[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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Plant Cell and Environment 12/2014; · 5.91 Impact Factor
[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.
Biochimica et Biophysica Acta 07/2013; · 4.66 Impact Factor
[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: 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: 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.
[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.
[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: 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 01/2010; 337(1):389-398. · 3.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aluminium (Al) toxicity and phosphorus (P) deficiency often co-exist in acidic soils and limit crop production worldwide. Lespedeza bicolor is a leguminous forage species that grows very well in infertile, acidic soils. The objective of this study was to investigate the effects of Al and P interactions on growth of Lespedeza and the distributions of Al and P in two different Al-resistant species, and to explore whether P can ameliorate the toxic effect of Al in the two species.
Two species, Lespedeza bicolor and L. cuneata, were grown for 30 d with alternate Al and P treatments in a hydroponics system. Harvested roots were examined using a root-system scanner, and the contents of Al, P and other nutrient elements in the plants were determined using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Haematoxylin staining was used to observe the distribution of Al in the roots of seedlings. After pre-culture with or without P application, organic acids in the exudates of roots exposed to Al were held in an anion-exchange resin, eluted with 2 m HCl and then analysed using high-performance liquid chromatography (HPLC).
Lespedeza bicolor exhibited a stronger Al resistance than did L. cuneata; Al exclusion mechanisms may mainly be responsible for resistance. P application alleviated the toxic effect of Al on root growth in L. bicolor, while no obvious effects were observed in L. cuneata. Much less Al was accumulated in roots of L. bicolor than in L. cuneata after P application, and the P contents in both roots and shoots increased much more for L. bicolor than for L. cuneata. Lespedeza bicolor showed a higher P/Al ratio in roots and shoots than did L. cuneata. P application decreased the Al accumulation in root tips of L. bicolor but not in L. cuneata. The amount of Al-induced organic acid (citrate and malate) exudation from roots pre-cultured with P was much less than from roots without P application; no malate and citrate exudation was detected in L. cuneata.
P enhanced Al resistance in the Al-resistant L. bicolor species but not in the Al-sensitive L. cuneata under relatively high Al stress, although P in L. cuneata might also possess an alleviative potential. Enhancement of Al resistance by P in the resistant species might be associated with its more efficient P accumulation and translocation to shoots and greater Al exclusion from root tips after P application, but not with an increased exudation of organic acids from roots.
Annals of Botany 09/2008; 102(5):795-804. · 3.45 Impact Factor
[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 326(1):291-302. · 3.24 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.
[Show abstract][Hide abstract] ABSTRACT: Al stress and ammonium–nitrogen nutrition often coexist in acidic soils due to their low pH and weak nitrification ability.
Rice is the most Al-resistant species among small grain cereal crops and prefers NH4
+ as its major inorganic nitrogen source. This study investigates the effects of NH4
+ and NO3
− on Al toxicity and Al accumulation in rice, and thereby associates rice Al resistance with its NH4
+ preference. Two rice subspecies, indica cv. Yangdao6 and japonica cv. Wuyunjing7, were used in this study. After treatment with or without Al under conditions of varying NH4
+ and NO3
− supply, rice seedlings were harvested for the determination of root elongation, callose content, biomass, Al concentration
and medium pH. The results indicated that Wuyunjing7 was more Al-resistant and NH4
+-preferring than Yangdao6. NH4
+ alleviated Al toxicity in two cultivars compared with NO3
−. Both NH4
+-Al supply and pretreatment with NH4
+ reduced Al accumulation in roots and root tips compared with NO3
+ decreased but NO3
− increased the medium pH, and root tips accumulated more Al with a pH increase from 3.5 to 5.5. Increasing the NO3
− concentration enhanced Al accumulation in root tips but increasing the NH4
+ concentration had the opposite effect. These results show NH4
+ alleviates Al toxicity for rice and reduces Al accumulation in roots compared with NO3
−, possibly through medium pH changes and ionic competitive effects. Making use of the protective effect of NH4
+, in which the Al resistance increases, is advised for acidic soils, and the hypothesis that rice Al resistance is associated
with the preferred utilization of NH4
+ is suggested.
Plant and Soil 315(1):107-121. · 3.24 Impact Factor