RESUMEN
The relationships between the concentration of metal in the growth medium, Cs, the concentration of metal absorbed by the plant, Cp, and the total biomass achieved, M, all of which are factors relevant to the efficiency of metal uptake and tolerance by the plant, have been investigated via the physiological response of Brassica juncea seedlings to Ni stress. The factorial growth experiments treated the Ni concentration in agar medium and the diurnal light quanta as independently variable parameters. Observations included the evidence of light enhancement of Ni toxicity in the root, as well as at the whole-plant level. The shoot mass index possibly is an indicator of the amount of shoot metal sequestration in B. juncea, as are the logarithmic variation of Cp with Cs and the power-law dependence of M on Cp. The sum total of these observations indicates that, for the Ni accumulating plant B. juncea, the overall metabolic allocation to either growth or metal tolerance of the plant is important. Neither a rapid biomass increase nor a high metal absorbed concentration favored the removal of high metal mass from the medium. Rather, the plants with a moderate rate of biomass growth and a moderate absorbed metal concentration demonstrated the ability to remove the maximum mass of metal from the medium. The implication of these results as related to the extant model of phyoextraction efficiency is discussed.
Asunto(s)
Brassica/metabolismo , Luz , Níquel/metabolismo , Plantones/metabolismo , Biomasa , Brassica/crecimiento & desarrollo , Brassica/efectos de la radiación , Oscuridad , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/metabolismo , Brotes de la Planta/crecimiento & desarrollo , Brotes de la Planta/metabolismo , Teoría Cuántica , Plantones/efectos de la radiación , Espectrofotometría Atómica/métodosRESUMEN
The ability of Thlaspi goesingense to hyperaccumulate Ni seems to be governed in part by enhanced accumulation of Ni within leaf vacuoles. We have characterized genes from T. goesingense encoding putative vacuolar metal ion transport proteins, termed metal tolerance proteins (TgMTPs). These proteins contain all of the features of cation-efflux family members, and evidence indicates they are derived from a single genomic sequence (TgMTP1) that gives rise to an unspliced (TgMTP1t1) and a spliced (TgMTP1t2) transcript. Heterologous expression of these transcripts in yeast lacking the TgMTP1 orthologues COT1 and ZRC1 complements the metal sensitivity of these yeast strains, suggesting that TgMTP1s are able to transport metal ions into the yeast vacuole in a manner similar to COT1 and ZRC1. The unspliced and spliced TgMTP1 variants differ within a histidine-rich putative metal-binding domain, and these sequence differences are reflected as alterations in the metal specificities of these metal ion transporters. When expressed in yeast, TgMTP1t1 confers the highest level of tolerance to Cd, Co, and Zn, whereas TgMTP1t2 confers the highest tolerance to Ni. TgMTP1 transcripts are highly expressed in T. goesingense compared with orthologues in the nonaccumulators Arabidopsis thaliana, Thlaspi arvense, and Brassica juncea. We propose that the high-level expression of TgMTP1 in T. goesingense accounts for the enhanced ability of this hyperaccumulator to accumulate metal ions within shoot vacuoles.
Asunto(s)
Proteínas Portadoras/metabolismo , Proteínas de Transporte de Catión , Níquel/metabolismo , Proteínas de Plantas/metabolismo , Plantas/metabolismo , Proteínas de Saccharomyces cerevisiae , Secuencia de Aminoácidos , Arabidopsis/metabolismo , Brassica/metabolismo , Cadmio/metabolismo , Cadmio/toxicidad , Proteínas Portadoras/genética , Cationes/metabolismo , Cobalto/metabolismo , Cobalto/toxicidad , Resistencia a Medicamentos/genética , Farmacorresistencia Microbiana/genética , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Transporte Iónico , Proteínas de Transporte de Membrana , Datos de Secuencia Molecular , Níquel/toxicidad , Proteínas de Plantas/genética , Brotes de la Planta/metabolismo , Brotes de la Planta/ultraestructura , Plantas/genética , Reacción en Cadena de la Polimerasa , Isoformas de Proteínas/metabolismo , Estructura Terciaria de Proteína , Empalme del ARN , Proteínas Recombinantes de Fusión/metabolismo , Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/ultraestructura , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Especificidad por Sustrato , Vacuolas/metabolismo , Zinc/metabolismo , Zinc/toxicidadRESUMEN
Uptake and translocation of cationic nutrients play essential roles in physiological processes including plant growth, nutrition, signal transduction, and development. Approximately 5% of the Arabidopsis genome appears to encode membrane transport proteins. These proteins are classified in 46 unique families containing approximately 880 members. In addition, several hundred putative transporters have not yet been assigned to families. In this paper, we have analyzed the phylogenetic relationships of over 150 cation transport proteins. This analysis has focused on cation transporter gene families for which initial characterizations have been achieved for individual members, including potassium transporters and channels, sodium transporters, calcium antiporters, cyclic nucleotide-gated channels, cation diffusion facilitator proteins, natural resistance-associated macrophage proteins (NRAMP), and Zn-regulated transporter Fe-regulated transporter-like proteins. Phylogenetic trees of each family define the evolutionary relationships of the members to each other. These families contain numerous members, indicating diverse functions in vivo. Closely related isoforms and separate subfamilies exist within many of these gene families, indicating possible redundancies and specialized functions. To facilitate their further study, the PlantsT database (http://plantst.sdsc.edu) has been created that includes alignments of the analyzed cation transporters and their chromosomal locations.
Asunto(s)
Arabidopsis/genética , Proteínas Portadoras/genética , Proteínas de Transporte de Catión , Canales Iónicos/genética , Antiportadores/clasificación , Antiportadores/genética , Arabidopsis/clasificación , Transporte Biológico Activo , Proteínas Portadoras/clasificación , Proteínas Portadoras/metabolismo , Cationes , Mapeo Cromosómico , Canales Catiónicos Regulados por Nucleótidos Cíclicos , Canales Iónicos/clasificación , Transporte Iónico/genética , Proteínas de la Membrana/metabolismo , Filogenia , Potasio/metabolismoRESUMEN
Plants use a diverse array of cytochrome P450 monooxygenases in their biosynthetic and detoxification pathways. To determine the extent to which various maize P450s are induced in response to chemical inducers, such as naphthalic anhydride (NA), triasulfuron (T), phenobarbital, and bacterial pathogens (Erwinia stuartii, Acidovorax avenae), we have analyzed the response patterns of seven P450 transcripts after treatment of seedlings with these inducers. Each of these P450 transcripts has distinct developmental, tissue-specific, and chemical cues regulating their expression even when they encode P450s within the same biosynthetic pathway. Most notably, the CYP71C1 and CYP71C3 transcripts, encoding P450s in the DIMBOA biosynthetic pathway, are induced to the same level in response to wounding and NA treatment of younger seedlings and differentially in response to NA/T treatment of younger seedlings and NA and NA/T treatment of older seedlings. NA and T induce expression of both CYP92A1 and CYP72A5 transcripts in older seedling shoots, whereas phenobarbital induces CYP92A1 expression in older seedling shoots and highly induces CYP72A5 expression in young and older seedling roots. Expressed sequence tag (EST) 6c06b11 transcripts, encoding an undefined P450 activity, are highly induced in seedling shoots infected with bacterial pathogens.
Asunto(s)
Sistema Enzimático del Citocromo P-450/metabolismo , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Herbicidas/farmacología , Oxigenasas de Función Mixta/metabolismo , Zea mays/enzimología , Secuencia de Aminoácidos , Sistema Enzimático del Citocromo P-450/química , Sistema Enzimático del Citocromo P-450/genética , Inducción Enzimática , Regulación Enzimológica de la Expresión Génica/efectos de los fármacos , Oxigenasas de Función Mixta/química , Oxigenasas de Función Mixta/genética , Datos de Secuencia Molecular , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Zea mays/efectos de los fármacos , Zea mays/genéticaAsunto(s)
Níquel/farmacocinética , Plantas/metabolismo , Selenio/farmacocinética , Zinc/farmacocinética , Disponibilidad Biológica , Evolución Biológica , Transporte Biológico Activo , Biotecnología , Membrana Celular/metabolismo , Genes de Plantas , Ingeniería Genética , Brotes de la Planta/metabolismo , Plantas/genética , Plantas Comestibles/genética , Plantas Comestibles/metabolismo , Plantas Modificadas GenéticamenteRESUMEN
To understand the role of free histidine (His) in Ni hyperaccumulation in Thlaspi goesingense, we investigated the regulation of His biosynthesis at both the molecular and biochemical levels. Three T. goesingense cDNAs encoding the following His biosynthetic enzymes, ATP phosphoribosyltransferase (THG1, GenBank accession no. AF003347), imidazoleglycerol phosphate dehydratase (THB1, GenBank accession no. AF023140), and histidinol dehydrogenase (THD1, GenBank accession no. AF023141) were isolated by functional complementation of Escherichia coli His auxotrophs. Northern analysis of THG1, THD1, and THB1 gene expression revealed that each gene is expressed in both roots and shoots, but at the concentrations and dosage times of Ni treatment used in this study, these genes failed to show any regulation by Ni. We were also unable to observe any increases in the concentration of free His in root, shoot, or xylem sap of T. goesingense in response to Ni exposure. X-ray absorption spectroscopy of root and shoot tissue from T. goesingense and the non-accumulator species Thlaspi arvense revealed no major differences in the coordination of Ni by His in these tissues. We therefore conclude that the Ni hyperaccumulation phenotype in T. goesingense is not determined by the overproduction of His in response to Ni.
Asunto(s)
ATP Fosforribosil Transferasa/genética , Oxidorreductasas de Alcohol/genética , Histidina/metabolismo , Hidroliasas/genética , Níquel/metabolismo , Filogenia , Plantas/enzimología , Plantas/genética , ATP Fosforribosil Transferasa/química , Oxidorreductasas de Alcohol/química , Secuencia de Aminoácidos , Clonación Molecular , Escherichia coli , Evolución Molecular , Biblioteca de Genes , Hidroliasas/química , Datos de Secuencia Molecular , Alineación de Secuencia , Homología de Secuencia de AminoácidoRESUMEN
Cytochrome P450 monooxygenases play paramount roles in the detoxification of herbicides as well as in the synthesis of lignins, flavonoids, and phenolic acids. Biochemical analysis of triasulfuron metabolism in maize (Zea mays) seedlings has demonstrated that the P450(s) responsible for detoxification of this herbicide is induced by naphthalic anhydride (NA), a plant safener, and by triasulfuron, the herbicide itself. Induction studies conducted with seedlings of different ages suggest that two separate response pathways modulate this P-450 activity. Induction by NA is independent of the developmental age of the seedlings up to 6.5 d; induction by triasulfuron is tightly modulated with respect to developmental age in that triasulfuron metabolism can be induced by triasulfuron in young (2.5 d) but not older (6.5 d) seedlings. Induction by NA administered in combination with triasulfuron synergistically enhances triasulfuron metabolism in younger seedlings to levels substantially above that obtained with either herbicide or safener treatment alone. In older seedlings, NA plus triasulfuron treatment induces triasulfuron metabolism to only the level of NA treatment alone, indicating again that the induction cascade responding to triasulfuron is nonfunctional in later development. MnCl2 studies indicate that the triasulfuron insensitivity of older seedlings does not result from a general limitation in the inducibility of this P-450 detoxification system but rather from specific limitations in the triasulfuron-response pathway.