Faculty Profiles - MA Jian Feng

Papers - MA Jian Feng

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Differential gene expression of rice in response to silicon and rice blast fungus Magnaporthe oryzae

A. M. Brunings, L. E. Datnoff, J. F. Ma, N. Mitani, Y. Nagamura, B. Rathinasabapathi, M. Kirst

ANNALS OF APPLIED BIOLOGY 155 ( 2 ) 161 - 170 2009

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

Silicon increases the resistance of rice (Oryza sativa) to the rice blast pathogen Magnaporthe oryzae. This study described the relationship between silicon and M. oryzae in terms of whole-genome gene expression. By assessing gene expression patterns in the rice cultivar Monko-to using microarray technology, the physiological basis for silicon-induced resistance was investigated. Silicon amendment resulted in the differential regulation of 221 genes in rice without being challenged with the pathogen. This means that silicon had an observable effect on rice metabolism, as opposed to playing a simple passive role in the resistance response of rice. Compared with control plants, silicon-amended rice differentially regulated 60% less genes, implying that silicon affects the rice response to rice blast infection at a transcriptional level.

DOI： 10.1111/j.1744-7348.2009.00347.x

Specific transporter for iron(III)-phytosiderophore complex involved in iron uptake by barley roots

Yoshiko Murata, Emiko Harada, Kenji Sugase, Kosuke Namba, Manabu Horikawa, Jian Feng Ma, Naoki Yamaji, Daisei Ueno, Kyosuke Nomoto, Takashi Iwashita, Shoichi Kusumoto

PURE AND APPLIED CHEMISTRY 80 ( 12 ) 2689 - 2697 2008.12

Language：English Publishing type：Research paper (international conference proceedings) Publisher：INT UNION PURE APPLIED CHEMISTRY

Iron (Fe) is an essential element for plant growth. Gramineous plants have generally developed a distinct strategy to efficiently acquire insoluble Fe, which is characterized by the synthesis and secretion of an Fe-chelating substance, phytosiderophore (PS) such as mugineic acid (MA), and by a specific uptake system for Fe(III)-PS complexes. In a previous study, we identified a gene specifically encoding an Fe(III)-PS transporter (HvYS1) in barley. This gene as well as the encoded protein is specifically expressed in the epidermal cells of the roots, and gene expression is greatly enhanced under Fe-deficient conditions. The localization and substrate specificity of HvYS1 indicate that it is a Fe(III)-PS specific transporter in barley roots. In contrast, ZmYS1, which has been reported as ail Fe-PS transporter from maize, possesses broad substrate specificity despite a high homology with HvYS1. By assessing the transport activity of a series of HvYS1-ZmYS1 chimeras, we revealed that the outer membrane loop between the 6(th) and 7(th) transmembrane regions is essential for the substrate specificity. We also achieved an efficient short-step synthesis of MA and 2'-deoxymugineic acid (DMA). Our new synthetic method enabled us to use them in a large quantity for biological studies.

DOI： 10.1351/pac200880122689

Functions and transport of silicon in plants

J. F. Ma, N. Yamaji

CELLULAR AND MOLECULAR LIFE SCIENCES 65 ( 19 ) 3049 - 3057 2008.10

Language：English Publisher：BIRKHAUSER VERLAG AG

Silicon exerts beneficial effects on plant growth and production by alleviating both biotic and abiotic stresses including diseases, pests, lodging, drought, and nutrient imbalance. Recently, two genes (Lsi1 and Lsi2) encoding Si transporters have been identified from rice. Lsi1 (low silicon 1) belongs to a Nod26-like major intrinsic protein subfamily in aquaporin, while Lsi2 encodes a putative anion transporter. Lsi1 is localized on the distal side of both exodermis and endodermis in rice roots, while Lsi2 is localized on the proximal side of the same cells. Lsi1 shows influx transport activity for Si, while Lsi2 shows efflux transport activity. Therefore, Lsi1 is responsible for transport of Si from the external solution to the root cells, whereas Lsi2 is an efflux transporter responsible for the transport of Si from the root cells to the apoplast. Coupling of Lsi1 with Lsi2 is required for efficient uptake of Si in rice.

DOI： 10.1007/s00018-008-7580-x

Transporters of arsenite in rice and their role in arsenic accumulation in rice grain

Jian Feng Ma, Naoki Yamaji, Namiki Mitani, Xiao-Yan Xu, Yu-Hong Su, Steve P. McGrath, Fang-Jie Zhao

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 105 ( 29 ) 9931 - 9935 2008.7

Language：English Publishing type：Research paper (scientific journal) Publisher：NATL ACAD SCIENCES

Arsenic poisoning affects millions of people worldwide. Human arsenic intake from rice consumption can be substantial because rice is particularly efficient in assimilating arsenic from paddy soils, although the mechanism has not been elucidated. Here we report that two different types of transporters mediate transport of arsenite, the predominant form of arsenic in paddy soil, from the external medium to the xylem. Transporters belonging to the NIP subfamily of aquaporins in rice are permeable to arsenite but not to arsenate. Mutation in OsNIP2;1 (Lsi1, a silicon influx transporter) significantly decreases arsenite uptake. Furthermore, in the rice mutants defective in the silicon efflux transporter Lsi2, arsenite transport to the xylem and accumulation in shoots and grain decreased greatly. Mutation in Lsi2 had a much greater impact on arsenic accumulation in shoots and grain in field-grown rice than Lsi1. Arsenite transport in rice roots therefore shares the same highly efficient pathway as silicon, which explains why rice is efficient in arsenic accumulation. Our results provide insight into the uptake mechanism of arsenite in rice and strategies for reducing arsenic accumulation in grain for enhanced food safety.

DOI： 10.1073/pnas.0802361105

Characterization of substrate specificity of a rice silicon transporter, Lsi1

Namiki Mitani, Naoki Yamaji, Jian Feng Ma

PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY 456 ( 4 ) 679 - 686 2008.7

Language：English Publisher：SPRINGER HEIDELBERG

Lsi1 (OsNIP2;1) is the first silicon (silicic acid) transporter identified in plant, which belongs to the nodulin 26-like intrinsic membrane protein (NIP) subfamily. In this study, we characterized the function of this transporter by using the Xenopus laevis oocyte expression system. The transport activity of Lsi1 for silicic acid was significantly inhibited by HgCl2 but not by low temperature. Lsi1 also showed an efflux transport activity for silicic acid. The substrate specificity study showed that Lsi1 was able to transport urea and boric acid; however, the transport activity for silicic acid was not affected by the presence of equimolar urea and was decreased only slightly by boric acid. Furthermore, among the NIPs subgroup, OsNIP2;2 showed transport activity for silicic acid, whereas OsNIP1;1 and OsNIP3;1 did not. We propose that Lsi1 and its close homologues form a unique subgroup of NIP with a distinct ar/R selectivity filter, which is located in the narrowest region on the extra-membrane mouth and govern the substrate specificity of the pore.

DOI： 10.1007/s00424-007-0408-y

Transcriptome analysis of the silicon-Magnaporthe grisea interaction

A. M. Brunings, L. E. Datnoff, J. F. Ma, N. Mitani, Y. Nagamura, B. Rathinasabapathi

PHYTOPATHOLOGY 98 ( 6 ) S28 - S28 2008.6

Reexamination of silicon effects on rice growth and production under field conditions using a low silicon mutant

Kazunori Tamai, Jian Feng Ma

PLANT AND SOIL 307 ( 1-2 ) 21 - 27 2008.6

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

Silicon (Si) is a beneficial element for healthy growth and high and sustainable production of rice, but the mode of action of the beneficial effects has not been well understood. We carried out field trials for four years at two different locations to re-examine the effects of Si on the growth and production of rice using a low silicon rice (lsi1) mutant. The mutant accumulated much lower Si at each growth stage compared with the wild-type rice (Oryza sativa L. cv Oochikara), but there was no difference in the accumulation of other nutrients including N, P, and K. Measurements at different growth stages showed that low Si in the mutant hardly affected the tiller number, chlorophyll content (SPAD value), and root growth. The plant height and shoot dry weight of the wild-type rice were slightly higher than those of the mutant at a later growth stage, but the difference was not significant between the two lines. However, grain yield was reduced by 79-98%, depending on year, due to a low Si accumulation in the mutant, which showed the largest effect of Si on rice production among all studies reported so far. Among the yield components, the percentage of filled spikelets was mostly affected, being only 13.9% of the wild-type rice in the mutant. The grain color of the mutant became brown because of excessive transpiration and infection of pathogens. These results indicate that Si increases rice yield mainly by enhancing the fertility of spikelets.

DOI： 10.1007/s11104-008-9571-y

A transporter regulating silicon distribution in rice shoots

Naoki Yamaji, Namiki Mitatni, Jian Feng Ma

PLANT CELL 20 ( 5 ) 1381 - 1389 2008.5

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

Rice (Oryza sativa) accumulates very high concentrations of silicon (Si) in the shoots, and the deposition of Si as amorphous silica helps plants to overcome biotic and abiotic stresses. Here, we describe a transporter, Lsi6, which is involved in the distribution of Si in the shoots. Lsi6 belongs to the nodulin-26 intrinsic protein III subgroup of aquaporins and is permeable to silicic acid. Lsi6 is expressed in the leaf sheath and leaf blades as well as in the root tips. Cellular localization studies revealed that Lsi6 is found in the xylem parenchyma cells of the leaf sheath and leaf blades. Moreover, Lsi6 showed polar localization at the side facing toward the vessel. Knockdown of Lsi6 did not affect the uptake of Si by the roots but resulted in disordered deposition of silica in the shoots and increased excretion of Si in the guttation fluid. These results indicate that Lsi6 is a transporter responsible for the transport of Si out of the xylem and subsequently affects the distribution of Si in the leaf.

DOI： 10.1105/tpc.108.059311

Characterization of Cd translocation and identification of the Cd form in xylem sap of the Cd-hyperaccumulator Arabidopsis halleri

Daisei Ueno, Takashi Iwashita, Fang-Jie Zhao, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 49 ( 4 ) 540 - 548 2008.4

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

Arabidopsis halleriis a Cd hyperaccumulator; however, the mechanisms involved in the root to shoot translocation of Cd are not well understood. In this study, we characterized Cd transfer from the root medium to xylem in this species. Arabidopsis halleri accumulated 1,500 mg kg(1) Cd in the shoot without growth inhibition. A time-course experiment showed that the release of Cd into the xylem was very rapid; by 2 h exposure to Cd, Cd concentration in the xylem sap was 5-fold higher than that in the external solution. The concentration of Cd in the xylem sap increased linearly with increasing Cd concentration in the external solution. Cd transfer to the xylem was completely inhibited by the metabolic inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Cd concentration in the xylem sap was decreased by increasing the concentration of external Zn, but enhanced by Fe deficiency treatment. Analysis with (113)Cd-nuclear magnetic resonance (NMR) showed that the chemical shift of (113)Cd in the xylem sap was the same as that of Cd(NO(3))(2). Metal speciation with Geochem-PC also showed that Cd occurred mainly in the free ionic form in the xylem sap. These results suggest that Cd transfer from the root medium to the xylem in A. halleri is an energy-dependent process that is partly shared with Zn and/or Fe transport. Furthermore, Cd is translocated from roots to shoots in inorganic forms.

DOI： 10.1093/pcp/pcn026

Secretion of malate and citrate from roots is related to high Al-resistance in Lespedeza bicolor

Xiao Ying Dong, Ren Fang Shen, Rong Fu Chen, Zhao Liang Zhu, Jian Feng Ma

PLANT AND SOIL 306 ( 1-2 ) 139 - 147 2008.4

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPRINGER

Lespedeza bicolor (Lespedeza bicolor Turcz. cv. Jiangxi) is a leguminous shrub that is well adapted to acid infertile soils. However, the mechanisms of aluminum resistance in this species have not been established. This study aimed to assess the possible resistance mechanisms of this plant to Al. An Al-sensitive species of Lespedeza, sericea lespedeza [Lespedeza cuneata (Dum.-Cours.) G. Don cv. Zhejiang], was used as a reference. The roots of L. bicolor secreted both malate and citrate after exposure to Al, but roots of L. cuneata did not. The secretion of organic acids from L. bicolor was specific to Al; neither 15-day P starvation nor 50 mu M lanthanum induced the secretion of these organic acid anions. Secretion of organic acid anions in L. bicolor was detected after 3-6 h exposure to Al, and the amount increased significantly after 6 h exposure, suggesting that this plant shows a pattern II-type organic acid secretion. This is supported by the finding that the secretion was significantly inhibited by a protein-synthesis inhibitor, cycloheximide. Two kinds of anion-channel inhibitors had different effects on Al-induced secretion of organic acids: 9-anthracene carboxylic acid completely inhibited secretion, phenylglyoxal had no effect. Root elongation in L. bicolor was more severely inhibited by Al in the presence of 9-anthracene carboxylic acid. All these results indicated that the secretion of malate and citrate is a specialized response to Al stress in L. bicolor roots, which might be one of the Al-resistance mechanisms in this species.

DOI： 10.1007/s11104-008-9564-x

Uptake of Silicon in Different Plant Species

Jian Feng Ma

Handbook of Biomineralization: Biological Aspects and Structure Formation 1 113 - 124 2008.3

Publishing type：Part of collection (book)

Silicon (Si) is the second most abundant element in soil, and has a wide array of functions in the growth and development of plants. Silicon is able to alleviate various stresses including diseases, pests, lodging, drought, and nutrient imbalance. Although all plants contain some Si in their tissues, the concentrations of Si in the shoots differ greatly with plant species, and this difference is attributed to the capacity of the roots to take up Si. At least two steps are involved in Si uptake, including radial transport from external solution to the root cells, and subsequent release from the root cells to the xylem. Currently, the latter process seems more important for high Si accumulation. The first gene encoding Si transporter has recently been identified in rice, a typical Si-accumulating plant. The transporter encoded by this gene shows a high specificity for Si, and is localized at the distal side of both exodermis and endodermis. The future cloning of more genes will help in our understanding of the molecular mechanisms of Si uptake in different plant species. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/9783527619443.ch7

Variation in root-to-shoot translocation of cadmium and zinc among different accessions of the hyperaccumulators Thlaspi caerulescens and Thlaspi praecox

J. P. Xing, R. F. Jiang, D. Ueno, J. F. Ma, H. Schat, S. P. McGrath, F. J. Zhao

NEW PHYTOLOGIST 178 ( 2 ) 315 - 325 2008

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

Efficient root-to-shoot translocation is a key trait of the zinc/cadmium hyperaccumulators Thlaspi caerulescens and Thlaspi praecox, but the extent of variation among different accessions and the underlying mechanisms remain unclear.
Root-to-shoot translocation of Cd and Zn and apoplastic bypass flow were determined in 10 accessions of T. caerulescens and one of T. praecox, using radiolabels Cd-109 and Zn-65. Two contrasting accessions (Pr and Ga) of T. caerulescens were further characterized for TcHMA4 expression and metal compartmentation in roots.
Root-to-shoot translocation of Cd-109 and Zn-65 after 1 d exposure varied 4.4 to 5-fold among the 11 accessions, with a significant correlation between the two metals, but no significant correlation with uptake or the apoplastic bypass flow. The F-2 progeny from a cross between accessions from Prayon, Belgium (Pr) and Ganges, France (Ga) showed a continuous phenotype pattern and transgression. There was no significant difference in the TcHMA4 expression in roots between Pr and Ga. Compartmentation analysis showed a higher percentage of Cd-109 sequestered in the root vacuoles of Ga than Pr, the former being less efficient in translocation than the latter.
Substantial natural variation exists in the root-to-shoot translocation of Cd and Zn, and root vacuolar sequestration may be an important factor related to this variation.

DOI： 10.1111/j.1469-8137.2008.02376.x

The genetic basic and fine-mapping of a stable quantitative-trait loci for aluminium tolerance in rice

Y. Xue, L. Jiang, N. Su, J. K. Wang, P. Deng, J. F. Ma, H. Q. Zhai, J. M. Wan

PLANTA 227 ( 1 ) 255 - 262 2007.12

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

Aluminium (Al) toxicity is a primary cause of low rice productivity in acid soils. We have mapped a number of quantitative-trait loci (QTL) controlling Al tolerance in a recombinant inbred line population derived from a cross between the tolerant japonica cultivar Asominori and the sensitive indica cultivar IR24. Tolerance was assessed on the basis of relative root elongation. QTL were detected on chromosomes 1, 9, and 11, with the percentages of phenotypic variance explained ranging from 13.5 to 17.7%. Alleles from Asominori at all three QTL were associated with increased Al tolerance. qRRE-9 is expressed both in the genetic background of IR24 and in an Asominori/IR24-mixed background. qRRE-9 was reduced to the single recessive Mendelian factor Alt-9. High-resolution genetic and physical maps were constructed for Alt-9 in a BC3F2 population of 1,043 individuals. Alt-9 maps between RM24702 and ID47-2 on chromosome 9, and co-segregates with RM5765.

DOI： 10.1007/s00425-007-0613-0

Mutation in nicotianamine aminotransferase stimulated the Fe(II) acquisition system and led to iron accumulation in Rice

Longjun Cheng, Fang Wang, Huixia Shou, Fangliang Huang, Luqing Zheng, Fei He, Jinhui Li, Fang-Jie Zhao, Daisei Ueno, Jian Feng Ma, Ping Wu

PLANT PHYSIOLOGY 145 ( 4 ) 1647 - 1657 2007.12

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

Higher plants acquire iron (Fe) from the rhizosphere through two strategies. Strategy II, employed by graminaceous plants, involves secretion of phytosiderophores (eg. deoxymugineic acid in rice [Oryza sativa]) by roots to solubilize Fe(III) in soil. In addition to taking up Fe in the form of Fe(III)-phytosiderophore, rice also possesses the strategy I-like system that may absorb Fe(II) directly. Through mutant screening, we isolated a rice mutant that could not grow with Fe(III)-citrate as the sole Fe source, but was able to grow when Fe(II)-EDTA was supplied. Surprisingly, the mutant accumulated more Fe and other divalent metals in roots and shoots than the wild type when both were supplied with EDTA-Fe(II) or grown under waterlogged field conditions. Furthermore, the mutant had a significantly higher concentration of Fe in both unpolished and polished grains than the wild type. Using the map-based cloning method, we identified a point mutation in a gene encoding nicotianamine aminotransferase (NAAT1), which was responsible for the mutant phenotype. Because of the loss of function of NAAT1, the mutant failed to produce deoxymugineic acid and could not absorb Fe(III) efficiently. In contrast, nicotianamine, the substrate for NAAT1, accumulated markedly in roots and shoots of the mutant. Microarray analysis showed that the expression of a number of the genes involved in Fe(II) acquisition was greatly stimulated in the naat1 mutant. Our results demonstrate that disruption of deoxymugineic acid biosynthesis can stimulate Fe(II) acquisition and increase iron accumulation in rice.

DOI： 10.1104/pp.107.107912

Silicon transporters in rice

Jian Feng Ma, Naoki Yamaji, Namiki Mitani

Tanpakushitsu kakusan koso. Protein, nucleic acid, enzyme 52 ( 14 ) 1849 - 1856 2007.11

Genotypic difference in silicon uptake and expression of silicon transporter genes in rice

Jian Feng Ma, Naoki Yamaji, Kazunori Tamai, Namiki Mitani

PLANT PHYSIOLOGY 145 ( 3 ) 919 - 924 2007.11

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

Rice (Oryza sativa) is a highly silicon (Si)-accumulating species that shows genotypic differences in Si accumulation. We investigated the physiological and molecular mechanisms involved in the genotypic difference in Si uptake between the japonica var. Nipponbare and the indica var. Kasalath. Both the Si concentration in the shoot and the Si uptake per root dry weight were higher in Nipponbare than in Kasalath grown in either soil or nutrient solution. The Si uptake by a single root was also higher in Nipponbare than in Kasalath. A kinetics study showed that Nipponbare and Kasalath had a similar K-m value, whereas the V-max was higher in Nipponbare. The expression of two Si transporter genes (Low silicon rice 1 [Lsi1] and Lsi2) investigated using real-time reverse transcription polymerase chain reaction revealed higher expression of both genes in Nipponbare than in Kasalath. Immunostaining with Lsi1 and Lsi2 antibodies revealed a similar pattern of subcellular localization of these two Si transporters in both varieties; Lsi1 and Lsi2 were localized at the distal and proximal sides, respectively, of both exodermis and endodermis of the roots. These results revealed that the genotypic difference in the Si accumulation results from the difference in abundance of Si transporters in rice roots.

DOI： 10.1104/pp.107.107599

An aluminum-activated citrate transporter in barley

Jun Furukawa, Naoki Yamaji, Hua Wang, Namiki Mitani, Yoshiko Murata, Kazuhiro Sato, Maki Katsuhara, Kazuyoshi Takeda, Jian Feng Ma

PLANT AND CELL PHYSIOLOGY 48 ( 8 ) 1081 - 1091 2007.8

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

Soluble ionic aluminum (Al) inhibits root growth and reduces crop production on acid soils. Al-resistant cultivars of barley (Hordeum vulgare L.) detoxify Al by secreting citrate from the roots, but the responsible gene has not been identified yet. Here, we identified a gene (HvAACT1) responsible for the Al-activated citrate secretion by fine mapping combined with microarray analysis, using an Al-resistant cultivar, Murasakimochi, and an Al-sensitive cultivar, Morex. This gene belongs to the multidrug and toxic compound extrusion (MATE) family and was constitutively expressed mainly in the roots of the Al-resistant barley cultivar. Heterologous expression of HvAACTI in Xenopus oocytes showed efflux activity for 14 C-labeled citrate, but not for malate. Twoelectrode voltage clamp analysis also showed transport activity of citrate in the HvAACT1-expressing oocytes in the presence of Al. Overexpression of this gene in tobacco enhanced citrate secretion and Al resistance compared with the wild-type plants. Transiently expressed green fluorescent protein-tagged HvAACT1 was localized at the plasma membrane of the onion epidermal cells, and immunostaining showed that HvAACT1 was localized in the epidermal cells of the barley root tips. A good correlation was found between the expression of HvAACT1 and citrate secretion in 10 barley cultivars differing in Al resistance. Taken together, our results demonstrate that HvAACT1 is an Al-activated citrate transporter responsible for Al resistance in barley.

DOI： 10.1093/pcp/pcm091

An efflux transporter of silicon in rice

Jian Feng Ma, Naoki Yamaji, Namiki Mitani, Kazunori Tamai, Saeko Konishi, Toru Fujiwara, Maki Katsuhara, Masahiro Yano

NATURE 448 ( 7150 ) 209 - U12 2007.7

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Silicon is an important nutrient for the optimal growth and sustainable production of rice(1-4). Rice accumulates up to 10% silicon in the shoot, and this high accumulation is required to protect the plant from multiple abiotic and biotic stresses(1-5). A gene, Lsi1, that encodes a silicon influx transporter has been identified in rice(6). Here we describe a previously uncharacterized gene, low silicon rice 2 (Lsi2), which has no similarity to Lsi1. This gene is constitutively expressed in the roots. The protein encoded by this gene is localized, like Lsi1, on the plasma membrane of cells in both the exodermis and the endodermis, but in contrast to Lsi1, which is localized on the distal side, Lsi2 is localized on the proximal side of the same cells. Expression of Lsi2 in Xenopus oocytes did not result in influx transport activity for silicon, but preloading of the oocytes with silicon resulted in a release of silicon, indicating that Lsi2 is a silicon efflux transporter. The identification of this silicon transporter revealed a unique mechanism of nutrient transport in plants: having an influx transporter on one side and an efflux transporter on the other side of the cell to permit the effective transcellular transport of the nutrients.

DOI： 10.1038/nature05964

Sorghum roots are inefficient in uptake of EDTA-chelated lead

Yong Xu, Naoki Yamaji, Renfang Shen, Jian Feng Ma

ANNALS OF BOTANY 99 ( 5 ) 869 - 875 2007.5

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

Background and Aims Ethylene diamine tetraacetic acid (EDTA)-assisted phytoremediation has been developed to clean up lead (Pb)-contaminated soil; however, the mechanism responsible for the uptake of EDTA-Pb complex is not well understood. In this study, the accumulation process of Pb from EDTA-Pb is characterized in comparison to ionic Pb [Pb(NO3)(2)] in sorghum (Sorghum bicolor).Methods Sorghum seedlings were exposed to a 0.5 mm CaCl2 (pH 5.0) solution containing 0, 1 mm Pb(NO3)(2) or EDTA-Pb complexes at a molar ratio of 1:0.5, 1:1, 1:2 and 1:4 (Pb:EDTA). The root elongation of sorghum at different ratios of Pb:EDTA was measured. Xylem sap was collected after the stem was severed at different times. The concentration of Pb in the shoots and roots were determined by an atomic absorption spectrometer. In addition, the roots were stained with Fluostain I for observation of the root structure.Key Results Lead accumulation in the shoots of the plants exposed to EDTA-Pb at 1:1 ratio was only one-fifth of that exposed to ionic Pb at the same concentration. Lead accumulation decreased when transpiration was suppressed. The concentration of Pb in the xylem sap from the EDTA-Pb-treated plants was about 1/25 000 of that in the external solution. Root elongation was severely inhibited by ionic Pb, but not by EDTA-Pb at a 1:1 ratio. Root staining showed that a physiological barrier was damaged in the roots exposed to ionic Pb, but not in the roots exposed to EDTA-Pb.Conclusions All these results suggest that sorghum roots are inefficient in uptake of EDTA-chelated Pb and that enhanced Pb accumulation from ionic Pb was attributed to the damaged structure of the roots.

DOI： 10.1093/aob/mcm038

Spatial distribution and temporal variation of the rice silicon transporter Lsi1

Naoki Yamaji, Jian Feng Ma

PLANT PHYSIOLOGY 143 ( 3 ) 1306 - 1313 2007.3

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

Rice (Oryza sativa) is a typical silicon (Si) accumulator and requires a large amount of Si for high-yield production. Recently, a gene (Low silicon rice1 [Lsi1]) encoding a Si transporter was identified in rice roots. Here, we characterized Lsi1 in terms of spatial distribution and temporal variation using both physiological and molecular approaches. Results from a multicompartment transport box experiment showed that the major site for Si uptake was located at the basal zone (> 10 mm from the root tip) of the roots rather than at the root tips (< 10 mm from the root tip). Consistent with the Si uptake pattern, Lsi1 expression and distribution of the Lsi1 protein were found only in the basal zone of roots. In the basal zones of the seminal, crown, and lateral roots, the Lsi1 protein showed a polar localization at the distal side of both the exodermis and endodermis, where the Casparian bands are formed. This indicates that Lsi1 is required for the transport of Si through the cells of the exodermis and endodermis. Expression of Lsi1 displayed a distinct diurnal pattern. Furthermore, expression was transiently enhanced around the heading stage, which coincides with a high Si requirement during this growth stage. Expression was down-regulated by dehydration stress and abscisic acid, suggesting that expression of Lsi1 may be regulated by abscisic acid.

DOI： 10.1104/pp.106.093005

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