RESUMO

The Typha genus comprises plant species extensively studied for phytoremediation processes. Recently, Pseudomonas rhodesiae GRC140, an IAA-producing bacterium, was isolated from Typha latifolia roots. This bacterium stimulates the emergence of lateral roots of Arabidopsis thaliana in the presence and absence of cadmium. However, the bacterial influence on cadmium accumulation by the plant has not been determined. Moreover, the P. rhodesiae GRC140 effect in Cd phytoextraction by T. latifolia remains poorly understood. In this work, an axenic hydroponic culture of T. latifolia was established. The plants were used to evaluate the effects of cadmium stress in axenic plants and determine the effects of P. rhodesiae GRC140 and exogenous indole acetic acid (IAA) on Cd tolerance and Cd uptake by T. latifolia. Biomass production, total chlorophyll content, root electrolyte leakage, catalase activity, total glutathione, and Cd content were determined. The results showed that Cd reduces shoot biomass and increases total glutathione and Cd content in a dose-dependent manner in root tissues. Furthermore, P. rhodesiae GRC140 increased Cd translocation to the shoots, while IAA increased the Cd accumulation in plant roots, indicating that both treatments increase Cd removal by T. latifolia plants. These results indicate that axenic plants in hydroponic systems are adequate to evaluate the Cd effects in plants and suggest that T. latifolia phytoextraction abilities could be improved by P. rhodesiae GRC140 and exogenous IAA application.

RESUMO

BACKGROUND: A major limiting factor for plant growth is the aluminum (Al) toxicity in acidic soils, especially in tropical regions. The exclusion of Al from the root apex through root exudation of organic acids such as malate and citrate is one of the most ubiquitous tolerance mechanisms in the plant kingdom. Two families of anion channels that confer Al tolerance are well described in the literature, ALMT and MATE family. RESULTS: In this study, sugarcane plants constitutively overexpressing the Sorghum bicolor MATE gene (SbMATE) showed improved tolerance to Al when compared to non-transgenic (NT) plants, characterized by sustained root growth and exclusion of aluminum from the root apex based on the result obtained with hematoxylin staining. In addition, genome-wide analysis of the recently released sugarcane genome identified 11 ALMT genes and molecular studies showed potential new targets for aluminum tolerance. CONCLUSIONS: Our results indicate that the transgenic plants overexpressing the Sorghum bicolor MATE has an improved tolerance to Al. The expression profile of ALMT genes revels potential candidate genes to be used has an alternative for agricultural expansion in Brazil and other areas with aluminum toxicity in poor and acid soils.

Assuntos

RESUMO

Lead (Pb) contamination of agricultural soils, and subsequently of crops, has been widely reported. Soybean (Glycine max (L.) Merr.) has been indicated as a plant that accumulates Pb, even in soils that do not exceed the maximum permissible levels. Considering the toxicity of this heavy metal, the aim of the present study was to assess different concentrations of Pb, from low to extremely high (0.25 mM, 1 mM, and 2.5 mM), in soybean seedlings and their tolerance by analyzing morpho-physiological parameters in hydroponic experiments. Soybean seedlings were exposed to control and Pb treatments during 8 days, coinciding with the early growth stages, and the following variables were analyzed: biomass, Pb content in roots, stems and leaves, photosynthetic efficiency, leaf area, biochemical response (antioxidant power, chlorophylls, malondialdehyde), and relative water content of leaves. Results showed that roots accumulated much more Pb than the other organs, with Pb accumulation in roots being saturated even at the lowest Pb concentration, which was reflected in root biomass. Moreover, absorption of culture solutions was lower in Pb treatments, which was also reflected in the lower leaf relative water content. Lead toxicity symptoms in leaves (chlorosis and dark spots, and a decrease of biomass and leaf area, chlorophyll content, and photosynthetic efficiency), and an increase of the oxidative defense system were associated only with the highest Pb concentration (2.5 mM). Our findings support the evidence of soybean as a species tolerant to Pb, showing the effects of toxicity at very high concentrations.

Assuntos

RESUMO

Aluminium (Al) toxicity in acid soils is a major abiotic stress that can limit plant production worldwide. Al toxicity directly inhibits root development and exacerbates oxidative stress in the plant. Sugarcane is mostly cultivated in tropical regions and is often exposed to phytotoxic concentrations of soil Al. In this study, our objectives were to evaluate nine sugarcane cultivars on their tolerance to Al in a hydroponic system, investigating the effects of 143µM {Al3+} on root growth and on activity of the antioxidant enzymes ascorbate peroxidase (APX), catalase (CAT) and superoxide dismutase (SOD). The screening method proposed was suitable for a rapid, reliable and reproducible procedure of the sugarcane cultivars. Exposure to Al for three days altered root growth and activity of enzymes of the nine sugarcane cultivars. However, the magnitude of the alterations varied significantly among cultivars. The cultivar RB928064 was classified as Al-tolerant and the cultivar RB835486 as Al-sensitive. Increases in enzyme activity after Al exposure varied from 4 to 46%, with average increases of 19% in APX, 20% in CAT, and 8% in SOD. The variations induced by Al in enzyme activity, however, did not correlate significantly with those variations induced by Al in the root growth.

A toxidez por alumínio (Al) em solos ácidos é um dos principais estresses abióticos que podem limitara produção vegetal pelo mundo todo. A toxidez por Al inibe diretamente o desenvolvimento radicular e aumenta a produção de espécies reativas de oxigênio na planta. A cana-de-açúcar é mais cultivada em regiões tropicais e frequentemente está exposta a concentrações fitotóxicas de Al no solo. Neste estudo, nossos objetivos foram avaliar a tolerância ao Al de nove cultivares de cana-de-açúcar em um sistema hidropônico e investigar os efeitos de 143µM {Al3+} sobre o crescimento radicular e a atividade das enzimas antioxidantes ascorbato peroxidase (APX), catalase (CAT) e superóxido dismutase (SOD). O método de triagem proposto foi adequado para a avaliação de tolerância ao Al de forma rápida, confiável e reprodutível. A exposição ao Al por três dias alterou o crescimento radicular e a atividade das enzimas nas nove cultivares de cana-de-açúcar. Entretanto, a magnitude das alterações variou significativamente entre as cultivares. A cultivar RB928064 foi classificada como tolerante e a cultivar RB835486 como sensível ao Al. Os incrementos de atividade enzimática após exposição ao Al variaram entre 4 e 46%,com incrementos médios de 19% para APX, 20% para CAT, e 8% para SOD. As variações induzidas pelo Al sobre a atividade enzimática, entretanto, não apresentaram correlações significativas com aquelas induzidas pelo Al sobre o crescimento radicular.

Assuntos

RESUMO

Aluminium (Al) toxicity in acid soils is a major abiotic stress that can limit plant production worldwide. Al toxicity directly inhibits root development and exacerbates oxidative stress in the plant. Sugarcane is mostly cultivated in tropical regions and is often exposed to phytotoxic concentrations of soil Al. In this study, our objectives were to evaluate nine sugarcane cultivars on their tolerance to Al in a hydroponic system, investigating the effects of 143µM {Al3+} on root growth and on activity of the antioxidant enzymes ascorbate peroxidase (APX), catalase (CAT) and superoxide dismutase (SOD). The screening method proposed was suitable for a rapid, reliable and reproducible procedure of the sugarcane cultivars. Exposure to Al for three days altered root growth and activity of enzymes of the nine sugarcane cultivars. However, the magnitude of the alterations varied significantly among cultivars. The cultivar RB928064 was classified as Al-tolerant and the cultivar RB835486 as Al-sensitive. Increases in enzyme activity after Al exposure varied from 4 to 46%, with average increases of 19% in APX, 20% in CAT, and 8% in SOD. The variations induced by Al in enzyme activity, however, did not correlate significantly with those variations induced by Al in the root growth.(AU)

A toxidez por alumínio (Al) em solos ácidos é um dos principais estresses abióticos que podem limitara produção vegetal pelo mundo todo. A toxidez por Al inibe diretamente o desenvolvimento radicular e aumenta a produção de espécies reativas de oxigênio na planta. A cana-de-açúcar é mais cultivada em regiões tropicais e frequentemente está exposta a concentrações fitotóxicas de Al no solo. Neste estudo, nossos objetivos foram avaliar a tolerância ao Al de nove cultivares de cana-de-açúcar em um sistema hidropônico e investigar os efeitos de 143µM {Al3+} sobre o crescimento radicular e a atividade das enzimas antioxidantes ascorbato peroxidase (APX), catalase (CAT) e superóxido dismutase (SOD). O método de triagem proposto foi adequado para a avaliação de tolerância ao Al de forma rápida, confiável e reprodutível. A exposição ao Al por três dias alterou o crescimento radicular e a atividade das enzimas nas nove cultivares de cana-de-açúcar. Entretanto, a magnitude das alterações variou significativamente entre as cultivares. A cultivar RB928064 foi classificada como tolerante e a cultivar RB835486 como sensível ao Al. Os incrementos de atividade enzimática após exposição ao Al variaram entre 4 e 46%,com incrementos médios de 19% para APX, 20% para CAT, e 8% para SOD. As variações induzidas pelo Al sobre a atividade enzimática, entretanto, não apresentaram correlações significativas com aquelas induzidas pelo Al sobre o crescimento radicular.(AU)

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RESUMO

Acidic soils are distributed worldwide, predominantly in tropical and subtropical areas, reaching around 50% of the arable soil. This type of soil strongly reduces crop production, mainly because of the presence of aluminum, which has its solubility increased at low pH levels. A well-known physiological mechanism used by plants to cope with Al stress involves activation of membrane transporters responsible for organic acid anions secretion from the root apex to the rhizosphere, which chelate Al, preventing its absorption by roots. In sorghum, a membrane transporter gene belonging to multidrug and toxic compound extrusion (MATE) family was identified and characterized as an aluminum-activated citrate transporter gene responsible for Al tolerance in this crop. Setaria viridis is an emerging model for C4 species and it is an important model to validate some genes for further C4 crops transformation, such as sugarcane, maize, and wheat. In the present work, Setaria viridis was used as a model plant to overexpress a newly identified MATE gene from Brachypodium distachyon (BdMATE), closely related to SbMATE, for aluminum tolerance assays. Transgenic S. viridis plants overexpressing a BdMATE presented an improved Al tolerance phenotype, characterized by sustained root growth and exclusion of aluminum from the root apex in transgenic plants, as confirmed by hematoxylin assay. In addition, transgenic plants showed higher root citrate exudation into the rhizosphere, suggesting that Al tolerance improvement in these plants could be related to the chelation of the metal by the organic acid anion. These results suggest that BdMATE gene can be used to transform C4 crops of economic importance with improved aluminum tolerance.

RESUMO

Empiricism in the use of nutrient solutions is frequent. Several times the same nutrient solution is used to grow different species based only on morphological similarities. This practice may lead to nutritional imbalances, affecting not only the production but also the quality of the product due to an accumulation of nitrate. An experiment under hydroponic conditions - the NFT system - was conducted with the aim of evaluating the effect of the concentration of nitrogen in the nutrient solution on the production and on the nutrient and nitrate contents of rocket (Eruca sativa) salad leaves. The experiment was carried out in spring 2003, in a randomized block design and in a 4 x 3 factorial design, with four replicates. Four nitrogen concentrations in the nutrient solution (60.8; 121.6; 182.5; 243.5 mg L-1) and three rocket salad cultivars (Cultivada, Folha Larga and Selvática) were evaluated. Cv. Cultivada produced the tallest plants and the highest leaf fresh fitomass, not differing from cv. 'Folha Larga' in the number of leaves, leaf nitrate content, root dry fitomass and root fresh fitomass. An increment in NO3, N, Ca and P and a reduction in Mg, K and S occurred when the concentration of N in the nutrient solution was increased. Cultivation of cv. Cultivada at the concentration of 93 mg L-1 is the most recommended as it provides the highest yield and low nitrate content.

O empirismo no uso das soluções nutritivas é freqüente. Muitas vezes a mesma solução nutritiva é usada para diferentes espécies baseando-se apenas em semelhanças morfológicas. No entanto esta situação pode proporcionar desequilíbrio nutricional prejudicando tanto a produção quanto a qualidade do produto face o acúmulo de nitrato. Foi conduzido um trabalho em sistema hidropônico - NFT, com o objetivo de avaliar o efeito da concentração de nitrogênio na solução nutritiva na produção, nos teores de nutrientes e de nitrato em folhas de rúcula (Eruca sativa). O trabalho foi conduzido na primavera de 2003. Foram avaliadas quatro concentrações de nitrogênio na solução nutritiva (60,8; 121,6; 182,5; 243,5 mg L-1) e três cultivares de rúcula (Cultivada, Folha Larga e Selvática), sob delineamento de blocos ao acaso, fatorial 4 x 3, com quatro repetições. A cv. Cultivada apresentou maior estatura e fitomassa fresca de folhas, não diferindo da 'Folha Larga' quanto a número de folhas, teor de nitrato nas folhas e fitomassa seca e fresca da raiz. Houve incremento de NO3-, N, Ca e P e diminuição de Mg, K e S com o aumento da concentração de N na solução nutritiva. O cultivo da cv. Cultivada na concentração de 93 mg L-1 é a mais recomendada em função da maior produtividade e baixo teor de nitrato.

RESUMO

Empiricism in the use of nutrient solutions is frequent. Several times the same nutrient solution is used to grow different species based only on morphological similarities. This practice may lead to nutritional imbalances, affecting not only the production but also the quality of the product due to an accumulation of nitrate. An experiment under hydroponic conditions - the NFT system - was conducted with the aim of evaluating the effect of the concentration of nitrogen in the nutrient solution on the production and on the nutrient and nitrate contents of rocket (Eruca sativa) salad leaves. The experiment was carried out in spring 2003, in a randomized block design and in a 4 x 3 factorial design, with four replicates. Four nitrogen concentrations in the nutrient solution (60.8; 121.6; 182.5; 243.5 mg L-1) and three rocket salad cultivars (Cultivada, Folha Larga and Selvática) were evaluated. Cv. Cultivada produced the tallest plants and the highest leaf fresh fitomass, not differing from cv. 'Folha Larga' in the number of leaves, leaf nitrate content, root dry fitomass and root fresh fitomass. An increment in NO3, N, Ca and P and a reduction in Mg, K and S occurred when the concentration of N in the nutrient solution was increased. Cultivation of cv. Cultivada at the concentration of 93 mg L-1 is the most recommended as it provides the highest yield and low nitrate content.

O empirismo no uso das soluções nutritivas é freqüente. Muitas vezes a mesma solução nutritiva é usada para diferentes espécies baseando-se apenas em semelhanças morfológicas. No entanto esta situação pode proporcionar desequilíbrio nutricional prejudicando tanto a produção quanto a qualidade do produto face o acúmulo de nitrato. Foi conduzido um trabalho em sistema hidropônico - NFT, com o objetivo de avaliar o efeito da concentração de nitrogênio na solução nutritiva na produção, nos teores de nutrientes e de nitrato em folhas de rúcula (Eruca sativa). O trabalho foi conduzido na primavera de 2003. Foram avaliadas quatro concentrações de nitrogênio na solução nutritiva (60,8; 121,6; 182,5; 243,5 mg L-1) e três cultivares de rúcula (Cultivada, Folha Larga e Selvática), sob delineamento de blocos ao acaso, fatorial 4 x 3, com quatro repetições. A cv. Cultivada apresentou maior estatura e fitomassa fresca de folhas, não diferindo da 'Folha Larga' quanto a número de folhas, teor de nitrato nas folhas e fitomassa seca e fresca da raiz. Houve incremento de NO3-, N, Ca e P e diminuição de Mg, K e S com o aumento da concentração de N na solução nutritiva. O cultivo da cv. Cultivada na concentração de 93 mg L-1 é a mais recomendada em função da maior produtividade e baixo teor de nitrato.