Search

Purposes To analyze the main edaphic factors that differentiate ultramafic from typical Cerrado environments and act as agents of the development of biochemical and morphological mechanisms of species adaptation to these harsh environments; and to determine the genetic diversity of three Cerrado’s shrubland native species (Justicia lanstyakii, Euploca salicoides, and Oxalis hirsutissima). Methods We conducted chemical analysis of metal contents in soils, as well as on elemental composition, and analysis of DNA extracted from leaf tissues of the three species found in both environments. In leaves of E. salicoides grown in both environments we evaluated the changes in the levels of non-structural carbohydrates (NSC), and total proteins. Results The accessions obtained in ultramafic soils were closer with each other, indicating genetic similarity and major differences in relation to the accessions collected in the Cerrado area. These differentiations probably are related with higher adaptation to soils rich in metals, mainly Ni in ultramafic, and Al in the Cerrado environments. The highest levels of NSC were observed in plants grown in ultramafic soils, including raffinose, which is related to responses to metal detoxification and drought. The allocation of Ni in the trichomes, which does not affect important processes of plant metabolism, is another mechanism developed by E. salicoides to overcome the hyperaccumulation of Ni in their tissues. Conclusions These findings can help select seed collection sites representative of the genetic diversity of native plant species for restoring degraded areas or for phytoremediation of metals.

Soils derived from ultramafic rocks have a mineralogy rich in metals like Co, Cr, Fe and Ni, and the process of extracting these metals from soil generates highly metallic waste. When disposed near of water bodies these residues pose a risk on the aquatic environment. Two fish species are used in ecotoxicity tests worldwide: Danio rerio (zebrafish), an Asian species, and Oreochromis niloticus (tilapia), an African one. However, Hyphessobrycon eques (mato grosso), a native of South America and found in Brazilian rivers, is as yet little used in ecotoxicity tests. The aims of this study were to evaluate the acute toxicity of the metals Co, Cr, Fe and Ni to the fish D. rerio, O. niloticus and H. eques, and compare its susceptibility. Tests were conducted following the recommendations of the Brazilian Association for Technical Standardization (ABNT). Stock solutions were prepared with the analytical reagents CoCl2.6H2O; K2Cr2O7; FeCl3.6H2O e NiCl2.6H2O. The quantification of metals was carried out in the stock solutions by ICP-AES. The dilution water used was synthetic softwater pH 7.3±0.1, hardness 43 mg L-1; DO 95% and temperature 25±1°C. To perform static tests 10 fish from each species were exposed for 96 hours, in duplicate, to different concentrations of the metals tested. The measured 96-hr initial lethal concentrations LC(I)50 of metals Co, Cr, Fe and Ni, calculated by the Trimmed Spearman Karber method, were 35.7, 35.9, 5.6 and 15.0 mg L-1 for D. rerio, 79.8, 32.6, 8.8 and 49.7 mg L-1 for O. niloticus and 104.1, 23.7, 8.5 and 34.5 mg L-1 for H. eques, respectively. The data showed that D. rerio has greater susceptibility to the metals tested, which justifies its increased use as a test species, except concerning Cr, for which H. eques was the most sensitive species.

We investigated the pattern of aluminum (Al) accumulation in leaf tissues of native hyperaccumulator Vochysiaceae species Qualea grandiflora, Callisthene major, and Vochysia pyramidalis, from the Brazilian Cerrado. Non-accumulator Sclerolobium paniculatum was used as a control species. We expected a strong compartmentalization of Al in non-active leaf cell compartments such as cell walls and vacuoles in Al-accumulating species and the absence of Al in critical metabolic sites such as the chloroplasts. Plant leaves were harvested in the field and cut in small segments for histological analysis; hematoxylin dye was used for Al localization in tissues. Results of soil analysis of the three sites and the concentration of Al in leaves indicated that there is no direct relationship between Al availability in soils and Al hyperaccumulation among the Vochysiaceae species evaluated. The cross-sections of leaf tissues showed hematoxylin color in the palisade and spongy parenchyma cells (chloroplast) of Q. grandiflora and C. major. The vascular system of Q grandiflora was not colored, but some cells from the xylem region of C. major were stained. In contrast, the adaxial and abaxial epidermal cells of V. pyramidalis were colored by hematoxylin, as were some cells from the vascular bundle, but color formation was not observed in the cells of palisade parenchyma. Al was not detected in leaves of S. paniculatum. We concluded that, although hyperaccumulation of Al is a common trait in the Vochysiaceae family, the processes of storage and detoxification in leaf tissues differ among the species. Two of the three hyperaccumulator species use chloroplasts as a sink for Al, with no apparent signs of toxicity. Therefore, the physiological role of Al in plant tissues remains to be elucidated. (C) 2010 Elsevier B.V. All rights reserved.

Ultramafic soils are characterized by high levels of metals, and have been studied because of their geochemistry and its relation to their biological component. This study evaluated soil microbiological functioning (SMF), richness, diversity, and structure of bacterial communities from two ultramafic soils and from a non-ultramafic soil in the Brazilian Cerrado, a tropical savanna. SMF was represented according to simultaneous analysis of microbial biomass C (MBC) and activities of the enzymes β-glucosidase, acid phosphomonoesterase and arylsulfatase, linked to the C, P and S cycles. Bacterial community diversity and structure were studied by sequencing of 16S rRNA gene clone libraries. MBC and enzyme activities were not affected by high Ni contents. Changes in SMF were more related to the organic matter content of soils (SOM) than to their available Ni. Phylogeny-based methods detected qualitative and quantitative differences in pairwise comparisons of bacterial community structures of the three sites. However, no correlations between community structure differences and SOM or SMF were detected. We believe this work presents benchmark information on SMF, diversity, and structure of bacterial communities for a unique type of environment within the Cerrado biome.

TitleLocalization of Aluminum in Root Tip Tissues of Wheat VarietiesDiffering in Aluminum ToleranceAuthor(s) Andrade, Leide R. M. de; Ikeda, Motoki; Ishizuka, JunjiCitation九州大学農学部紀要 ¦¦ 41(3/4) ¦¦ p151-156; Journal of the Faculty ofAgriculture, Kyushu University ¦¦ 41(3/4) ¦¦ p151-156Issue Date 1997-03URL http://hdl.handle.net/2324/24140Right

Extract As previously reported (Taylor and Foy 1985; Keltjens and Ulden 1987; Grauer and Horst 1990; Galvez and Clark 1991), plant species and varieties widely differ in Al tolerance. Although many hypotheses about the physiological mechanism(s) involved in Al tolerance have been formulated, the mechanism(s) has not been elucidated. However, it is obvious that when exposed to Al at high concentrations, Al-tolerant plants seem to be able to avoid the toxicity by refraining from excess uptake of Al or by chelating of Al in the rhizosphere or in the roots. In such ways, Al can not affect the growth of tolerant plants (Foy et al. 1978).

The effects of aluminium (Al) on the metabolism of organic acids synthesised via nonphotosynthetic carbon fixation in the roots and on malate exudation were investigated in Al-tolerant Shirosanjyaku (SH) and Al-sensitive Chikushikomugi (CK) wheat cultivars labelled with bicarbonate-14C. Aluminum triggered the excretion of 14C into the solution, especially in the SH that excreted 2.5 times more 14C than the CK. The loss of radioactivity (about 10%) into the solution represented a small drain in the 14C reserve found in the roots. In the organic acid fraction within the roots, malate contained the greatest amount of 14C, and this amount decreased rapidly with time in both cultivars. The disappearance of radioactivity in the malate resulted from metabolism and translocation rather than to root efflux. Aluminium decreased the malate concentrations in roots of both cultivars. The Al-sensitive cultivar had higher concentrations of malate regardless of the presence of Al. It was therefore assumed that the decrease of malate concentration in roots under Al stress did not result from the decline in malate synthesis but due to an increase in malate decomposition. This response was interpreted as the result of the Al-induced stress and not as the cause of a differential Al-tolerance between the wheat cultivars. An important component of the differential Al tolerance between SH and CK is the greater ability of the Al-tolerant cultivar to excrete malate from the roots, which is independent of its internal concentration in the roots.

Trabalho apresentado no 29o. Congresso Brasileiro de Fitopatologia. Resumo 168.