Faculty Profiles - MA Jian Feng

Papers - MA Jian Feng

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Introduction of Third Silicon in Agriculture Conference

Ma Jian Feng

Japanese Journal of Soil Science and Plant Nutrition 77 ( 2 ) 243 - 243 2006

3. Application of Proteomics to the Study of Plant Mineral Stress(Impact of Genomics on the Study of Plant Nutrition)

Furukawa Jun, Ma Jian Feng

Japanese Journal of Soil Science and Plant Nutrition 77 ( 1 ) 109 - 114 2006

Physiological mechanisms of at resistance in higher plants

JF Ma

SOIL SCIENCE AND PLANT NUTRITION 51 ( 5 ) 609 - 612 2005.9

Language：English Publishing type：Research paper (international conference proceedings) Publisher：JAPANESE SOC SOIL SCIENCE PLANT NUTRITION

Aluminum (Al) ion is toxic to plant growth, while the resistance to Al toxicity varies widely among plant species. Accumulating evidence has shown that organic acids play an important role in both internal and external detoxification of Al. Two patterns of Al-induced secretion of organic acid anions have been characterized in the external detoxification. Involvement of ABA or protein phosphorylation in the activation of anion channel in Pattern I and less contribution of organic acid metabolism in Pattern 11 have been reported. Recently, gene or quantitative trait locus (QTL) for Al-activated secretion of organic acid anions has been identified. Other mechanisms of Al resistance are also reported such as pH increase in the rhizosphere. The formation of a non-toxic Al complex with organic acids or other chelators and sequestering these complexes in the vacuoles play an important role in internal detoxification of Al in Al-accumulating plants.

DOI： 10.1111/j.1747-0765.2005.tb00074.x

Identification of the form of Cd in the leaves of a superior Cd-accumulating ecotype of Thlaspi caerulescens using Cd-113-NMR

D Ueno, JF Ma, T Iwashita, FJ Zhao, SP McGrath

PLANTA 221 ( 6 ) 928 - 936 2005.8

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

Thlaspi caerulescens (Ganges ecotype) is a known Cd hyperaccumulator, however, the ligands which coordinate to Cd ions in the leaves have not been identified. In the present study, the chemical form of Cd was investigated by using (113)supercript stopCd-nuclear magnetic resonance (NMR) spectroscopy. Plants were grown hydroponically with a highly enriched (113)supercript stopCd stable isotope. Measurements of (113)supercript stopCd-NMR with intact leaves showed a signal at the chemical shift of around -16 ppm. Crude leaf sap also gave a similar chemical shift. Purification by gel filtration (Sephadex G-10), followed by cationic and anionic exchange chromatography, showed that Cd occurred only in the anionic fraction, which gave the same chemical shift as intact leaves. Further purification of the anionic fraction, combined with (113)supercript stopCd- and (1)supercript stopH-NMR studies, revealed that only the fraction containing malate showed a chemical shift similar to the intact leaves. These results indicate that Cd was coordinated mainly with malate in the leaves of T. caerulescens. The malate concentration in the leaves was not affected by increasing Cd concentration in the solution, suggesting that malate synthesis is not induced by Cd. Because the Cd-malate complex is relatively weak, we suggest that the complex forms inside the vacuoles as a result of an efficient tonoplast transport of Cd and a constitutively high concentration of malate in the vacuoles, and that the formation of the Cd-malate complex may lead to a decrease of subsequent Cd efflux to the cytoplasm.

DOI： 10.1007/s00425-005-1491-y

Isolation and characterization of a rice mutant hypersensitive to Al

JF Ma, S Nagao, CF Huang, M Nishimura

PLANT AND CELL PHYSIOLOGY 46 ( 7 ) 1054 - 1061 2005.7

Language：English Publishing type：Research paper (scientific journal) Publisher：OXFORD UNIV PRESS

Rice (Oryza sativa L.) is a highly Al-resistant species among small grain crops, but the mechanism responsible for the high Al resistance has not been elucidated. In this study, rice mutants sensitive to Al were isolated from M-3 lines derived from an Al-resistant cultivar, Koshihikari, irradiated with gamma-rays. Relative root elongation was used as a parameter for evaluating Al resistance. After initial screening plus two rounds of confirmatory testing, a mutant (als1) was isolated from a total of 560 lines. This mutant showed a phenotype similar to the wild-type plant in the absence of Al. However, in the presence of 10 mu M Al, root elongation was inhibited 70% in the mutant, but only 8% in the wild-type plant. The mutant also showed poorer root growth in acid soil. The Al content of root apices (0-1 cm) was much lower in the wild-type plant. The sensitivity to other metals including Cd and La did not differ between the mutant and the wild-type plants. A small amount of citrate was secreted from the roots of the mutant in response to Al stress, but there was no difference from that secreted by the wild-type plant. Genetic analysis of F-2 populations between als1 and wild-type plants showed that the Al-resistant seedlings and Al-sensitive seedlings segregated at a 3 : 1 ratio, indicating that the high sensitivity to Al in als1 is controlled by a single recessive gene. The gene was mapped to the long arm of chromosome 6, flanked by InDel markers MaOs0619 and MaOs0615.

DOI： 10.1093/pcp/pci116

Uptake system of silicon in different plant species

N Mitani, JF Ma

JOURNAL OF EXPERIMENTAL BOTANY 56 ( 414 ) 1255 - 1261 2005.4

Language：English Publishing type：Research paper (scientific journal) Publisher：OXFORD UNIV PRESS

The accumulation of silicon (Si) in the shoots varies considerably among plant species, but the mechanism responsible for this variation is poorly understood. The uptake system of Si was investigated in terms of the radial transport from the external solution to the root cortical cells and the release of Si from the cortical cells to the xylem in rice, cucumber, and tomato, which differ greatly in shoot Si concentration. Symplasmic solutions of the root tips were extracted by centrifugation. The concentrations of Si in the root-cell symplast in all species were higher than that in the external solution, although the concentration in rice was 3- and 5-fold higher than that in cucumber and tomato, respectively. A kinetic study showed that the radial transport of Si was mediated by a transporter with a K-m value of 0.15 mM in all species, but with different V-max values in the order of rice > cucumber > tomato. In the presence of the metabolic inhibitor 2,4-dinitrophenol, and at low temperature, the Si concentration in the root-cell symplast decreased to a level similar to that of the apoplasmic solution. These results suggest that both transporter-mediated transport and passive diffusion of Si are involved in the radial transport of Si and that the transporter-mediated transport is an energy-dependent process. The Si concentration of xylem sap in rice was 20- and 100-fold higher than that in cucumber and tomato, respectively. In contrast to rice, the Si concentration in the xylem sap was lower than that in the external solution in cucumber and tomato. A kinetic study showed that xylem loading of Si was also mediated by a kind of transporter in rice, but by passive diffusion in cucumber and tomato. These results indicate that a higher density of transporter for radial transport and the presence of a transporter for xylem loading are responsible for the high Si accumulation in rice.

DOI： 10.1093/jxb/eri121

Subcellular localisation of Cd and Zn in the leaves of a Cd-hyperaccumulating ecotype of Thlaspi caerulescens

JF Ma, D Ueno, FJ Zhao, SP McGrath

PLANTA 220 ( 5 ) 731 - 736 2005.3

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

Thlaspi caerulescens (Ganges ecotype) is able to accumulate large concentrations of cadmium (Cd) and zinc (Zn) in the leaves without showing any toxicity, suggesting a strong internal detoxification. The distribution of Cd and Zn in the leaves was investigated in the present study. Although the Cd and Zn concentrations in the epidermal tissues were 2-fold higher than those of mesophyll tissues, 65-70% of total leaf Cd and Zn were distributed in the mesophyll tissues, suggesting that mesophyll is a major storage site of the two metals in the leaves. To examine the subcellular localisation of Cd and Zn in mesophyll tissues, protoplasts and vacuoles were isolated from plants exposed to 50 muM Cd and Zn hydroponically. Pure protoplasts and vacuoles were obtained based on light-microscopic observation and the activities of marker enzymes of cytosol and vacuoles. Of the total Cd and Zn in the mesophyll tissues, 91% and 77%, respectively, were present in the protoplast, and all Cd and 91% Zn in the protoplast were localised in the vacuoles. Furthermore, about 70% and 86% of total Cd and Zn, respectively, in the leaves were extracted in the cell sap, suggesting that most Cd and Zn in the leaves is present in soluble form. These results indicate that internal detoxification of Cd and Zn in Thlaspi caerulescens leaves is achieved by vacuolar compartmentalisation.

DOI： 10.1007/s00425-004-1392-5

Identification of the silicon form in xylem sap of rice (Oryza sativa L.)

N Mitani, JF Ma, T Iwashita

PLANT AND CELL PHYSIOLOGY 46 ( 2 ) 279 - 283 2005.2

Language：English Publishing type：Research paper (scientific journal) Publisher：OXFORD UNIV PRESS

Rice (Oryza sativa L.) is a typical silicon (Si)-accumulating plant, but the mechanism responsible for the translocation from the root to the shoot is poorly understood. In this study, the form of Si in xylem sap was identified by 2 Si-29-nuclear magnetic resonance (NMR) spectroscopy. In rice (cv. Oochikara) cultured in a monosilicic acid solution containing 0.5 mM Si, the Si concentration in the xylem reached 6 mM,l within 30 min. In the Si-29-NMR spectra of the xylem sap, only one signal was observed at a chemical shift of -72.6 ppm, which is consistent with that of monosilicic acid. A H-1-NMR study of xylem sap did not show any significant difference between the wild-type rice and mutant rice defective in Si uptake, and the components of the xylem sap were not affected by the Si supply. The Si concentration in the xylem sap in vitro decreased from an initial 18 mM to 2.6 mM with time. Addition of xylem sap to a solution containing 8 mM Si did not prevent the polymerization of silicic acid. All these results indicate that Si is translocated in the form of monosilicic acid through the xylem and that the concentration of monosilicic acid is high in the xylem only transiently.

DOI： 10.1093/pcp/pci018

Isolation and characterization of Lsi1 Reviewed

N Mitani, K Tamai, S Konishi, M Yano, N Yamaji, M Kyo, JF Ma

PLANT AND CELL PHYSIOLOGY 46 S82 - S82 2005

Plant root responses to three abundant soil minerals: Silicon, aluminum and iron

JF Ma

CRITICAL REVIEWS IN PLANT SCIENCES 24 ( 4 ) 267 - 281 2005

Language：English Publisher：TAYLOR & FRANCIS INC

Silicon (Si), aluminum (Al), and iron (Fe) are the three most abundant minerals in soil; however, their effects on plants differ because they are beneficial, toxic, and essential to plant growth, respectively. High accumulation of silicon in the shoots helps some plants to overcome a range of biotic and abiotic stresses. However, plants vary in their ability to take up Si from the soil and load it into the xylem and so the accumulation of silicon varies greatly between plant species. Aluminum toxicity is characterized by a rapid inhibition of root elongation but some species and even genotypes within species can tolerate Al toxicity better than others. While the mechanisms controlling this tolerance in most of the more resistant species are poorly understood, some plants are able to detoxify Al externally and/or internally by complexation with ligands or by pH changes in the rhizosphere. Iron is taken up from the soil by two efficient mechanisms called Strategy I and Strategy II, which operate in distinct phylogenic groups. Strategy I plants increase soil Fe solubility by releasing protons and reductants/chelators, such as organic acids and phenolics, into the rhizosphere, while Strategy II plants are characterized by the secretion of ferric chelating substances (phytosiderophores) coupled with a specific Fe3+ :chelate uptake system. In this review, the molecular mechanisms underlying root response to Si, Al, and Fe are described.

DOI： 10.1080/07352680500196017

Genotypic variation in Fe concentration of barley grain

JF Ma, A Higashitani, K Sato, K Takeda

SOIL SCIENCE AND PLANT NUTRITION 50 ( 7 ) 1115 - 1117 2004.12

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

Iron deficiency in humans is the most prevalent micronutrient deficiency worldwide. To screen for high Fe cultivar, genotypic variation in Fe concentration of barley grain was investigated in two collections of barley: 274 standard varieties selected at the Barley Germplasm Center of the Research Institute for Bioresources, Okayama University (SV) and 135 varieties from the Barley Core Collection of Americas (BCCAM). The Fe concentration of barley grain showed large variation, ranging from 24.6 to 63.3 mg kg(-1) in SV, from 21.0 to 83.0 mg kg(-1) in BCCAM barleys. The Fe concentration was not affected by the key characters of barley varieties, kernel row types, and hulled or hull-less. The Fe concentration was also not related to the place of origin of the barley variety. About 90% of total Fe was localized in the grain without hull. These results provide fundamental data for breeding Fe-rich cultivars and for studying the mechanisms involved in genotypic variation in Fe concentration.

DOI： 10.1080/00380768.2004.10408583

Characterization of the silicon uptake system and molecular mapping of the silicon transporter gene in rice

JF Ma, N Mitani, S Nagao, S Konishi, K Tamai, T Iwashita, M Yano

PLANT PHYSIOLOGY 136 ( 2 ) 3284 - 3289 2004.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER SOC PLANT BIOLOGISTS

Rice (Oryza sativa L. cv Oochikara) is a typical silicon-accumulating plant, but the mechanism responsible for the high silicon uptake by the roots is poorly understood. We characterized the silicon uptake system in rice roots by using a low-silicon rice mutant (Isi1) and wild-type rice. A kinetic study showed that the concentration of silicon in the root symplastic solution increased with increasing silicon concentrations in the external solution but saturated at a higher concentration in both lines. There were no differences in the silicon concentration of the symplastic solution between the wild-type rice and the mutant. The form of soluble silicon in the root, xylem, and leaf identified by Si-29-NMR was also the same in the two lines. However, the concentration of silicon in the xylem sap was much higher in the wild type than in the mutant. These results indicate that at least two transporters are involved in silicon transport from the external solution to the xylem and that the low-silicon rice mutant is defective in loading silicon into xylem rather than silicon uptake from external solution to cortical cells. To map the responsible gene, we performed a bulked segregant analysis by using both microsatellite and expressed sequence tag-based PCR markers. As a result, the gene was mapped to chromosome 2, flanked by microsatellite marker RM5303 and expressed sequence tag-based PCR marker E60168.

DOI： 10.1104/pp.104.047365

Cadmium and zinc accumulation by the hyperaccumulator Thlaspi caerulescens from soils enriched with insoluble metal compounds

D Ueno, FJ Zhao, RF Shen, JF Ma

SOIL SCIENCE AND PLANT NUTRITION 50 ( 4 ) 511 - 515 2004.8

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPANESE SOC SOIL SCIENCE PLANT NUTRITION

Thlaspi caerulescens J. & C. Presl is a hyperaccumulator of both Zn and Cd. A pot experiment was carried out to investigate whether T caerulescens (the Ganges ecotype) could utilize Cd and Zn from insoluble sources. An uncontaminated soil was enriched with either insoluble Cd compounds (CdS or CdCO3), or soluble Cd (CdSO4) at a rate of 56 mg Cd kg(-1) soil. In a separate experiment, soil was enriched with either ZnSO4, Zn-3(PO4)(2), or ZnS at a rate of 100 mg Zn kg(-1). Neither soluble nor insoluble forms of Cd or Zn affected the growth of T caerulescens. The Cd concentration of the shoots of the plants grown on the unenriched soil was 40 mg kg(-1) dry wt., whereas the concentration in the case of the enriched soil reached 2,050 to 2,900 mg kg(-1) dry wt. However, there were no significant differences in the shoot Cd concentration between the treatments with soluble or insoluble Cd compounds, even though the Cd concentration in the soil solution was in the order of CdSO4 much greater thanCdC03 > CdS. T caerulescens grown on the ZnS-enriched soil accumulated up to 6,900 mg kg(-1) Zn in the shoots, although Zn accumulation was 1.5-fold higher with the addition of the more soluble compounds Zn-3(PO4)(2) or ZnSO4. These results indicate that the Ganges ecotype of T caerulescens is able to utilize both insoluble Cd and Zn compounds.

DOI： 10.1080/00380768.2004.10408507

Interactions between Cd and Zn in relation to their hyperaccumulation in Thlaspi caerulescens

D Ueno, FJ Zhao, JF Ma

SOIL SCIENCE AND PLANT NUTRITION 50 ( 4 ) 591 - 597 2004.8

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPANESE SOC SOIL SCIENCE PLANT NUTRITION

Ganges, an ecotype of Thlaspi caerulescens from southern France accumulates both Zn and Cd to extraordinary levels in the shoots. The interactions between Zn and Cd in this ecotype were investigated using solution culture and pot experiments with soil. Results from both relatively long-term (4 weeks) and short-term (1 week) solution culture experiments indicated that Cd accumulation in the shoots was not affected by the supply of a 4 to 10-fold excess of Zn, whereas the Cd concentration of the roots decreased with increasing Zn concentration in the solution. By contrast, the supply of an equimolar concentration of Cd significantly reduced the Zn concentration in both roots and shoots. However, when 4-fold more Zn than Cd was supplied, Cd-induced decrease in Zn accumulation was not observed. In soil treated with Cd or Zn, addition of one metal increased the metal concentration of the other in the soil solution. However, Zn accumulation by T caerulescens decreased by Cd addition, whereas Cd accumulation was not affected by Zn addition. These results suggested that the Ganges ecotype of T. caerulescens displayed different uptake systems for Cd and Zn, and that Cd competed with Zn uptake while Zn did not compete with Cd uptake.

DOI： 10.1080/00380768.2004.10408516

Molecular mapping of a gene responsible for Al-activated secretion of citrate in barley. International journal

Jian Feng Ma, Sakiko Nagao, Kazuhiro Sato, Hiroyuki Ito, Jun Furukawa, Kazuyoshi Takeda

Journal of experimental botany 55 ( 401 ) 1335 - 41 2004.6

Language：English Publishing type：Research paper (scientific journal)

Aluminium (Al) toxicity is an important limitation to barley (Hordeum vulgare L.) on acid soil. Al-resistant cultivars of barley detoxify Al externally by secreting citrate from the roots. To link the genetics and physiology of Al resistance in barley, genes controlling Al resistance and Al-activated secretion of citrate were mapped. An analysis of Al-induced root growth inhibition from 100 F2 seedlings derived from an Al-resistant cultivar (Murasakimochi) and an Al-sensitive cultivar (Morex) showed that a gene associated with Al resistance is localized on chromosome 4H, tightly linked to microsatellite marker Bmag353. Quantitative trait locus (QTL) analysis from 59 F4 seedlings derived from an F3 plant heterozygous at the region of Al resistance on chromosome 4H showed that a gene responsible for the Al-activated secretion of citrate was also tightly linked to microsatellite marker Bmag353. This QTL explained more than 50% of the phenotypic variation in citrate secretion in this population. These results indicate that the gene controlling Al resistance on barley chromosome 4H is identical to that for Al-activated secretion of citrate and that the secretion of citrate is one of the mechanisms of Al resistance in barley. The identification of the microsatellite marker associated with both Al resistance and citrate secretion provides a valuable tool for marker-assisted selection of Al-resistant lines.

DOI： 10.1093/jxb/erh152

Role of silicon in enhancing the resistance of plants to biotic and abiotic stresses

JF Ma

SOIL SCIENCE AND PLANT NUTRITION 50 ( 1 ) 11 - 18 2004.2

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPANESE SOC SOIL SCIENCE PLANT NUTRITION

Although silicon (Si) has not been recognized as an essential element for plant growth, the beneficial effects of Si have been observed in a wide variety of plant species. The beneficial effects of Si are usually expressed more clearly in Si-accumulating plants under various abiotic and biotic stress conditions. Silicon is effective in controlling various pests and diseases caused by both fungi and bacteria in different plant species. Silicon also exerts alleviative effects on various abiotic stresses including salt stress, metal toxicity, drought stress, radiation damage, nutrient imbalance, high temperature, freezing and so on. These beneficial effects are mainly attributed to the high accumulation of silica on the tissue surface although other mechanisms have also been proposed. To obtain plants resistant to multiple stresses, genetic modification of the root ability to take up Si has been proposed. In this review, the role of Si in conferring resistance to mutiple stresses is described.

DOI： 10.1080/00380768.2004.10408447

Form of Al changes with Al concentration in leaves of buckwheat

RF Shen, T Iwashita, JF Ma

JOURNAL OF EXPERIMENTAL BOTANY 55 ( 394 ) 131 - 136 2004.1

Language：English Publishing type：Research paper (scientific journal) Publisher：OXFORD UNIV PRESS

Buckwheat (Fagopyrum esculentum Moench. cv. Jianxi) is known as an Al-accumulating plant. The process leading to the accumulation of Al in the leaves was investigated, focusing on the chemical form of Al using Al-27-nuclear magnetic resonance. Leaves with different Al concentrations were prepared by growing buckwheat on a very acidic soil (Andosol) amended with or without CaCO3 (1 or 3 g kg(-1) soil). When the Al concentration of the leaves was lower, only one major signal was observed at a chemical shift of 16.1 ppm, which was assigned to an Al-oxalate complex at a 1:3 ratio. However, when the Al concentration of the leaves increased to a high level (e.g. 12 g Al kg(-1)), an additional signal at a chemical shift of 11.2 ppm was observed. This signal was assigned to an Al-citrate complex at a 1:1 ratio. In the leaf with a high Al concentration, both Al-oxalate (1:3) and Al-citrate (1:1) were detected in marginal and middle parts, while only Al-oxalate was detected in the basal part. The oxalate concentration did not differ very much between leaves with low and high Al concentrations at the same position, while citrate concentration significantly increased with increasing Al concentration when the oxalate/Al ratio became lower than 3.0. As the Al-citrate complex has been demonstrated to be the form of transport in the xylem, the results suggest that when internal oxalate is enough to form a complex with Al at a 3:1 ratio in the leaves with a low Al concentration, Al-citrate converts to Al-oxalate. However, this conversion does not occur in the leaves with a very high Al concentration, resulting in the coexistence of both Al-oxalate and Al-citrate complexes.

DOI： 10.1093/jxb/erh016

Aluminum targets elongating cells by reducing cell wall extensibility in wheat roots

JF Ma, RF Shen, S Nagao, E Tanimoto

PLANT AND CELL PHYSIOLOGY 45 ( 5 ) 583 - 589 2004

Language：English Publishing type：Research paper (scientific journal) Publisher：OXFORD UNIV PRESS

Phytotoxicity of aluminum is characterized by a rapid inhibition of root elongation at micromolar concentrations, however, the mechanisms primarily responsible for this response are not well understood. We investigated the effect of Al on the viscosity and elasticity parameters of root cell wall by a creep-extension analysis in two cultivars of wheat (Triticum aestivum L.) differing in Al resistance. The root elongation and both viscous and elastic extensibility of cell wall of the root apices were hardly affected by the exposure to 10 muM Al in an Al-resistant cultivar, Atlas 66. However, similar exposure rapidly inhibited root elongation in an Al-sensitive cultivar, Scout 66 and this was associated with a time-dependent accumulation of Al in the root tissues with more than 77% residing in the cell wall. Al caused a significant decrease in both the viscous and elastic extensibility of cell wall of the root apices of Scout 66. The "break load" of the root apex of Scout 66 was also decreased by Al. However, neither the viscosity nor elasticity of the cell wall was affected by in vitro Al treatment. Furthermore, pre-treatment of seedlings with Al in conditions where root elongation was slow (i.e. low temperature) did not affect the subsequent elongation of roots in a 0 Al treatment at room temperature. These results suggest that the Al-dependent changes in the cell wall viscosity and elasticity are involved in the inhibition of root growth. Furthermore, for Al to reduce cell wall extensibility it must interact with the cell walls of actively elongating cells.

DOI： 10.1093/pcp/pch060

Announcement of XV International Plant Nutrition Colloquium

Ma Jian Feng

Japanese Journal of Soil Science and Plant Nutrition 75 ( 4 ) 535 - 535 2004

Recent progress in the research of external Al detoxification in higher plants: a minireview

JF Ma, J Furukawa

JOURNAL OF INORGANIC BIOCHEMISTRY 97 ( 1 ) 46 - 51 2003.9

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ELSEVIER SCIENCE INC

Aluminum (Al) is highly toxic to plant growth. The toxicity is characterized by rapid inhibition of root elongation. However, some plant species and cultivars have evolved some mechanisms for detoxifying Al both internally and externally. In this review, the recent progress made in the research of external detoxification of Al is described. Accumulating evidence has shown that organic acids play an important role in the detoxification of Al. Some plant species and cultivars respond to Al by secreting citrate, malate or oxalate from the roots. Recently, the anion channel of malate and citrate in the plasma membrane has been characterized and a gene encoding the malate channel has been cloned. The metabolism of organic acids seems to be poorly correlated with the Al-induced secretion of organic acid anions. A number of QTLs (quantitative trait loci) for Al resistance have been identified in rice, Arabidopsis, and other species. Transgenic plants with enhanced resistance to Al have also been reported, but introduction of multiple genes may be required to gain high Al resistance in future. (C) 2003 Published by Elsevier Inc.

DOI： 10.1016/S0162-0134(03)00245-9

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