Crescimento e expressão gênica em clones de eucalipto influenciados pelo boro e déficit hídrico

• Autor(a) principal: Nunes, Flancer Novais
• Data de Publicação: 2010
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1603
• topic: Estresse hídrico; Seca de ponteiro; Eucalyptus; Water stress; Dry pointer; Eucalyptus; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO

The increasing of the eucalypt plantation in the Cerrado region in Brazil has increasing the need to develop eucalypt clones tolerant to water stress, the main limiting factor to tree productivity in this region. Water deficit also induce B deficiency in eucalypt trees growing in these region, leading to frequent B fertilizations. During the dry season, B deficiency symptoms are more common, because the low soil water content leads to a reduced B transport rate through the soil, and, also, to a lower B uptake. Boron has been related to physiological mechanisms which provide higher plant drought tolerance, as, for example: higher root:shoot relation; thus, water and B have a synergistc effect. The objectives of this study was: 1) to evaluate the relationship between carbon isotope discrimination (δ13C) and drought tolerance in eucalypt clones; 2) to verify the influence of B availability for eucalypt clones, cultivated under restricted water availability, on water stress and gene transcription pattern. For the first objective eucalypt stands of Eucalyptus urophylla clones, one sensible (3334) and the other tolerant (3335) to water stress, with four years of age, growing in Brasília de Minas e Bocaiúva counties - Minas Gerais State -, were selected at the end of the dry season of 2007. We evaluated leaf water potential (Ψwl), δ13C, plant survival index and stem productivity. For the second objective, seedlings of the 3334 and 3335 clones, were submitted to the absence or presence of 15 μmol L-1 of B and to the water potentials of -0,05 and -1,5 MPa. Ten days after treatment application, 1 g of leaf and root samples were collected for RNA extraction, and, then, the plants were separated in leaf, stem and root to determine the dry matter production. At the harvesting time, leaf water potential, photosynthesis, stomata conductance and transpiration rate were determined. Four genes related to B and polyol transport and four genes related to cell wall synthesis were selected, and analyzed by RT-PCR. The tolerant clone presented smaller δ13C and Ψwl than the sensible one, and higher survival index. There was no difference in the δ13C values between trees of the same clone cultivated in the two counties. The results suggest that δ13C can be used as an indicator of drought tolerance for eucalypt clones when cultivated under water restriction. The water availability was the main factor affecting biomass production in both clones. Boron application improved shoot biomass production, photosynthesis, stomata conductance andtranspiration rate. Shoot dry mass production by the tolerant clone was higher, when B was added, as compared to absence of B, suggesting that this micronutrient improved drought tolerance. The genes related to B and polyol transport, and those related to cell wall synthesis, presented higher relative expression in roots tissue of the tolerant clone, cultivated under water stress, on B presence. It is suggested that both gene classes are involved in cell wall synthesis: first, higher polyol transporter gene expression provide carbon source; second, B transporters will provide adequate B supply to polymerization of pectin compounds; and thirty, the direct effect of higher gene expression of the genes related to cell wall syntheses We pointed that all of the genes presented higher relative expression in the root, signaling for higher root system development, a strategy that contributes to a higher water and nutrient acquisition, overcoming problems related to a long drought period.