[Show abstract][Hide abstract] ABSTRACT: High rates of phosphorus (P) are generally applied to vegetable crops, but this carries a risk of polluting the environment. There has been little research to define optimum soil P levels and strategies to reduce P requirements in the field. We hypothesized that high rates of P fertilization at the seedling stage followed by lower rates later could reduce total P fertilizer use in cucumber (Cucumis sativus L.). In this study, we explored the optimum P application via pot experiments in which three P levels at the seedling stage (0, 80, and 240 mg P kg−1 soil) were used in factorial combination with three P levels after transplanting (0, 80, and 160 mg P kg−1 soil). Results showed that P applied in the seedling stage was much more effective at maintaining optimal growth than in the field after transplanting. For example, 72 mg P pot−1 applied in the mode 240/0 (P application rates at the seedling vs transplant stages) produced a biomass dry weight (DW) of 17.7 g pot−1, whereas 360 mg P pot−1 applied in the mode 0/80 produced only 13.8 g pot−1. An ancillary study measured the depletion of P from solution by cucumber seedlings between 13 and 21 days after sowing. Over this period Vmax (the maximum uptake velocity) decreased from 1.18 to 0.50 nmol g−1 root dry weight s−1, while Km (the half-saturation constant where uptake is 50% of Vmax) increased from 5.60 to 8.14 μM. That indicates that since cucumber plants have a high capacity to absorb P as seedlings, it would be expected to reduce the P requirement in field soils. There are therefore efficiencies in applying higher P at the seedling stage and lower levels later.
Scientia Horticulturae 07/2015; 190. DOI:10.1016/j.scienta.2015.04.025 · 1.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Two Melaleuca species, M. cajuputi and M. bracteata, were compared to identify the factors determining their distinct aluminum (Al) resistance levels. The presence of Al in a liquid culture medium (maximum tested concentration, 2 mM) did not affect the growth of M. cajuputi, but severely inhibited the growth of M. bracteata. The Al content in the roots was 50% higher in Al-sensitive M. bracteata than in Al-resistant M. cajuputi. Al penetration and tissue damage were obvious in the roots of M. bracteata, but only mild in the roots of M. cajuputi. Relatively high levels of fumarate were released by the roots of M. cajuputi, but not by those of M. bracteata. Supplementation of Al-containing liquid media with fumarate resulted in a reduction of Al toxicity on M. bracteata. These results suggest that Al-resistant M. cajuputi releases fumarate from its roots, thereby detoxifying Al.
[Show abstract][Hide abstract] ABSTRACT: The phytotoxicity of aluminum (Al) ions can be alleviated by ammonium (NH4 (+) ) in rice and this effect has been attributed to the decreased Al accumulation in the roots. Here, the effects of different nitrogen forms on cell wall properties were compared in two rice cultivars differing in Al tolerance. An in vitro Al-binding assay revealed that neither NH4 (+) nor NO3 (-) altered the Al-binding capacity of cell walls, which were extracted from plants not previously exposed to N sources. However, cell walls extracted from NH4 (+) -supplied roots displayed lower Al-binding capacity than those from NO3 (-) -supplied roots when grown in non-buffered solutions. Fourier-transform infrared microspectroscopy analysis revealed that, compared with NO3 (-) -supplied roots, NH4 (+) -supplied roots possessed fewer Al-binding groups (-OH and COO-) and lower contents of pectin and hemicellulose. However, when grown in pH-buffered solutions, these differences in the cell wall properties were not observed. Further analysis showed that the Al-binding capacity and properties of cell walls were also altered by pHs alone. Taken together, our results indicate that the NH4 (+) -reduced Al accumulation was attributed to the altered cell wall properties triggered by pH decrease due to NH4 (+) uptake rather than direct competition for the cell wall binding sites between Al(3+) and NH4 (+) .
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[Show abstract][Hide abstract] ABSTRACT: Soil acidification is an increasing problem in agricultural production and ecological stability worldwide. An understanding of the mechanisms by which plants adapt to acidic soils would help address this problem. Poor plant growth in acidic soils results from a variety of factors, including proton toxicity; deficiencies in nitrogen, phosphorus, calcium, magnesium; and toxicities of various metals (aluminum (Al), manganese, iron). Aluminum toxicity is generally the primary limitation for plant growth in acidic soils. Although much research has focused on Al toxicity in recent decades, it is rarely the only limiting factor in acidic soils. The occurrence of Al toxicity depends on many other factors that coexist with Al in acidic soils. The interactions between Al and such factors are important determinants of Al toxicity to plants under field conditions. In this review, therefore, instead of focusing only on mechanisms of Al tolerance, we examine the effects of the interactions between Al and other limiting factors on plant adaptation to acidic soils. We summarize research on the interactions between Al and nitrogen, phosphorus, pH, and iron. Accordingly, three strategies are proposed to improve plant growth in acidic soils: a combined application of lime and nutrients, depending on the types of soils and plants; development of plant varieties tolerant to multiple stresses; and inoculation of plants with certain beneficial microbes. This review emphasizes the ability of plants to coadapt to multiple stresses in acidic soils.
[Show abstract][Hide abstract] ABSTRACT: The integrated effects of environmental factors on soil nitrification are largely unknown. Here, we performed a microcosm experiment to investigate the interactive effects of pH and NH4+ on nitrification activity in two acidic soils with different land use patterns (Anhui soil, a forest soil; Jiangxi soil, a brush land soil). Both soils were incubated under native pH and CaCO3-manipulated pH in the presence or absence of added ammonium for 60 days. The addition of CaCO3 alone did not change the nitrification activity of either soil. Ammonium addition stimulated nitrification in Anhui soil, but not in Jiangxi soil, and this stimulation was more pronounced with increased CaCO3. The ammonia monooxygenase (amoA) gene copy number of both ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) was much higher in Anhui soil than in Jiangxi soil. The amoA gene copy number of AOB in Anhui soil was more highly upregulated under CaCO3 + NH4+ than NH4+ during incubation. In Anhui soil, changes in the denaturing gradient gel electrophoresis (DGGE) fingerprint patterns of bacterial amoA genes were parallel to changes in the amoA gene copy number of AOB. In Jiangxi soil, DGGE could not be performed because the PCR for bacterial DGGE did not yield any products, while quantitative PCR revealed that the amoA gene copy number of AOB changed during incubation. These results suggest that AOB plays an important role in CaCO3-enhanced nitrification of Anhui soil with ammonium addition. The low nitrification rates of Jiangxi soil regardless of CaCO3 with or without NH4+ supply may be ascribed to the lower activity of both AOB and AOA, especially AOA.
[Show abstract][Hide abstract] ABSTRACT: Rhodotorula taiwanensis RS1 is a high-aluminum (Al)-tolerant yeast that can survive in Al concentrations up to 200 mM. The mechanisms for the high Al tolerance of R. taiwanensis RS1 are not well understood. To investigate the molecular mechanisms underlying Al tolerance and toxicity in R. taiwanensis RS1, Al toxicity-induced changes in the total soluble protein profile were analyzed using two-dimensional gel electrophoresis (2-DE) coupled with mass spectrometry. A total of 33 differentially expressed proteins responding to Al stress were identified from approximately 850 reproducibly detected proteins. Among them, the abundance of 29 proteins decreased and 4 increased. In the presence of 100 mM Al, the abundance of proteins involved in DNA transcription, protein translation, DNA defense, Golgi functions and glucose metabolism was decreased. By contrast, Al treatment led to increased abundance of malate dehydrogenase, which correlated with increased malate dehydrogenase activity and the accumulation of intracellular citrate, suggesting that Al-induced intracellular citrate could play an important role in detoxification of Al in R. taiwanensis RS1.
[Show abstract][Hide abstract] ABSTRACT: Objective:
To test the hypothesis that chronic infusion of angiotensin-(1-7) [Ang-(1-7)] may dose-dependently inhibit atherosclerotic lesion formation by targeting vascular smooth muscle cells and a large dose of Ang-(1-7) may stabilize mature plaque by targeting macrophages.
Approach and results:
In vivo, the effects of Ang-(1-7) on atherogenesis and plaque stability were observed in ApoE(-/-) mice fed a high-fat diet and chronic angiotensin II infusion. In vitro, the effects of Ang-(1-7) on vascular smooth muscle cells' proliferation and migration, and macrophage inflammatory cytokines were examined. Ang-(1-7) dose-dependently attenuated early atherosclerotic lesions and inhibited vascular smooth muscle cells' proliferation and migration via suppressing extracellular regulated protein kinase/P38 mitogen-activated protein kinase and janus kinase/signal transducers and activators of transcription activities and enhancing smooth muscle 22α and angiotensin II type 2 receptor expression. Ang-(1-7) treatment resulted in high contents of collagen and vascular smooth muscle cells, and low contents of macrophages and lipids in carotid mature plaques. Ang-(1-7) lowered the expression levels of proinflammatory cytokines and activities of matrix metalloproteinases in mature plaques.
Ang-(1-7) treatment inhibits early atherosclerotic lesions and increases plaque stability in ApoE(-/-) mice, thus providing a novel and promising approach to the treatment of atherosclerosis.
[Show abstract][Hide abstract] ABSTRACT: The complete mitochondrial genome of Rhodotorula taiwanensis RS1, an aluminum-tolerant Basidiomycota fungus, was determined and compared with the known mitochondrial genomes of 12 Basidiomycota species. The mitochondrial genome of R. taiwanensis RS1 is a circular DNA molecule of 40,392 bp and encodes the typical 15 mitochondrial proteins, 23 tRNAs, and small and large rRNAs as well as 10 intronic open reading frames. These genes are apparently transcribed in two directions and do not show syntenies in gene order with other investigated Basidiomycota species. The average G+C content (41%) of the mitochondrial genome of R. taiwanensis RS1 is the highest among the Basidiomycota species. Two introns were detected in the sequence of the atp9 gene of R. taiwanensis RS1, but not in that of other Basidiomycota species. Rhodotorula taiwanensis is the first species of the genus Rhodotorula whose full mitochondrial genome has been sequenced; and the data presented here supply valuable information for understanding the evolution of fungal mitochondrial genomes and researching the mechanism of aluminum tolerance in microorganisms.
[Show abstract][Hide abstract] ABSTRACT: Despite many studies on the high aluminum (Al) tolerance of rice (Oryza sativa), its exact mechanisms remain largely unknown. It is also unclear why Al improves growth of some plants. Our research on interactions between nitrogen (N) and Al may help to understand these phenomena. Previously, we found that ammonium-supplemented rice was more Al tolerant than nitrate-supplemented rice. Furthermore, Al-tolerant rice varieties preferred ammonium, while Al-sensitive ones preferred nitrate; in fact, Al tolerance was significantly correlated with the ammonium/nitrate preference among rice varieties. Al even enhanced growth of ammonium-supplemented rice, while it inhibited growth of nitrate-supplemented rice. Based on our own and other reports on N-Al interactions, we propose that intermediate products of N metabolism may play a role in rice Al tolerance. Al-enhanced ammonium utilization may explain why Al promotes growth of some plants, since Al often coexists with higher levels of ammonium than nitrate in acid soils.
[Show abstract][Hide abstract] ABSTRACT: Aluminum (Al) accumulation and long-distance transport in oil tea (Camellia oleifera Abel.), known to be an Al accumulator, was investigated. The average Al concentration in the embryo of oil tea seeds was 389 mg Al kg(-1) dry weight, which was higher than seeds of other Al accumulators. By partially suppressing leaf transpiration in the field, Al accumulation in leaves was depressed, which clarified the importance of xylem transport to Al accumulation in leaves. However, the effects of xylem transport alone could not sufficiently explain the high Al accumulation in the seasons when the leaf transpiration is weak, which hints the necessity of phloem transport working. Aluminum content in phloem exudates of barks provides another evidence of phloem transport. Images from scanning electron microscopy and energy-dispersive analysis also showed that Al was present in the phloem of oil tea petioles. Aluminum in oil tea could also be redistributed: higher concentrations of Al were found in leaves when Al was supplied to a different leaf of the same plant. In addition, Al was present in newly emerging roots of oil tea seedlings in which all original roots were excised prior to treatment, and a positive correlation existed between Al content in the newly formed roots and that in the leaves. The results using the empty seed coat technique showed that Al unloading via the phloem occurred during seed development. In conclusion, the results demonstrated that Al could be redistributed between leaves, from seeds to leaves, leaves to roots and leaves to seeds, which indicates that Al can be transported via the phloem in oil tea.
Tree Physiology 11/2012; 33(1). DOI:10.1093/treephys/tps117 · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The occurrence and distribution of heavy metals (including copper (Cu), lead (Pb), zinc (Zn), cadmium (Cd), chromium (Cr), cobalt (Co), nickel (Ni) and manganese (Mn)) in paddy soils from the Daye mining area were investigated by atomic absorption spectrophotometry (AAS) using the flame and graphite furnace method. The pollution of all metals investigated was found in paddy soil samples from the Daye mining area. Additionally, Cu, Pb, Zn and Cd concentrations at the sampling sites near the quarries and mines located in the central and eastern part of Daye were higher than those at the other sampling sites. Hierarchical cluster analysis and principal component analysis (PCA) of the heavy metal concentrations showed that the mine might be an important contributor to heavy metals contamination. PCA analysis extracted two factors that explained 67% of the total variables. The source of Zn, Cd, Cu and Pb would be primarily the deposition of aerosol particles emitted by metal smelting, manufacturing and traffic, acid mine drainage and metal mine waste rock and long-term stockpiling of tailings. Ni and Cr were controlled by parent material in the soils. Evaluation of heavy metals contamination of paddy soils indicated that the Cd contamination was the most widespread, followed Cu, Ni, Zn and Pb.
[Show abstract][Hide abstract] ABSTRACT: Background and AimsAcidic soils are dominated chemically by more ammonium and more available, so more potentially toxic, aluminium compared with neutral to calcareous soils, which are characterized by more nitrate and less available, so less toxic, aluminium. However, it is not known whether aluminium tolerance and nitrogen source preference are linked in plants.Methods
This question was investigated by comparing the responses of 30 rice (Oryza sativa) varieties (15 subsp. japonica cultivars and 15 subsp. indica cultivars) to aluminium, various ammonium/nitrate ratios and their combinations under acidic solution conditions.Key Results indicarice plants were generally found to be aluminium-sensitive and nitrate-preferring, while japonica cultivars were aluminium-tolerant and relatively ammonium-preferring. Aluminium tolerance of different rice varieties was significantly negatively correlated with their nitrate preference. Furthermore, aluminium enhanced ammonium-fed rice growth but inhibited nitrate-fed rice growth.Conclusions
The results suggest that aluminium tolerance in rice is antagonistic with nitrate preference and synergistic with ammonium preference under acidic solution conditions. A schematic diagram summarizing the interactions of aluminium and nitrogen in soil-plant ecosystems is presented and provides a new basis for the integrated management of acidic soils.
Annals of Botany 10/2012; 111(1). DOI:10.1093/aob/mcs234 · 3.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aims
Aluminum-tolerant wheat plants often produce more root exudates such as malate and phosphate than aluminum-sensitive ones under aluminum (Al) stress, which provides environmental differences for microorganism growth in their rhizosphere soils. This study investigated whether soil bacterial community composition and abundance can be affected by wheat plants with different Al tolerance.
Two wheat varieties, Atlas 66 (Al-tolerant) and Scout 66 (Al-sensitive), were grown for 60 days in acidic soils amended with or without CaCO3. Plant growth, soil pH, exchangeable Al content, bacterial community composition and abundance were investigated.
Atlas 66 showed better growth and lower rhizosphere soil pH than Scout 66 irrespective of CaCO3 amendment or not, while there was no significant difference in the exchangeable Al content of rhizosphere soil between the two wheat lines. The dominant bacterial community composition and abundance in rhizosphere soils did not differ between Atlas 66 and Scout 66, although the bacterial abundance in rhizosphere soil of both wheat lines was significantly higher than that in bulk soil. Sphingobacteriales, Clostridiales, Burkholderiales and Acidobacteriales were the dominant bacteria phylotypes.
The difference in wheat Al tolerance does not induce the changes in the dominant bacterial community composition or abundance in the rhizosphere soils.
Plant and Soil 06/2012; 367(1-2). DOI:10.1007/s11104-012-1473-3 · 2.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To explore a direct and causal relationship between vascular hepcidin and atherosclerotic plaque stability.
Accelerated atherosclerotic lesions were established by perivascular collar placement in apolipoprotein E-deficient (ApoE(-/-)) mice. Adenoviral overexpression of hepcidin in the carotid artery during plaque formation enhanced intraplaque macrophage infiltration and suppressed the contents of collagen and vascular smooth muscle cells, whereas hepcidin shRNA treatment exerts opposite effects. The overexpression or knockdown of hepcidin did not affect plaque lipid deposition but increased or decreased oxidized low-density lipoprotein (ox-LDL) levels within intraplaque macrophages. In cultured macrophages, ox-LDL not only increased reactive oxygen species formation, inflammatory cytokine production, and apoptosis but also upregulated hepcidin expression. However, hepcidin did not exaggerate the ox-LDL-induced activation of macrophages until an onset of erythrophagocytosis. Whereas hepcidin was critical for the upregulation of L-ferritin and H-ferritin in both ox-LDL-treated erythrophagocytosed macrophages and atherosclerotic plaques, the adding of iron chelators suppressed the intracellular lipid accumulation, reactive oxygen species formation, inflammatory cytokine expression, and apoptosis in erythrophagocytosed macrophages.
Hepcidin promotes plaque destabilization partly by exaggerating inflammatory cytokine release, intracellular lipid accumulation, oxidative stress, and apoptosis in the macrophages with iron retention.
[Show abstract][Hide abstract] ABSTRACT: Circulating levels of soluble lectin-like oxidized low-density lipoprotein receptor-1 (sLOX-1) play an important role in the development and progression of atherosclerosis. We hypothesized that the inflammatory marker C-reactive protein (CRP) might stimulate sLOX-1 release by activating tumor necrosis factor-α converting enzyme (TACE). Macrophages differentiated from THP-1 cells were stimulated with TNF-α and further treated with CRP in the absence or presence of specific inhibitors or small interfering RNA (siRNA). Our results showed that CRP increased sLOX-1 release from activated macrophages in a dose-dependent manner and that these effects were regulated by Fc γ receptor II (FcγRII)-mediated p47(phox) phosphorylation, reactive oxygen species (ROS) production, and TACE activation. CRP also enhanced sLOX-1 release from macrophages derived from peripheral blood mononuclear cells (PBMC) of patients with acute coronary syndrome (ACS). Pretreatment with antibody against FcγRII or with CD32 siRNA, p47(phox) siRNA, apocynin, N-acetylcysteine, tumor necrosis factor-α protease inhibitor 1 (TAPI-1) or TACE siRNA attenuated sLOX-1 release induced by CRP. CRP also elevated serum sLOX-1 levels in a rabbit model of atherosclerosis. Thus, CRP might stimulate sLOX-1 release, and the underlying mechanisms possibly involved FcγRII-mediated p47(phox) phosphorylation, ROS production, and TACE activation.
The Journal of Lipid Research 03/2011; 52(5):923-33. DOI:10.1194/jlr.M015156 · 4.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: NH4+ and NO3− supply often affect aluminum (Al) toxicity in plants growing in acidic soils. Lespedeza bicolor is a leguminous shrub well adapted to acid infertile soils. Secretion of organic acid anions has been demonstrated to be
the main mechanism responsible for its Al resistance. The objective of this study was to investigate how NH4+ and NO3− supply affect Al toxicity in L. bicolor and whether Al-induced organic acid anion secretion is involved in this effect. Long-term (36d) Al treatment increased L. bicolor root and shoot growth in a NH4+ medium. NH4+ treatment also decreased Al, Ca, Mg, Fe, and Mn contents in the roots of L. bicolor compared with NO3− treatment. After short-term (24h) Al treatment, L. bicolor seedlings had higher absolute root elongation and relative root elongation, and lower Al contents in root tips with NH4+ treatment than with NO3− treatment. In vitro Al adsorption kinetics experiment with isolated root cell wall showed that the accumulative amount of
Al adsorbed in root cell walls was lower with NH4+ treatment than with NO3− treatment. The roots of L. bicolor seedlings subjected to Al stress secreted less malate with NH4+ treatment than with NO3− treatment, whereas there was no significant difference in the malate content of L. bicolor roots between the treatments after exposure to Al. Taken together, these results show that NH4+ alleviated the toxicity of Al in L. bicolor in solution culture compared with NO3−, and this alleviating effect further resulted in decreased Al-induced malate secretion from L. bicolor roots.
KeywordsNitrogen form-Al toxicity-Malate-Alleviation-Lespedeza bicolor
Plant and Soil 12/2010; 337(1):389-398. DOI:10.1007/s11104-010-0535-7 · 2.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rice (Oryza sativa) as a staple food, provides a major source of dietary selenium (Se) for humans, which essentially requires Se, however, the molecular mechanism for Se uptake is still poorly understood. Herein, we show evidence that the uptake of selenite, a main bioavailable form of Se in paddy soils, is mediated by a silicon (Si) influx transporter Lsi1 (OsNIP2;1) in rice. Defect of OsNIP2;1 resulted in a significant decrease in the Se concentration of the shoots and xylem sap when selenite was given. However, there was no difference in the Se concentration between the wild-type rice and mutant of OsNIP2;1 when selenate was supplied. A short-term uptake experiment showed that selenite uptake greatly increased with decreasing pH in the external solution. Si as silicic acid did not inhibit the Se uptake from selenite in both rice and yeast (Saccharomyces cerevisiae) at low pHs. Expression of OsNIP2;1 in yeast enhanced the selenite uptake at pH 3.5 and 5.5 but not at pH 7.5. On the other hand, defect of Si efflux transporter Lsi2 did not affect the uptake of Se either from selenite or selenate. Taken together, our results indicate that Si influx transporter OsNIP2;1 is permeable to selenite.
[Show abstract][Hide abstract] ABSTRACT: Demand for low-input nitrogen sustainable rice is increasing to meet the need for environmentally friendly agriculture and
thus development of rice with high nitrogen use efficiency (NUE) is a major objective. Hence, understanding how rice responds
to growth under low-nitrogen conditions is essential to devise new ways of manipulating genes to improve rice NUE. In this
study, using two rice varieties with different seedling-stage NUE obtained from previous field experiments, we investigated
the physiological and molecular responses of young rice to low-nitrogen conditions. Our results suggest that glutamine synthetase
(GS) and NADH-dependent glutamate synthase (NADH-GOGAT) play important roles in N assimilation of seedling rice roots under
low-nitrogen conditions; the regulatory mechanisms of GS and NADH-GOGAT in seedling rice roots do not occur at the transcription
level, and may be posttranscriptional; OsAMT1;1 play important roles in rice N acquisition by partially regulating N uptake under low-nitrogen conditions; and OsAMT1;1 and OsNRT2;1 also play important roles in rice N acquisition by partially regulating root growth and development under low-nitrogen conditions.
The challenge for future studies is to characterize the functional roles of GS, NADH-GOGAT, OsAMT1;1, and OsNRT2;1 in young rice NUE using RNAi and mutant techniques.
Plant and Soil 01/2009; 326(1):291-302. DOI:10.1007/s11104-009-0007-0 · 2.95 Impact Factor