Aluminum concentration, nutritional status and metabolite profile in native Cerrado species with different resistance strategies to the metal

• Ano de defesa: 2017
• Autor(a) principal: Silva, Samara Arcanjo e
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Solos ácidos; Química do solo; Alumínio - Resistência de materiais; Plantas dos cerrados; Cerrados; Botânica
• Link de acesso: http://www.locus.ufv.br/handle/123456789/21133

Aluminum (Al) is the most abundant metallic element in the Earth crust. Its toxicity not only depends on the total Al concentration in the soil, but also on the Al chemical form, which is highly dependent on soil pH. In acid soils (i.e., having pH lower than 5.5), Al is solubilized and toxic forms like Al 3+ (exchangeable Al) are then released into the rhizosphere, interfering with root growth and functions and limiting crop productivity. Despite that, natural vegetation that grows on acid soils, such as the ones from the Cerrado, has developed strategies to cope with high Al 3+ concentrations, but unfortunately, research focusing on the Al resistance mechanisms of plant species therein are still scarce. In this study, we tested the hypothesis that Al resistance strategies are constitutive features and do not depend on the concentration of the metal in soils. For that, we determined the shoot Al concentration and Al deposition sites in plants of Eugenia dysenterica, Qualea parviflora, and Q. multiflora, all native Cerrado species naturally growing on acid soils with varying fertilities and metal toxicities. Nutritional and metabolic adaptations of the plants were also analyzed. Aluminum and nutrient concentrations in soil samples were determined by energy dispersive X-ray microfluorescence (μEDXRF), while in plant samples they were evaluated by both inductively coupled plasma atomic emission spectrometry and μEDXRF. Al mapping in plant samples was performed by histochemical test, X-ray probe coupled to scanning electron microscopy, and μEDXRF. Metabolic adaptations were assessed by spectrophotometric analyses and gas chromatography–mass spectrometry. E. dysenterica accumulated about 0.5 g Al kg -1 DW in the shoot. In contrast, concentrations of the metal in shoots of Q. parviflora and Q. multiflora were up to 15.0 and 20.0 g Al kg -1 DW, respectively, at all collection sites. Q. parviflora was able to hyperaccumulate Al even on a soil with negligible Al +3 concentration. Pectocellulosic cell walls were the preferential sites for Al deposition, but the metal was also localized in suberized cell walls and in chloroplasts. Al concentration in the species showed different correlations with soil chemical attributes. In Q. parviflora and E.dysenterica, it was positively correlated with mesotrophic soils while in Q. multiflora it was positively correlated with dystrophic ones. In general, nutrient levels in E. dysenterica were lower and more influenced by concentration of total Al in the soil, yet no nutritional deficiency was observed. The levels of K, P, and S in Q. multiflora were increased in plants with highest Al accumulation. Metabolite analyses demonstrated that the levels of chlorophyll, nitrate, total amino acids, insoluble proteins, phenols, and thiobarbituric acid-reactive substances were higher in leaves of E. dysenterica. In contrast, Q. parviflora had higher non-protein thiol concentration and was more efficient in avoiding lipid peroxidation. The synthesis of compatible osmolytes and dehydroascorbate was up-regulated in both species on soils with high metal toxicity. Q. parviflora also showed increased levels of malate and succinate. Altogether, these findings confirm the hypothesis that neither the non-accumulator nature of E. dysenterica nor the Al-hyperaccumulator nature of both Qualea species depends on Al concentration in soils, and support the theory that species adapted to acid soils have mechanisms to cope with Al toxicity and avoid Al-induced nutritional deficiency. Q. parviflora, in especial, seems to have mechanisms for altering Al availability in the soil, which enables the species to hyperaccumulate Al even on a soil with negligible Al +3 concentration. The results on metabolic adaptations reinforce the hypothesis that phenols, thiols, and organic acids are all involved in the detoxification of Al and reactive oxygen species (ROS) in Al-hyperaccumulator species. On the other hand, the metabolic adaptations involved in ROS scavenging in E. dysenterica, such as phenol and dehydroascorbate production, were not sufficient to control oxidative stress in plants growing on soils with high metal toxicity.