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| Author(s): |
Alejandra Matiz Lopez
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB) |
| Defense date: | 2017-06-29 |
| Examining board members: |
Helenice Mercier;
Halley Caixeta de Oliveira;
Maria Magdalena Rossi;
Sarah Caroline Ribeiro de Souza;
Fernanda Staniscuaski
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| Advisor: | Helenice Mercier; Marília Gaspar |
| Abstract | |
Organic molecules can be the main input of nitrogen for plants in environments where inorganic nitrogen sources are limited, such as the epiphytic habitat. Recent studies have shown a high capacity of Vriesea gigantean, an epiphytic tank-forming bromeliad, to absorb urea by their leaves, making this bromeliad an excellent model to study urea metabolism. Nevertheless, urea uptake and assimilation processes are little characterized in these plants. Several plant aquaporins from different species are able to facilitate the diffusion of urea through the membranes. Three foliar aquaporin genes, VgPIP1;2, VgPIP1;5 and VgTIP2, have been recently cloned from urea-treated V. gigantea plants. The expression of VgPIP1;5 and VgTIP2 was specifically up-regulated by urea in the basal part of the leaves. Nevertheless, it had not been tested whether these aquaporins were in fact capable of facilitating the membrane diffusion of either urea, ammonium or water. Moreover, it was suggested that after urea absorption, this organic N compound is hydrolyzed by the urease enzyme into CO2 and NH4+ prior to NH4+ assimilation by the GS/GOGAT pathway. In the present project, urea, NH4+/NH3 and water diffusion through VgPIP1;2, VgPIP1;5 and VgTIP2 were determined by uptake studies in Xenopus laevis oocytes (urea and water)and complementation assay in Saccharomyces cerevisiae (NH4+/NH3). The results showed that while VgTIP2 facilitates water transport when expressed alone in oocytes, VgPIP1;2 and VgPIP1;5 needed to be co-expressed with a PIP2 aquaporin to be targeted to the plasma membrane and act as water channels. Moreover, VgTIP2 was the only aquaporin able to facilitate the diffusion of urea through the membrane, while VgPIP1;2 seems to be capable of transporting NH4+/NH3. Additionally, the urease relevance in the urea assimilation process was investigated through the analysis of the amino acid profile in V. gigantea plants kept under a urease inhibitor (chloranil) and supplied with labeled [13C]-[ 15N]2-urea. The experiments were conducted in atmosphheric and adult-tank ontogenetic stages of V. gigantea due to their metabolic and morphological differences. The results suggested that urease activity may be a limiting step in the conversion of N from urea to ammonium. Moreover, decreases in urease activity by chloranil impared the first steps in N assimilation, droping the pool of glutamine (Gln) in atmospheric plants. In adult-tank plants the transamination appeared to be adversely affected. Those differences in urea assimilation might be due to differences in the morphology and the nutrient capture strategies of the ontogenetic phases. Finally, direct urea assimilation process (without previous urea hydrolysis) in V. gigantea plants seems unlikely to occur (AU) | |
| FAPESP's process: | 13/09097-7 - Characterization of the absorption of urea via aquaporins and its possible direct assimilation by Vriesea gigantea (Bromeliaceae) |
| Grantee: | Alejandra Matiz Lopez |
| Support Opportunities: | Scholarships in Brazil - Doctorate |