higher than those at other areas (P < 0.05). Comparing the ten monohydroxy polycyclic aromatic hydrocarbons levels between smokers and nonsmokers, the levels of 1-hydroxynaphthalene and 2-hydroxynaphthalene among smokers were higher than nonsmokers with statistically significance in control, adjunct workplaces, bottom and side and top groups (P < 0.05). However, the levels of 1-hydroxypyrene had no statistically significant differences between the four areas. CONCLUSION: Urinary 1-hydroxynaphthalene and 2-hydroxynaphthalene may be used as biomarkers for the impact of smoking on monohydroxy polycyclic aromatic hydrocarbons in the coke oven workers.

The DeltaN p63 Promotes EMT and Metastasis in Bladder Cancer by the PTEN/AKT Signalling Pathway.

Bladder cancer is a common tumour of the urinary system, and more than 90% is urothelial carcinoma. Therefore, it is important for discovering the key target genes and molecules of bladder tumour cell metastasis and invasion. Our research initially explored the regulation of deltaN p63 on the progression and metastasis of bladder cancer and found that deltaN p63 can influence the occurrence of EMT through PTEN and ultimately regulate the growth and metastasis of bladder cancer. In summary, this study identified a new EMT regulator, deltaN p63, further revealed the mechanism of the invasion and metastasis of bladder cancer cells, and provided a theoretical basis for finding new target molecules and drugs to treat bladder cancer. In conclusion, this study will further reveal the mechanism of tumour cell invasion and metastasis and provide a theoretical basis for cancer treatment to find new target molecules and drugs.

[Construction of deltaNp63 specific small hairpin RNA expressing plasmid and its role in bladder cancer--a preliminary study].

OBJECTIVE: To construct deltaNp63 specific small hairpin RNA (shRNA) expressing plasmid,to examine its inhibitory effect to the expression of deltaNp63 protein and mRNA in transitional cell carcinoma of the bladder (TCCB) , its effect on TCCB cells cycle and proliferation. METHODS: DeltaNp63 specific oligonucleotides were designed and synthesized. These oligonucleotides were annealed to form double strand DNA fragments and this fragment was cloned into Pgenesil-1 plasmid. The recombinant deltaNp63-shRNA expression construct was confirmed by using Pst I + Sal I double digestion and by sequencing. Fluorescence staining was used to confirm the success of transfection in TCCB cells under the fluorescence microscope. The inhibitory effect of deltaNp63-shRNA construct was examined with semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemical staining assay. The cell cycle of TCCB cells was assayed by flow cytometry (FCM). The cellular proliferation of TCCB cells was assayed by tetrazolium bromide (MTT) colorimetry. RESULTS: The deltaNp63-shRNA expression plasmid was successfully constructed and transfected into TCCB cells. It can effectively reduce the expression of deltaNp63 protein and mRNA. The reduction rate of deltaNp63 mRNA was 63.0%, and the G0/G1 ratio was increased and S phase was decreased in transfected TCCB cells. The cellular proliferation was also lower in transfected 5637 cells in comparrison with that of non-transfected TCCB cells. CONCLUSION: A deltaNp63-shRNA expression plasmid, constructed from Pgenesil-1 plasmid, can successfully be transfected into TCCB cells and can effectively inhibit the expression of deltaNp63 protein and mRNA. It also can take part in regulation of the cell cycling and inhibit the cellular proliferation of TCCB cells.

[Effect of saffor (Carthamus tinctorius) injection on renal ischemia/reperfusion injury in rats].

OBJECTIVE: To study the effect and mechanism of saffor injection on renal ischemia/reperfusion (I/R) injury in rats. METHOD: Seventy-five SD rats were randomly divided into five groups (n = 15, in each), normal control groups, I/R control groups, low-dose treatment groups, middle-dose treatment groups and high-dose treatment groups. After rat's I/R injury model was established, renal function was assessed by measuring serum creatinine, blood urea nitrogen, urine osmotic pressure and urine osmotic pressure/blood osmotic pressure, the apoptosis rate in I/R renal tissure was measured by TUNEL method and caspase-3 concentration was measured by immunohistochemistry. RESULT: Reperfusion of the ischemic kidney induced marked renal dysfunction. Saffor injection significantly inhibited the reperfusion-associated increase in apoptosis rate and caspase-3 protein absorbance value. Moreover, the renal dysfunction at all treatment groups was markedly ameliorated by Saffor injection. (P < 0.01). CONCLUSION: The results show that saffor injection significantly reduces the renal dysfunction and injury caused by I/R of the kidney, And the protective effect of Saffor injection may be related to the inhibition of cell apoptosis and caspase-3 gene expression following renal I/R.

Lead contamination in tea garden soils and factors affecting its bioavailability.

The consumption of heavy metals is detrimental to human health and most countries restrict the concentration of metals such as lead (Pb) in food and beverages. Recent tests have detected high Pb concentrations in certain commercial brands of tea leaves and this finding has raised concerns for both producers and consumers. To investigate what factors may be contributing to the increase in Pb accumulation in the tea leaves we collected tea leaves and soils from tea producing areas and analyzed them for Pb concentration, pH and organic matter content. The result showed the Pb concentration of 47% investigated tea leaves samples was beyond 2 mg kg(-1), the permissible levels given by China. The total Pb concentration in the surface and subsurface soil layers averaged 36.4 and 32.2 mg kg(-1), respectively which fall below of the 60 mg kg(-1) limit provided for organic tea gardens in China. The pH of the tea garden soils was severely acidic with the lowest pH of 3.37. Soils under older tea gardens tended to have a lower pH and a higher Pb bioavailability which was defined as the amount of lead extracted by CaCl2 solution than those under younger tea gardens. We found that the concentration of bioavailable Pb and the percentage of bioavailable Pb (bioavailable Pb relative to total Pb concentration) were positively correlated with soil H+ activity and soil organic matter content, and the organic matter accumulation contribute more effects on Pb bioavailability in these two factors. We conclude that soil acidification and organic matter accumulation could contribute to increasing Pb bioavailability in soil and that these could increase Pb uptake and accumulation in the tea leaves.

Lead contamination in tea leaves and non-edaphic factors affecting it.

Recent tests have detected high lead (Pb) concentrations in some commercial brands of tea leaves and this finding has raised concerns due to the possible health-related problems associated with Pb poisoning. In present research, we investigated the Pb contamination in tea leaves produced in Zhejiang province in China. Pb concentrations in all tea leaves sampled were below 5 mg/kg, the permissible levels given by Chinese Ministry of Agriculture, indicating that Pb contamination in this province is not excessive. We then investigated the non-edaphic factors that may potentially contribute to Pb accumulation in tea leaves. Pb concentration in tea leaves was found to be positively correlated with the industrialization level of a district (R = 0.83, the significant level at P < 0.05), and greater amounts of Pb were washed from the leaves of plants in districts with more industrial activity. This suggests that Pb accumulation in tea leaves could, in part, be attributed to industrial activity through the precipitation of atmospheric Pb. Furthermore greater amounts of Pb were washed from the leaves of plants growing near road than those growing farther away from road. This trend indicates that automobile activity was another likely contributor to Pb accumulation in tea. Pb content of green tea was also affected by the processing of the leaves in the factory. In particular the twisting and water-removal stages caused increases in Pb content in the tea product. This study suggests that non-edaphic factors also contribute to the Pb accumulation in tea.

Upregulation of cell adhesion through delta Np63 silencing in human 5637 bladder cancer cells.

Some researchs have demonstrated that the loss of delta Np63 is associated with aggressive phenotypes and poor prognosis. However, other research indicates that delta Np63 is considered to have oncogenic properties. Delta Np63 overexpression is often observed in association with the oncogenic growth of squamous cell carcinomas and bladder cancer. In this study, we investigated the oncogenic role of delta Np63 in regulating cell adhesion in transitional cell carcinoma of the bladder (TCCB). The cells were stably transfected with the delta Np63 short hairpin RNA (shRNA) plasmid. Immunocytochemistry was performed to determine the knockdown efficiency. Tumour cells were studied for their ability to adhere to vascular endothelial cells. Confocal microscopy was used to analyse the changes in cytoskeletal F-actin. F-actin expression was measured by flow cytometry. Cell invasion ability was assessed using transwell chambers. The delta Np63-silenced tumour cells were shown to adhere more tightly than controls to vascular endothelial cells (P<0.05). The content of F-actin in the delta Np63-silenced cells was enhanced (P<0.05). The Matrigel invasion assays showed that human 5637 bladder cancer cells had a lower degree of motility when transfected with pdelta Np63-shRNA (P<0.05). In conclusion, silencing of the delta Np63 expression can enhance the adhesiveness of 5637 cells by inducing F-actin cytoskeleton production, and it will possibly inhibit the TCCB invasion and metastasis.

Iron deficiency-induced secretion of phenolics facilitates the reutilization of root apoplastic iron in red clover.

Phenolic compounds are frequently reported to be the main components of root exudates in response to iron (Fe) deficiency in Strategy I plants, but relatively little is known about their function. Here, we show that removal of secreted phenolics from the root-bathing solution almost completely inhibited the reutilization of apoplastic Fe in roots of red clover (Trifolium pratense). This resulted in much lower levels of shoot Fe and significantly higher root Fe compared with control and also resulted in leaf chlorosis, suggesting this approach stimulated Fe deficiency. This was supported by the observation that phenolic removal significantly enhanced root ferric chelate reductase activity, which is normally induced by plant Fe deficiency. Furthermore, root proton extrusion, which also is normally increased during Fe deficiency, was found to be higher in plants exposed to the phenolic removal treatment too. These results indicate that Fe deficiency-induced phenolics secretion plays an important role in the reutilization of root apoplastic Fe, and this reutilization is not mediated by proton extrusion or the root ferric chelate reductase. In vitro studies with extracted root cell walls further demonstrate that excreted phenolics efficiently desorbed a significant amount of Fe from cell walls, indicating a direct involvement of phenolics in Fe remobilization. All of these results constitute the first direct experimental evidence, to our knowledge, that Fe deficiency-induced secretion of phenolics by the roots of a dicot species improves plant Fe nutrition by enhancing reutilization of apoplastic Fe, thereby improving Fe nutrition in the shoot.

Mechanisms of microbially enhanced Fe acquisition in red clover (Trifolium pratense L.).

Soil microorganisms may play an important role in plant Fe uptake from soils with low Fe bioavailability, but there is little direct experimental evidence to date. We grew red clover, an Fe-efficient leguminous plant, in a calcareous soil to investigate the role of soil microbial activity in plant Fe uptake. Compared with plants grown in non-sterlie (NS) grown plants, growth and Fe content of the sterile(s) grown plants was significantly inhibited, but was improved by foliar application of Fe EDTA, indicating that soil microbial activity should play an important role in plant Fe acquisition. When soil solution was incubated with phenolic root exudates from Fe-deficient red clover, a few microbial species thrived while growth of the rest was inhibited, suggesting that the Fe-deficient (-Fe) root exudates selectively influenced the rhizosphere's microbial community. Eighty six per cent of the phenolic-tolerant microbes could produce siderophore [the Fe(III) chelator] under -Fe conditions, and 71% could secrete auxin-like compounds. Interestingly, the synthetic and microbial auxins (MAs) significantly enhanced the Ferric reduction system, suggesting that MAs, in addition to siderophores, are important to plant Fe uptake. Finally, plant growth and Fe uptake in sterilized soil were significantly increased by rhizobia inoculation. Root Fe-EDTA reductase activity in the -Fe plant was significantly enhanced by rhizobia infection, and the rhizobia could produce auxin but not siderophore under Fe-limiting conditions, suggesting that the contribution of nodulating rhizobia to plant Fe uptake can be at least partially attributed to stimulation of turbo reductase activity through nodule formation and auxin production in the rhizosphere. Based on these observations, we propose as a model that root exudates from -Fe plants selectively influence the rhizosphere microbial community, and the microbes in turn favour plant Fe acquisition by producing siderophores and auxins.

Comparative studies on the effect of a protein-synthesis inhibitor on aluminium-induced secretion of organic acids from Fagopyrum esculentum Moench and Cassia tora L. roots.

Aluminium (Al)-induced secretion of organic acids from plant roots is considered a mechanism of Al resistance, but the processes leading to the secretion of organic acids are still unknown. In the present study, a protein-synthesis inhibitor, cycloheximide (CHM), was used to investigate its effect on Al-induced organic acid secretion in a pattern I (rapid exudation of organic acids under Al stress) plant buckwheat (Fagopyrum esculentum Moench) and a pattern II (exudation of organic acids was delayed by several hours under Al stress) plant Cassia tora L. A dose-response experiment showed that the secretion of oxalate by buckwheat roots was not affected by CHM when added in the range from 0 to 50 microM, with or without exposure to 100 microm Al, but the secretion of citrate was completely inhibited by 30 microM CHM in C. tora. A time-course experiment showed that even prolonged exposure to 20 microM CHM did not affect oxalate secretion in buckwheat, but significantly inhibited citrate secretion in C. tora. However, citrate synthase (CS) activity in C. tora was not affected during 12 h exposure to 100 microM Al when compared with that in control roots, although CHM can inhibit CS activity effectively. These results indicated that CS activity was not related to Al-regulated citrate efflux in C. tora. The total protein was decreased by 14.0% and 32.3% in C. tora and buckwheat root tip, respectively, after 3-h treatment with 20 microM CHM. A 3-h pulse with 20 microM CHM completely inhibited citrate efflux in C. tora during the next 6-h exposure to Al, although a small amount of citrate was exuded after 9-h exposure. However, oxalate efflux in buckwheat was not influenced by a similar treatment. In buckwheat, a 3-h pulse with 100 microM Al maintained oxalate secretion at a high level during the next 9 h, with or without CHM treatment. Conversely, in C. tora a 6-h pulse with 100 microM Al induced significant secretion of citrate which was inhibited by the CHM. Taken together, these findings suggest that both de novo synthesis and activation of an anion channel are needed for Al-induced secretion of citrate in C. tora, but in buckwheat the plasma membrane protein responsible for oxalate secretion pre-exists.

Aluminium resistance requires resistance to acid stress: a case study with spinach that exudes oxalate rapidly when exposed to Al stress.

Spinach is a vegetable with a high oxalate concentration in its tissues. Oxalate efflux from spinach (Spinacia oleracea L. cv. Quanneng) roots was rapidly stimulated (within 30 min) by aluminium (Al) treatment. The efflux was constant within 6 h, but increased with increasing Al concentration. The efflux was confined to the root tip (0-5 mm), which showed a 5-fold greater efflux than the root zone distal to the tip (5-10 mm). Oxalate efflux could not be triggered by treatment with the trivalent cation lanthanum or by phosphorus deficiency, indicating that the efflux was specific to the Al treatment. All this evidence suggested that spinach possesses Al-resistance mechanisms. However, spinach was found to be as sensitive to Al toxicity as the Al-sensitive wheat line ES8, which had no Al-dependent organic acids efflux. The Al accumulated in the apical 5 mm of the roots of spinach which was also similar to that in the Al-sensitive wheat after 24 h treatment with 50 microM AlCl(3), indicating a non-exclusion mechanism. In addition, root elongation in spinach was significantly inhibited at pH 4.5, compared with that at pH 6.5. Based on this evidence, it is concluded that the sensitivity to acid stress in spinach could mask the potential role for oxalate to protect the plant roots from Al toxicity.

Immobilization of aluminum with phosphorus in roots is associated with high aluminum resistance in buckwheat.

Oxalic acid secretion from roots is considered to be an important mechanism for aluminum (Al) resistance in buckwheat (Fygopyrum esculentum Moench). Nonetheless, only a single Al-resistant buckwheat cultivar was used to investigate the significance of oxalic acid in detoxifying Al. In this study, we investigated two buckwheat cultivars, Jiangxi (Al resistant) and Shanxi (Al sensitive), which showed significant variation in their resistance to Al stress. In the presence of 0 to 100 microM Al, the inhibition of root elongation was greater in Shanxi than that in Jiangxi, and the Al content of root apices (0-10 mm) was much lower in Jiangxi. However, the dependence of oxalic acid secretion on external Al concentration and the time course for secretion were similar in both cultivars. Furthermore, the variation in Al-induced oxalic acid efflux along the root was similar, showing a 10-fold greater efflux from the apical 0- to 5-mm region than from the 5- to 10-mm region. These results suggest that both Shanxi and Jiangxi possess an equal capacity for Al-dependent oxalic acid secretion. Another two potential Al resistance mechanisms, i.e. Al-induced alkalinization of rhizosphere pH and root inorganic phosphate release, were also not involved in their differential Al resistance. However, after longer treatments in Al (10 d), the concentrations of phosphorus and Al in the roots of the Al-resistant cultivar Jiangxi were significantly higher than those in Shanxi. Furthermore, more Al was localized in the cell walls of the resistant cultivar. All these results suggest that while Al-dependent oxalic acid secretion might contribute to the overall high resistance to Al stress of buckwheat, this response cannot explain the variation in tolerance between these two cultivars. We present evidence suggesting the greater Al resistance in buckwheat is further related to the immobilization and detoxification of Al by phosphorus in the root tissues.