Respostas fisiológicas à hipóxia e a manganês em clones de eucalipto com tolerância diferencial à Seca de Ponteiros do Vale do Rio Doce

• Ano de defesa: 2013
• Autor(a) principal: Harguindeguy, Ignácio
• Orientador(a): Novais, Roberto Ferreira de
• Banca de defesa: Leite, Fernando Palha , Vergütz, Leonardus
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Mestrado em Solos e Nutrição de Plantas
• Departamento: Fertilidade do solo e nutrição de plantas; Gênese, Morfologia e Classificação, Mineralogia, Química,
• País: BR
• Palavras-chave em Português: Eucalipto; Hipóxia; Mn
• Palavras-chave em Inglês: Eucalyptus; Hypoxia; Mn
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO
• Link de acesso: http://locus.ufv.br/handle/123456789/5525

The Shoot Dieback of Eucalyptus in Vale do Rio Doce (Seca de Ponteiros do Eucalipto do Vale do Rio Doce - SPEVRD) is a physiological disorder which affects eucalyptus plantations in several regions of Brazil, whose causes are still not fully understood. The symptoms of this disorder occur in the transition from the rain season to the dry season, with higher incidence in areas with poor drainage and higher water table when preceded by an intense rainy season. In addition, the accumulation of Mn also seems to be related to SPEVRD, observing higher levels of this nutrient in plant leaves with symptoms. Thus, this proposal was aimed at understanding the possible initial causes of SPEVRD as well as identify possible physiological, enzymatic and, or, fermentation mechanisms that confer greater tolerance of Eucalyptus clone 2719 to this anomaly in relation to sensitive clone hybrid urograndis 1213. A hydroponic experiment was conducted with a factorial 2 x 2 x 2 with two clones (2719 and 1213), two concentrations of O2 (8 e 4 mg L-1) and two Mn (1,39 e 300 mg L-1) using three replicates in randomized block design. Seedlings around 40 day old were maintained in Clark nutrient solution for 30 days and then treatments were applied for 11 days. At the end, it was evaluated gas exchange rate and leaves and roots were collected. The hypoxia affected both clones reducing root dry matter production, but only the tolerant clone suspended leaf growth, keeping the proportion between leaves and roots similar regardless the treatment, while the sensitive clone had an increase in this ratio due to the decrease production of roots and maintenance of leaf growth. The sensitive clone had higher concentrations of Mn in young leaves compared to the tolerant one. In both clones, the photosynthesis rate and stomatal conductance were reduced by hypoxia, but the internal carbon concentration remained high, indicating biochemical limitations to photosynthesis. Due to the maintenance of chlorophyll contents, cellular damage can occur if the absorbed energy is not properly dissipated. These damages were proven by higher levels of malondialdehyde (MDA) in sensitive clone leaves, which increase was not observed in tolerant leaves. In leaves, although the superoxide dismutase (SOD) activity was higher in tolerant clone, both catalase activity and total antioxidant capacity were similar between clones, indicating that the tolerant clone probably has preventive mechanisms to avoid damage caused by reactive oxygen species (ROS) and not only detoxifing them. In roots, MDA levels were also higher in sensitive clone, especially in the treatment with excess of Mn. The tolerant one had a higher SOD activity and increased antioxidant capacity in roots. The activity of alcohol dehydrogenase (ADH), alanine transaminase (AlaT) and aspartate transaminase (AspT) were increased under hypoxia, with the highest elevation of ADH in the sensitive clone which demonstrates to have an increased metabolism, which explains, at least partially, the greater damage. The tolerant clone activates characteristic responses of quiescence, resulting in greater survival of deep roots in hypoxic conditions. Taken together, this response of the tolerant clone to SPEVRD may also increase tolerance to drought, avoiding damage and nutritional disorders that can lead to appearance of symptoms of SPEVRD. On the other hand, the sensitive clone has escape responses to hypoxia, which can confer increased susceptibility to drought, as well as to excess of Mn in leaves and potential damage that can initiate processes which cause this anomaly.