RESUMO

Urease catalyzes the hydrolysis of urea to ammonia and carbon dioxide. The ammonia (nitrogen (N) product of urease activity) is incorporated into organic compounds. Thus, urease is involved in N remobilization, as well as in primary N assimilation. Two urease isoforms have been described for soybean: the embryo-specific, encoded by the Eu1 gene, and the ubiquitous urease, encoded by Eu4. A third urease-encoding gene was recently identified, designated Eu5, which encodes the putative protein product SBU-III. The present study aimed to evaluate the contribution of soybean ureases to seed germination and plant development. Analyses were performed using Eu1/Eu4/Eu5-co-suppressed transgenic plants and mutants of the Eu1 and Eu4 urease structural genes, as well as a urease-null mutant (eu3-a) that activates neither the ubiquitous nor embryo-specific ureases. The co-suppressed plants presented a developmental delay during the first month after germination; shoots and roots were significantly smaller and lighter. Slower development was observed for the double eu1-a/eu4-a mutant and the eu3-a single mutant. The N content in transgenic plants was significantly lower than in non-transgenic plants. Among the mutants, eu3-a presented the lowest and eu1-a the highest N content. Altogether, these results indicate that increased ureolytic activity plays an important role in plant development.

RESUMO

Abstract Urease catalyzes the hydrolysis of urea to ammonia and carbon dioxide. The ammonia (nitrogen (N) product of urease activity) is incorporated into organic compounds. Thus, urease is involved in N remobilization, as well as in primary N assimilation. Two urease isoforms have been described for soybean: the embryo-specific, encoded by the Eu1 gene, and the ubiquitous urease, encoded by Eu4. A third urease-encoding gene was recently identified, designated Eu5, which encodes the putative protein product SBU-III. The present study aimed to evaluate the contribution of soybean ureases to seed germination and plant development. Analyses were performed using Eu1/Eu4/Eu5-co-suppressed transgenic plants and mutants of the Eu1 and Eu4 urease structural genes, as well as a urease-null mutant (eu3-a) that activates neither the ubiquitous nor embryo-specific ureases. The co-suppressed plants presented a developmental delay during the first month after germination; shoots and roots were significantly smaller and lighter. Slower development was observed for the double eu1-a/eu4-a mutant and the eu3-a single mutant. The N content in transgenic plants was significantly lower than in non-transgenic plants. Among the mutants, eu3-a presented the lowest and eu1-a the highest N content. Altogether, these results indicate that increased ureolytic activity plays an important role in plant development.

RESUMO

The element Ni is considered an essential plant micronutrient because it acts as an activator of the enzyme urease. Recent studies have shown that Ni may activate an isoform of glyoxalase I, which performs an important step in the degradation of methylglyoxal (MG), a potent cytotoxic compound naturally produced by cellular metabolism. Reduced glutathione (GSH) is consumed and regenerated in the process of detoxification of MG, which is produced during stress (stress-induced production). We examine the role of Ni in the relationship between the MG cycle and GSH homeostasis and suggest that Ni may have a key participation in plant antioxidant metabolism, especially in stressful situations.

RESUMO

Ureases are abundant in plants, bacteria, and in the soil, but their role in signaling between soybean and soil microorganisms has not been investigated. The bacterium Bradyrhizobium japonicum forms nitrogen-fixing nodules on soybean roots. Here, we evaluated the role(s) of ureases in the process of soybean nodulation. Chemotaxis assays demonstrated that soybean and jack bean ureases were more chemotactic toward bacterial cells than the corresponding plant lectins. The eu1-a,eu4 soybean, deficient in urease isoforms, formed fewer but larger nodules than the wild-type, regardless of the bacterial urease phenotype. Leghemoglobin production in wild-type plants was higher and peaked earlier than in urease-deficient plants. Inhibition of urease activity in wild-type plants did not result in the alterations seen in mutated plants. We conclude that soybean urease(s) play(s) a role in the soybean-B. japonicum symbiosis, which is independent of its ureolytic activity. Bacterial urease does not play a role in nodulation.

Assuntos

Bradyrhizobium/fisiologia , Glycine max/enzimologia , Proteínas de Plantas/metabolismo , Nodulação , Nódulos Radiculares de Plantas/enzimologia , Urease/metabolismo , Nódulos Radiculares de Plantas/microbiologia , Glycine max/microbiologia , Glycine max/fisiologia , Simbiose

RESUMO

The soybean ubiquitous urease (encoded by GmEu4) is responsible for recycling metabolically derived urea. Additional biological roles have been demonstrated for plant ureases, notably in toxicity to other organisms. However, urease enzymatic activity is not related to its toxicity. The role of GmEu4 in soybean susceptibility to fungi was investigated in this study. A differential expression pattern of GmEu4 was observed in susceptible and resistant genotypes of soybeans over the course of a Phakopsora pachyrhizi infection, especially 24 h after infection. Twenty-nine adult, transgenic soybean plants, representing six independently transformed lines, were obtained. Although the initial aim of this study was to overexpress GmEu4, the transgenic plants exhibited GmEu4 co-suppression and decreased ureolytic activity. The growth of Rhizoctonia solani, Phomopsis sp., and Penicillium herguei in media containing a crude protein extract from either transgenic or non-transgenic leaves was evaluated. The fungal growth was higher in the protein extracts from transgenic urease-deprived plants than in extracts from non-transgenic controls. When infected by P. pachyrhizi uredospores, detached leaves of urease-deprived plants developed a significantly higher number of lesions, pustules and erupted pustules than leaves of non-transgenic plants containing normal levels of the enzyme. The results of the present work show that the soybean plants were more susceptible to fungi in the absence of urease. It was not possible to overexpress active GmEu4. For future work, overexpression of urease fungitoxic peptides could be attempted as an alternative approach.

Assuntos

Basidiomycota/crescimento & desenvolvimento , Glycine max/enzimologia , Doenças das Plantas/microbiologia , Urease/metabolismo , Bioensaio , DNA Bacteriano/genética , Resistência à Doença/genética , Regulação da Expressão Gênica de Plantas , Vetores Genéticos/genética , Doenças das Plantas/genética , Folhas de Planta/microbiologia , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas Geneticamente Modificadas , Recombinação Genética/genética , Glycine max/genética , Glycine max/microbiologia , Transformação Genética , Transgenes/genética , Ureia/metabolismo

RESUMO

THE ROOT EPIDERMIS IS COMPOSED OF TWO CELL TYPES: trichoblasts (or hair cells) and atrichoblasts (or non-hair cells). In lettuce (Lactuca sativa cv. Grand Rapids var. Rapidmor oscura) plants grown hydroponically in water, the root epidermis did not form root hairs. The addition of 10 microM sodium nitroprusside (SNP), a nitric oxide (NO) donor, resulted in almost all rhizodermal cells differentiated into root hairs. Treatment with the synthetic auxin 1-naphthyl acetic acid (NAA) displayed a significant increase of root hair formation (RHF) that was prevented by the specific NO scavenger carboxy-PTIO (cPTIO). In Arabidopsis, two mutants have been shown to be defective in NO production and to display altered phenotypes in which NO is implicated. Arabidopsis nos1 has a mutation in an NO synthase structural gene (NOS1), and the nia1 nia2 double mutant is null for nitrate reductase (NR) activity. We observed that both mutants were affected in their capacity of developing root hairs. Root hair elongation was significantly reduced in nos1 and nia1 nia2 mutants as well as in cPTIO-treated wild type plants. A correlation was found between endogenous NO level in roots detected by the fluorescent probe DAF-FM DA and RHF. In Arabidopsis, as well as in lettuce, cPTIO blocked the NAA-induced root hair elongation. Taken together, these results indicate that: (1) NO is a critical molecule in the process leading to RHF and (2) NO is involved in the auxin-signaling cascade leading to RHF.