Effects of UV-B radiation on the survival, egg hatchability and transcript expression of antioxidant enzymes in a high-temperature adapted strain of Neoseiulus barkeri.

Biological control of spider mites in hot and dry weather is a serious technical issue. A high-temperature adapted strain (HTAS) of the predatory mite Neoseiulus barkeri Hughes was selected from its conventional strain (CS), via long-term heat acclimation and frequent heat hardenings in our previous studies. However, the environment of high temperature is usually associated with enhanced ultraviolet (UV) radiation. In the present study, the physiological effects of UV-B radiation on survival rate and egg damage of N. barkeri were investigated, as well as the activities and expression profiles of antioxidant enzymes to UV-B radiation stress. UV-B radiation had deleterious effects on egg hatchability and survival of N. barkeri. Adults of the HTAS strain were less UV-B resistant than those of the CS strain; they also had lower levels of enzymatic activity of superoxide dismutase (SOD) and catalase against oxidative damage and weaker upregulation of SOD genes. The mRNA expression of three SOD genes of CS adult females immediately increased whereas that of HTAS showed almost no difference under UV-B stress for 1 h. The results showed the HTAS of N. barkeri had lower fitness under UV-B stress compared with the CS of N. barkeri. These results suggested that long-term heat acclimation may exert a profound impact on the developmental physiology of N. barkeri.

Short-term efficacy and influencing factors of conventional chemotherapy combined with irinotecan in patients with advanced gastric cancer.

BACKGROUND: Gastric cancer is one of the most common cancers worldwide, with a 5-year survival rate of only 20%. The age of onset of gastric cancer is in line with the general rule of cancer. Most of them occur after middle age, mostly between 40 and 60 years old, with an average age of about 50 years old, and only 5% of patients are under 30 years old. The incidence of male is higher than that of female. AIM: To investigate the short-term efficacy and influencing factors of chemotherapy combined with irinotecan in patients with advanced gastric cancer. METHODS: Eighty patients with advanced gastric cancer who were treated in our hospital from January 2019 to January 2022 were selected. The patients were divided into an observation group (n = 40) and control group (n = 40) by the envelope method. The control group was given preoperative routine chemotherapy. The observation group was treated with irinotecan in addition to the chemotherapy given to the control group. The short-term efficacy of treatment in the two groups, as well as tumor marker levels and quality of life before and after treatment were evaluated. RESULTS: The short-term treatment effect in the observation group was better than that in the control group (P < 0.05), and the total effective rate was 57.50%. The age and proportion of tumor node metastasis (TNM) stage IV patients with ineffective chemotherapy in the observation group were (65.12 ± 5.71) years and 52.94%, respectively, which were notably higher than those of patients with effective chemotherapy (P < 0.05), while the Karnofsky Performance Scale score was (67.70 ± 3.83) points, which was apparently lower than that of patients with effective chemotherapy (P < 0.05). After 3 mo of treatment, the SF-36 scale scores of physiological function, energy, emotional function, and mental health in the observation group were 65.12 ± 8.14, 54.76 ± 6.70, 47.58 ± 7.22, and 66.16 ± 8.11 points, respectively, which were considerably higher than those in the control group (P < 0.05). The incidence rates of grade III-IV diarrhea and grade III-IV thrombocytopenia in the observation group were 32.50% and 25.00%, respectively, which were markedly higher than those in the control group (P < 0.05). CONCLUSION: Chemotherapy combined with irinotecan in patients with advanced gastric cancer has a good short-term efficacy and can significantly reduce serum tumor markers and improve the quality of life of patients. The efficacy may be affected by the age and TNM stage of the patients, and its long-term efficacy needs further study.

Research progress in biological control of tomato bacterial wilt.

Bacterial wilt caused by the infection of Ralstonia solanacearum, is one of the most harmful diseases to tomatoes, one of the most important greenhouse vegetables in China. R. solanacearum can survive and remain active in the deep soil for a long time, and the chemical control of tomato bacterial wilt is consequently limited. In this study, we introduced the characteristics of tomato bacterial wilt disease and the types of R. solanacearum, and systematically reviewed the research progresses of biological control methods from the aspects of botanical insecticides, agricultural antibiotics, biocontrol bacteria. We emphatically introduced the principle and current status of these methods, discussed the limitations and the improvement strategies, and prospected a new environmental protection and efficient biological control system based on micro-ecological regulation would be the development direction of biological control of tomato bacterial wilt.

Mechanism of polycyclic aromatic hydrocarbons degradation in the rhizosphere of Phragmites australis: Organic acid co-metabolism, iron-driven, and microbial response.

Microbial co-metabolism is crucial for the efficient biodegradation of polycyclic aromatic hydrocarbons (PAHs); however, their intrinsic mechanisms remain unclear. To explore the co-metabolic degradation of PAHs, root organic acids (ROAs) (phenolic ROAs: caffeic acid [CA] and ferulic acid [FA]; non-phenolic ROAs: oxalic acid [OA]) were exogenously added as co-metabolic substrates under high (HFe) and low (LFe) iron levels in this study. The results demonstrated that more than 90% of PAHs were eliminated from the rhizosphere of Phragmites australis. OA can promote the enrichment of unrelated degrading bacteria and non-specific dioxygenases. FA with a monohydroxy structure can activate hydroxylase; however, it relies on phytosiderophores released by plants (such as OA) to adapt to stress. Therefore, non-specific co-metabolism occurred in these units. The best performance for PAH removal was observed in the HFe-CA unit because: (a) HFe concentrations enriched the Fe-reducing and denitrifying bacteria and promoted the rate-limiting degradation for PAHs as the enzyme cofactor; (b) CA with a dihydroxyl structure enriched the related degrading bacteria, stimulated specific dioxygenase, and activated Fe to concentrate around the rhizosphere simultaneously to perform the specific co-metabolism. Understanding the co-metabolic degradation of PAHs will help improve the efficacy of rhizosphere-mediated remediation.

Innate Root Exudates Contributed to Contrasting Coping Strategies in Response to Ralstonia solanacearum in Resistant and Susceptible Tomato Cultivars.

Tomato cultivars with contrasting resistance to pathogens regulate root exudates differentially in response to Ralstonia solanacearum attacks. However, strategies using innate root exudates against infection remain unknown. This study analyzed the innate root exudates of two tomato cultivars and their functions in regulating R. solanacearum infection. The innate root exudates differed between the two cultivars. Astaxanthin released from resistant plants inhibited colonization by R. solanacearum but promoted motility, while neferine released from susceptible plants suppressed motility and colonization. The secretion of astaxanthin in resistant tomatoes promoted the growth of biocontrol fungi in soil and reduced the abundance of pathogenic fungi. Neferine secreted by the susceptible cultivar inhibited the relative abundance of the bacterial-biocontrol-related Bacillus genus, indirectly reducing the soil's immune capacity. This study revealed contrasting strategies using root exudates in resistant and susceptible tomato cultivars to cope with R. solanacearum infection, providing a basis for breeding disease-resistant cultivars.

[Research progress on primers and molecular ecology of comammox Nitrospira]. / å®Œå ¨æ°¨æ°§åŒ–èŒçš„åˆ†å­ç”Ÿæ€å­¦ç ”ç©¶è¿›å±•.

Nitrification is a key process in nitrogen cycling, which has received considerable attention in the research field of soil biochemistry. In 2015, the discovery of complete ammonia oxidizers (Comammox) challenged conventional two-step nitrification perspective, which represented a paradigm shift in the understanding of soil nitrogen cycling. Comammox are a group of microorganisms capable of conducting both steps of nitrification. In this review, we summarized current understan-ding of the molecular ecology of comammox, including specific molecular biomarkers for comammox, phylogenetic and genomic surveys of comammox and particularly the distribution, diversity and ecological significance of comammox in soil. Further studies should focus on: 1) designing specific molecular biomarkers to examine the distribution and diversity of comammox; 2) optimizing cultivation techniques to isolate/enrich comammox cultures and expending our insights into physiological traits of comammox; 3) characterizing their distribution and in situ activities to elucidate the contribution of comammox processes to soil nitrification and their ecological features, which may assist in unco-vering the mechanisms of nitrogen cycling and promote the environmental protection of soil ecosystem.

Comparative Transcriptome and Proteome Analysis of Heat Acclimation in Predatory Mite Neoseiulus barkeri.

In our previous study, we reported a high temperature adapted strain (HTAS) of the predatory mite Neoseiulus barkeri was artificially selected via a long-term heat acclimation (35°C) and frequent heat hardenings. To understand the molecular basis of heat acclimation, 'omics' analyses were performed to compare the differences between HTAS female adults to conventional strain (CS) at transcriptional and translational levels. We obtained a total of 5,374 differentially expressed genes and 500 differentially expressed proteins. Among them, 119 transcripts had concurrent transcription and translation profiles. It's conserved that some processes, such as high expression of heat shock protein (HSP) genes, involved in heat tolerance of transcriptome analyses, while many protective enzymes including glutathione S-transferase, superoxide dismutase, peroxidase, and cytochrome P450 displayed down-regulated expression. KEGG analysis mapped 4,979 and 348 differentially expressed genes and proteins, to 299 and 253 pathways, respectively. The mitogen-activated protein kinases (MAPK) signaling pathway may provide new insights for the investigation of the molecular mechanisms of heat tolerance. Correlation enriched pathways indicated that there were four pathways associated with heat acclimation involving in energy metabolism and immunity. In addition, the expression patterns of ten randomly selected genes including HSP were consistent with the transcriptome results obtained through quantitative real-time PCR. Comparisons between transcriptome and proteome results indicated the upregulation of HSPs and genes participated in ATP production, immunity and energy metabolism process. A majority of antioxidant-related genes and detoxication-related genes were down-regulated suggesting a fitness cost of heat acclimation. Our results demonstrated that heat tolerance during a long-time acclimation of N. barkeri is a fairly complicated process of physiological regulations. These findings also contribute to a better understanding of the mechanisms of thermal responses of phytoseiid mites which could provide useful information for biological control through natural enemies.

Disorganized distribution of homogalacturonan epitopes in cell walls as one possible mechanism for aluminium-induced root growth inhibition in maize.

BACKGROUND AND AIMS: Aluminium (Al) toxicity is one of the most severe limitations to crop production in acid soils. Inhibition of root elongation is the primary symptom of Al toxicity. However, the underlying basis of the process is unclear. Considering the multiple physiological and biochemical functions of pectin in plants, possible involvement of homogalacturonan (HG), one of the pectic polysaccharide domains, was examined in connection with root growth inhibition induced by Al. METHODS: An immunolabelling technique with antibodies specific to HG epitopes (JIM5, unesterified residues flanked by methylesterifed residues; JIM7, methyl-esterified residues flanked by unesterified residues) was used to visualize the distribution of different types of HG in cell walls of root apices of two maize cultivars differing in Al resistance. KEY RESULTS: In the absence of Al, the JIM5 epitope was present around the cell wall with higher fluorescence intensity at cell corners lining the intercellular spaces, and the JIM7 epitope was present throughout the cell wall. However, treatment with 50 microm Al for 3 h produced 10 % root growth inhibition in both cultivars and caused the disappearance of fluorescence in the middle lamella of both epitopes. Prolonged Al treatment (24 h) with 50 % root growth inhibition in 'B73', an Al-sensitive cultivar, resulted in faint and irregular distribution of both epitopes. In 'Nongda3138', an Al-resistant cultivar, the distribution of HG epitopes was also restricted to the lining of intercellular spaces when a 50 % inhibition to root growth was induced by Al (100 microm Al, 9 h). Altered distribution of both epitopes was also observed when of roots were exposed to 50 microm LaCl(3) for 24 h, resulting in 40 % inhibition of root growth. CONCLUSIONS: Changes in HG distribution and root growth inhibition were highly correlated, indicating that Al-induced perturbed distribution of HG epitopes is possibly involved in Al-induced inhibition of root growth in maize.

Protecting cell walls from binding aluminum by organic acids contributes to aluminum resistance.

Aluminum-induced secretion of organic acids from the root apex has been demonstrated to be one major Al resistance mechanism in plants. However, whether the organic acid concentration is high enough to detoxify Al in the growth medium is frequently questioned. The genotypes of Al-resistant wheat, Cassia tora L. and buckwheat secrete malate, citrate and oxalate, respectively. In the present study we found that at a 35% inhibition of root elongation, the Al activities in the solution were 10, 20, and 50 muM with the corresponding malate, citrate, and oxalate exudation at the rates of 15, 20 and 21 nmol/cm(2) per 12 h, respectively, for the above three plant species. When exogenous organic acids were added to ameliorate Al toxicity, twofold and eightfold higher oxalate and malate concentrations were required to produce the equal effect by citrate. After the root apical cell walls were isolated and preincubated in 1 mM malate, oxalate or citrate solution overnight, the total amount of Al adsorbed to the cell walls all decreased significantly to a similar level, implying that these organic acids own an equal ability to protect the cell walls from binding Al. These findings suggest that protection of cell walls from binding Al by organic acids may contribute significantly to Al resistance.

Identification of Wolbachia-Responsive miRNAs in the Small Brown Planthopper, Laodelphax striatellus.

Laodelphax striatellus is naturally infected with the Wolbachia strain wStri, which induces strong cytoplasmic incompatibility of its host. MicroRNAs (miRNAs) are a class of endogenous non-coding small RNAs that play a critical role in the regulation of gene expression at post-transcriptional level in various biological processes. Despite various studies reporting that Wolbachia affects the miRNA expression of their hosts, the molecular mechanism underlying interactions between Wolbachia and their host miRNAs has not been well understood. In order to better understand the impact of Wolbachia infection on its host, we investigated the differentially expressed miRNAs between Wolbachia-infected and Wolbachia-uninfected strains of L. striatellus. Compared with uninfected strains, Wolbachia infection resulted in up-regulation of 18 miRNAs and down-regulation of 6 miRNAs in male, while 25 miRNAs were up-regulated and 15 miRNAs were down-regulated in female. The target genes of these differentially expressed miRNAs involved in immune response regulation, reproduction, redox homeostasis and ecdysteroidogenesis were also annotated in both sexes. We further verified the expression of several significantly differentially expressed miRNAs and their predicted target genes by qRT-PCR method. The results suggested that Wolbachia appears to reduce the expression of genes related to fertility in males and increase the expression of genes related to fecundity in females. At the same time, Wolbachia may enhance the expression of immune-related genes in both sexes. All of the results in this study may be helpful in further exploration of the molecular mechanisms by which Wolbachia affects on its hosts.

[Effects of changes in water status on soil microbes and their response mechanism: A review]. / æ°´åˆ†æ¡ä»¶å˜åŒ–å¯¹åœŸå£¤å¾®ç”Ÿç‰©çš„å½±å“åŠå ¶å“åº”æœºåˆ¶ç ”ç©¶è¿›å±•.

Soil microbes play essential roles in maintaining terrestrial ecosystem services. Soil moisture is a primary determinant of soil microbial activities and ecosystem functions, which may fluctuate dramatically with the altered precipitation patterns and extreme drought caused by the ongoing global climate change. Due to the distinct soil microbial tolerance and life-strategy approaches to drought stress and different water status, fluctuation of soil moisture has a direct impact on microbial activities and community structure, thereby profoundly affecting microbial-mediated processes and ecosystem functions. Thus, it is of great significance to understand the dynamics and mechanisms that underlie the microbial responses to soil water status. In this review, we summarized recent progress in the study of responses of soil microbial activities (e.g. soil respiration and enzyme activities) and community structure to soil water status. We summarized underlying microbial physiological and ecological mechanisms, particularly 1) the cellular physiological accommodation such as osmolyte accumulation, exopolysaccharide production and transition into dormant states, and 2) the ecological strategies such as stress-resistant gene transfer and functional redundancy. Therefore, this investigation on the underlying relationship between soil microbial assembly and ecosystem functions under different water status could further demonstrate the microbially-mediated soil biogeochemical processes and provide a theoretical basis for future research and modelling of terrestrial ecosystem responses to climate change.

Advanced primary amelanotic malignant melanoma of the esophagus: A case report.

BACKGROUND: Primary malignant melanoma of the esophagus accounts for 0.1%-0.2% of all esophageal malignancies, including melanotic and amelanotic melanomas. Primary amelanotic malignant melanoma of the esophagus is extremely rare, and only about 20 cases have been published in the literature to date. Most primary malignant melanomas of the esophagus are diagnosed following development of metastatic lesions and thus have a very poor prognosis. The median survival duration of patients with metastatic melanoma has been reported to be 6.2 mo. CASE SUMMARY: A 49-year-old woman was referred to our hospital with a diagnosis of esophageal cancer. Endoscopy, biopsy, imaging evaluation, and physical examination at our hospital indicated a diagnosis of advanced primary amelanotic malignant melanoma of the esophagus. Immunohistochemical staining confirmed melanoma. Nuclear medicine examination revealed a left iliac bone metastatic lesion. After discharge, the patient self-administered apatinib for 3 mo, followed by oral treatment with Chinese medicines (also self-administered) for 2 mo. No treatments had been taken since then. The patient has survived with no growth out to the most recent follow-up (24 mo post diagnosis), and she always presented with a positive attitude about her condition during this period. CONCLUSION: Survival following metastatic melanoma might be related to the pharmaceutical and Chinese medicine treatment and the patient's positive attitude.

Response to Multiple Stressors: Enhanced Tolerance of Neoseiulus barkeri Hughes (Acari: Phytoseiidae) to Heat and Desiccation Stress through Acclimation.

Organisms are always confronted with multiple stressors simultaneously. Combinations of stressors, rather than single stressor, may be more appropriate in evaluating the stress they experience. N. barkeri is one of predatory mite species that are commercialized for controlling spider mites. However, their biological control efficiency was often reduced because of high temperature and desiccation in summer. To understand how to improve the tolerance of N. barkeri to combined heat and desiccation stress, we pre-exposed the adult female of N. barkeri to high temperature, desiccation and high temperature × desiccation stress for acclimation. After proper recovery time, mites were subjected to high temperature × desiccation stress again to detect the acclimation effects. The results are as follows: (1) No decrease in mortality rate were observed under high temperature × desiccation stress after heat acclimation. Instead, it increased significantly with acclimation temperature and time. (2) Dehydration acclimation both at 25 °C and high temperatures reduced mortality rate under high temperature × desiccation stress. Mortality rate was only significantly correlated with the amount of water loss, but not with temperature or water loss rate in acclimation, suggesting the increased tolerance is related to dehydration stress rather than heat stress. Among all acclimations, chronic dehydration at 25 °C, 50% relative humidity were the most effective treatment. This study indicated dehydration acclimation is effective to enhance tolerance of N. barkeri to combined heat and desiccation stress, which can improve the efficiency of biological control under multiple stressors.

Effects of coumestrol on neonatal and adult mice osteoblasts activities.

Estrogen replacement therapy has been shown to reduce postmenopausal osteoporosis. In the present study, we examined the effects of the phytoestrogen coumestrol on neonatal and adult osteoblasts metabolism. Two different sources of osteoblast cells (neonatal mice calvaria and adult mice long bone) cultures were used in this study. The effects of coumestrol on the cellular activities were analyzed by the mitochondrial tetrazolium (MTT) assay, secretion of alkaline phosphatase (ALP), intracellular calcium content (Ca), and the gene expression of bone matrix protein, estrogen receptors (ER-alpha, ER-beta), and osteoprotegerin (OPG) and osteoprotegerin ligand (OPGL). The results showed that the proliferation of neonatal mice osteoblast cells was enhanced by treatment of coumestrol. In the presence of 10(-9)M coumestrol, the osteoblast proliferation attained 139.5% of the control and that the coumestrol can increase the intracellular calcium contents. Type I collagen gene expression was upregulated 167% at the 1st day's culture; ALP gene expression was upregulated 360% at the 7th day's culture; while the osteocalcin gene expression was upregulated 222% at the 14th day's culture. When adult mice osteoblasts were cultured in the presence of 10(-9)M coumestrol, the osteoblasts population increased significantly earlier and attained its maximal effect at the 21st day's culture with 207.4% of control group. The content of ER-beta and osteoprotegerin secretion by neonatal mice control cells gradually increased during osteoblasts differentiation, whereas the ER-alpha and OPGL content were decreased in this study. The cellular responses to the estradiol and counmestrol were quite different in the osteoblasts derived from different age.

Evaluation of Neoseiulus barkeri (Acari: Phytoseiidae) for Control of Eotetranychus kankitus (Acari: Tetranychidae).

Eotetranychus kankitus Ehara (Acari: Tetranychidae) is an important pest in Chinese citrus orchards. In the present study, we aimed to evaluate the potential of Neoseiulus barkeri (Hughes) (Acari: Phytoseiidae) for the biological control of E. kankitus. A two-sex life table of E. kankitus and N. barkeri was constructed to estimate development and fecundity. The functional response and stage-specific predation rate were analyzed to evaluate predation capacity. In addition, a timing model was used to project populations of E. kankitus with release of N. barkeri. Results showed that N. barkeri was able to develop and reproduce when fed on E. kankitus. The functional responses of N. barkeri on different stages of E. kankitus all fit the Holling II disc equation. When mixed stages of E. kankitus coexisted, N. barkeri mainly consumed larvae and nymphs. Based on the life tables and stage-specific predation rates, population projection revealed the stage structure and growth rate of N. barkeri on E. kankitus. Although E. kankitus had the higher growth rate, it was maintained at a low population level for several weeks after release of N. barkeri. The results highlighted the potential for utilizing N. barkeri as a biological control agent of E. kankitus.

Does Long-Term Feeding on Alternative Prey Affect the Biological Performance of Neoseiulus barkeri (Acari: Phytoseiidae) on the Target Spider Mites?

The predatory mite Neoseiulus barkeri (Hughes) is a good biological control agent for many small sucking pests. We aimed to determine whether rearing long term on alternative prey versus target prey species affected the performance of N. barkeri. Therefore, we investigated the prey preference, life tables, and population parameters of N. barkeri between alternative prey Tyrophagus putrescentiae (Schrank) and three species of spider mites, Tetranychus urticae Koch, Panonychus citri (McGregor), and Eotetranychus kankitus Ehara. We found that N. barkeri preferred the tetranychid mites to the alternative prey. Between the tetranychid mites, the predator consumed more P. citri and E. kankitus than T. urticae. When reared on T. urticae, the total developmental time and longevity of N. barkeri were the longest, whereas the intrinsic rate of increase was the lowest, indicating that the biotic fitness of predatory mite preyed on target of T. urticae was higher than on alternative prey of T. putrescentiae. However, total developmental time, longevity, and fecundity did not differ between N. barkeri reared on T. putrescentiae and P. citri, although these parameters were higher than those for mites reared on E. kankitus, indicating that the predatory mite reared on T. putrescentiae may not be affected to control P. citri, and that coexistence of P. citri and E. kankitus may enhance the control efficiency of N. barkeri. Altogether, our results demonstrated that long-term feeding on the alternative prey T. putrescentiae did not affect the performance of the predatory mite N. barkeri on various target spider mites.

Cell wall polysaccharides are specifically involved in the exclusion of aluminum from the rice root apex.

Rice (Oryza sativa) is the most aluminum (Al)-resistant crop species among the small-grain cereals, but the mechanisms responsible for this trait are still unclear. Using two rice cultivars differing in Al resistance, rice sp. japonica 'Nipponbare' (an Al-resistant cultivar) and rice sp. indica 'Zhefu802' (an Al-sensitive cultivar), it was found that Al content in the root apex (0-10 mm) was significantly lower in Al-resistant 'Nipponbare' than in sensitive 'Zhefu802', with more of the Al localized to cell walls in 'Zhefu802', indicating that an Al exclusion mechanism is operating in 'Nipponbare'. However, neither organic acid efflux nor changes in rhizosphere pH appear to be responsible for the Al exclusion. Interestingly, cell wall polysaccharides (pectin, hemicellulose 1, and hemicellulose 2) in the root apex were found to be significantly higher in 'Zhefu802' than in 'Nipponbare' in the absence of Al, and Al exposure increased root apex hemicellulose content more significantly in 'Zhefu802'. Root tip cell wall pectin methylesterase (PME) activity was constitutively higher in 'Zhefu802' than in 'Nipponbare', although Al treatment resulted in increased PME activity in both cultivars. Immunolocalization of pectins showed a higher proportion of demethylated pectins in 'Zhefu802', indicating a higher proportion of free pectic acid residues in the cell walls of 'Zhefu802' root tips. Al adsorption and desorption kinetics of root tip cell walls also indicated that more Al was adsorbed and bound Al was retained more tightly in 'Zhefu802', which was consistent with Al content, PME activity, and pectin demethylesterification results. These responses were specific to Al compared with other metals (CdCl(2), LaCl(3), and CuCl(2)), and the ability of the cell wall to adsorb these metals was also not related to levels of cell wall pectins. All of these results suggest that cell wall polysaccharides may play an important role in excluding Al specifically from the rice root apex.

Magnesium enhances aluminum-induced citrate secretion in rice bean roots (Vigna umbellata) by restoring plasma membrane H+-ATPase activity.

We demonstrated that magnesium (Mg) can alleviate aluminum (Al) toxicity in rice bean [Vigna umbellata (Thunb.) Ohwi & Ohashi] more effectively than is expected from a non-specific cation response. Micromolar concentrations of Mg alleviated the inhibition of root growth by Al but not by lanthanum, and neither strontium nor barium at the micromolar level alleviates Al toxicity. Aluminum also induced citrate efflux from rice bean roots, and this response was stimulated by inclusion of 10 microM Mg in the treatment solution. The increase in the Al-induced citrate efflux by Mg paralleled the improvement in root growth, suggesting that the ameliorative effect of Mg might be related to greater citrate efflux. Vanadate (an effective H+-ATPase inhibitor) decreased the Al-induced citrate efflux, while addition of Mg partly restored the efflux. Mg addition also increased the activity of Al-reduced plasma membrane H+-ATPase, as well as helping to maintain the Mg and calcium contents in root apices. We propose that the addition of Mg to the toxic Al treatment helps maintain the tissue Mg content and the activity of the plasma membrane H+-ATPase. These changes enhanced the Al-dependent efflux of citrate which provided extra protection from Al stress.

Citrate transporters play a critical role in aluminium-stimulated citrate efflux in rice bean (Vigna umbellata) roots.

BACKGROUND AND AIMS: Aluminium (Al) stimulates the efflux of citrate from apices of rice bean (Vigna umbellata) roots. This response is delayed at least 3 h when roots are exposed to 50 microm Al, indicating that some inducible processes leading to citrate efflux are involved. The physiological bases responsible for the delayed response were examined here. METHODS: The effects of several antagonists of anion channels and citrate carriers, and of the protein synthesis inhibitor, cycloheximide (CHM) on Al-stimulated citrate efflux and/or citrate content were examined by high-pressure liquid chromatography (HPLC) or an enzymatic method. KEY RESULTS: Both anion channel inhibitors and citrate carrier inhibitors can inhibit Al-stimulated citrate efflux, with anthracene-9-carboxylic acid (A-9-C, an anion channel inhibitor) and phenylisothiocyanate (PI, a citrate carrier inhibitor) the most effective inhibitors. A 6 h pulse of 50 microm Al induced a significant increase of citrate content in root apices and release of citrate. However, the increase in citrate content preceded the efflux. Furthermore, the release of citrate stimulated by the pulse treatment was inhibited by both A-9-C and PI, indicating the importance of the citrate carrier on the mitochondrial membrane and the anion channel on the plasma membrane for the Al-stimulated citrate efflux. CHM (20 microm) also significantly inhibited Al-stimulated citrate efflux, confirming that de novo protein synthesis is required for Al-stimulated citrate efflux. CONCLUSIONS: These results indicate that the activation of genes possibly encoding citrate transporters plays a critical role in Al-stimulated citrate efflux.