Efeito da redução do transporte da sacarose nas células-guarda na resposta ao estresse osmótico e expressão protéica

• Autor(a) principal: Pinheiro, Daniela Pereira
• Data de Publicação: 2011
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4324
• topic: Células-guarda; Transportador de sacarose; Proteoma; Estômato; Guard-cells; Sucrose transporter; Proteome; Stomata; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::FISIOLOGIA VEGETAL

Studies indicate that sucrose has an important role in guard cell osmoregulation (GC) and the current hypotheis is that this sucrose in transported from mesophyl cells. Plants of Nicotiana tabacum transformed with an antisense gene construct for sucrose transporter (P62) driven by KST1, a GC specific promoter, exhibit lower stomatal conductance and higher water use efficiency compared to wild type plants (WT), resulting in plants with lower water consumption. Osmotic stress produced by cultivation under hidroponic solution in the presence of PEG resulted in a reduction in total leaf area in all plants, being this reduction lower in P62 plants. A reduction in photosynthesis (A) under these conditions of osmotic stress, which was observed only in non-transformed plants, was associated with lower stomatal conductance (gs) and a reduction in Ci/Ca. The photosynthetic rate during treatment with 2.0% PEG and under high CO2 concentrations was reduced by 31%, indicating that there is a biochemical limitation of photosynthesis produced by this level of osmotic stress. However, this observation cannot be explained by increased oxidative damage, as there was no change in the level of lipid peroxidation. Additionally there were no differences in Fv/Fm, Y(II), ETR and qP, for the plants assessed, showing that both wild type and transgenic plants did not exhibit limitations in their use of excitation energy for photochemical reactions. However, WT plants subjected to osmotic stress (1.5% and 2.0% PEG) showed higher values of qN, indicating a higher thermal dissipation. Comparison of the guard cell proteome, P62 guard cells showed increased expression of key proteins related to photosynthetic carbon fixation such as sedoheptulose-1,7-bisphosphatase and Rubisco activase, suggesting a greater rate of CO2 assimilation and Calvin cycle activity, what could suggest a homestatic mecanism to maintain the sucrose level in these cells. Presence of photosynthesis in guard cells could be also supported by the identification of PsaD subunit of photosystem I and some subunits of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco). Data from the differential proteomic analysis of leaves revealed no significant differences between WT and P62 plants, consistent with the use of a guard cell specific promoter to drive expression of the antisense construct. As conclusion, this work suggests that reductions in sucrose transport could contribute for higher tolerance to osmotic stress and water use effciency.