Phytochelatin signal tranduction and cadmium chelation in plants

As plantas utilizam diversas estratégias de sinalização para reconhecer e responder aos stresses ambientais. A maioria das vias de transdução de sinais partilham um sinal genérico, normalmente a modulação dos níveis intracelulares de Ca2+. Esta por sua vez pode iniciar uma cascata de fosforilação proteica que finalmente afecta as proteínas directamente envolvidas na protecção celular ou culmina em factores de transcrição que vão determinar a resposta fisiológica ao stresse. A percepção destes sinais e a compreensão de como estes podem activar as respostas adaptativas são factores-chave para a tolerância das plantas a stresses abióticos. Um dos principais stresses abóticos que restrigem o crescimento das plantas é a presença de metais pesados. A produção de fitoquelatinas e a subsequente quelação dos metais é o mecanismo mais conhecido de tolerância ao stresse metálico em plantas. Fitoquelatinas (PCs) são péptidos com grupos tiol que são sintetizados através da transpeptidação da glutationa (GSH), pela acção da enzima fitoquelatina sintase (PCS). No entanto, até ao momento, as vias de sinalização que levam à síntese de fitoquelatinas e à percepção do stresse metálico são pouco compreendidas. Dentro deste contexto, o presente trabalho foi elaborado com o intuito de elucidar a via de sinalização através da qual o cádmio é detectado pelas células vegetais e induz a síntese de PCs. Quase todos, os estudos de stresses abióticos em plantas apontam para o facto de a sua sinalização se basear nos mesmos tipos de sinais moleculares, nomeadamente a sinalização por cálcio, a fosforilação proteica e a indução de espécies reactivas de oxigénio (ROS). Trabalhos recentes sugerem que a sinalização de PCs poderá envolver todos estes parâmetros. Assim, uma primeira abordagem foi efectuada para compreender a síntese de PCs na espécie Arabidopsis thaliana, através da monitorizaçção da actividade de enzimas relacionadas, a γ-EC sintetase, GSH sintetase e a PC sintase (PCS), assim como o tempo necessário para o elongamento das PCs e a sua acumulação. Seguidamente, ao longo deste processo foi analisada a expressão de sinais específicos, associados com sinais de cálcio, fosforilação proteica e sinalização por ROS. A importância destes factores na síntese de PCs foi também avaliada através do uso de moduladores farmacológicos de cálcio e fosfatases proteicas e também pela indução de stresse oxidativo. Os resultados demonstraram novos dados sobre o papel do cálcio e da fosforilação proteica na produção de PCs e na síntese de GSH, revelando que a actvidade da PCS é regulada por fosforilação e que a sinalização de cálcio pode mediar a síntese de GSH. O envolvimento da sinalização de ROS na síntese de GSH, atráves de crosstalk com a sinalização de cálcio também foi proposta. Assim, os resultados aqui apresentados descrevem uma possível via de sinalização de cádmio nas plantas e da indução de fitoquelatinas. Este trabalho poderá ser portanto muito útil na implementação de novas metodologias de agricultura sustentável e práticas de fitorremediação em solos contaminados com metais pesados.

Brazilian savanna forest : conservation, medicinal reservoir and bioprospecting

This study aimed to analyse the Brazilian savanna forest from a Legal Reserve (LR) area from a perspective of conservation, reservoir of organic carbon and medicinal biomass for a prospective use of native medicinal plants. An ethnobotanical and ethnopharmacological survey was carried out close to a community settled in the rural area in the south of Tocantins, being selected 9 of the most cited species (cajuí- Anacardium othonianum; inharé-Brosimum gaudichaudii; jatobá-Hymenaeae courbaril; jenipapo-Genipa americana, aroeira-Myracrodruon urundeuva; negramina-Siparuna guianensis; barbatimão- Stryphnodendron obovatum; assa peixe-Vernonia brasiliana, embaúba-Cecropia pachystachya). Crude foliar extracts were subjected to a preliminary phytochemical prospection and triage of secondary metabolites with antimicrobial activity of potential interest in health and familiar agriculture. Phenolic compounds, terpenes and flavonoids were detected in the extracts of most species, which suggests the presence of antimicrobial, antioxidant and anti-insect activities. It was evident the need to better know the LR as a reservoir of medicinal biomass in an area under ecological tension where 35% (610ha) of the property is LR and should be protected by law. Therefore, a forest inventory of live woody species was performed using the allometric or indirect method. This identified a rare remnant of Semidecidual Seasonal Forest amidst the largest world savannah, the Cerrado biome. An analysis of the forest average productivity per basal area (m².ha), aerial live biomass (ton.ha-1) and carbon stock was carried out. The forest fragment was considered relatively rich in species and diversity, although showing signs of disturbance and dominance by a few species. Its horizontal structure suggests biotic regeneration conditions. It is an important reservoir of medicinal plants. Of the families (57.5%) presenting medicinal species, 19 from a total of 33 are represented in the area and contain 44% (27) of the total species (61) and 63% (432) of the total individuals catalogued. Medicinal species have ecological importance for the equilibrium of the local flora and represent 80% of the 10 species with higher Importance Value Index (IVI): Tetragastris altissima, Chrysophyllum marginatum, Oenocarpus distichus, Sclerolobium paniculatum, Simarouba versicolor, Alibertia macrophylla, Siparuna guianensis, Maprounea guianensis, Licania parvifolia e Physocalymma scaberrimum. Medicinal productivity was high for this type of phytophysionomy: 183,2 ton. ha-1 of biomass and 91,51 ton. ha-1 of carbon representing 66% of the total biomass and carbon of this Cerrado forest. From this stage S. guianensis (Siparunaceae) was selected for performing bioassays in order to verify its biological activity against microorganisms of health and agricultural relevance. This is a native aromatic medicinal plant recommended as priority for conservation, with local popular medicinal validation and availability of medicinal feedstock (3300 Kg.ha-1), with the foliar fraction giving 38Kg/ha of crude extract and 5L/ha of essential oil. Foliar crude extracts and essential oil were obtained and tested in vitro using a disk diffusion bioassay. Different concentrations of these natural products were tested against gram-positive bacteria (Staphylococcus aureus ATCC 29213), gram-negative bacteria (Escherichia coli ATCC 25922 and ATCC 35218; Pseudomonas aeruginosa ATCC 10145) and fungi (Candida albicans ATCC 6258 e Fusarium oxysporum). The essential oil inhibited the growth of S. aureus in its crude concentration (380μg.mL-1), as well as diluted to half (190μg.mL-1) and a quarter strength (95μg.mL-1). It’s likely that such action is due to sesquiterpenes major components, such as bisabolol and bisabolene (10.35%), measured by gas chromatography (GC-MS, GC-FID). Extracts did not exhibit any antimicrobial activity against the microorganisms tested. The native medicinal plants prospective market is an alternative that favours the conservation of biodiversity while generating benefits for the development of sustainable family productive activities within local ecosystems instead of the current inappropriate uses. This strengthens conservation policies of Legal Reserve in rural settlements and is in agreement with public policy on global warming and climate changes.

Metais em plantas e algas : acumulação e potencial aplicação em processos de remediação

The present work reports the study of the bioaccumulation of potentially toxic elements (cadmium, lead and mercury) by marine macroalgae (Ulva lactuca, Fucus vesiculosus and Gracilaria gracilis), abundant in the coast and estuarine systems worldwide. These organisms proved to be capable of withstanding moderate multi-metallic contamination (environmentally relevant concentrations), incorporating high amounts of metal in their tissues. The high removal percentages achieved, in particular for mercury (99%), demonstrate the potential of these algae as a basis for a new biotechnological treatment of saline waters contaminated with metals (more efficient, cost-effective and environmentally friendly than conventional methods). U. lactuca was considered the most promising due to the better performance presented. The comparison between the bioaccumulation and biosorption processes suggested that in some cases the use of the living organism will have advantages over the application of biomass, due to the simplicity of the overall process, and the lower residual concentration of metal achieved in the solution (especially for Cd). The transfer and accumulation of Hg by terrestrial plants (Brassica juncea and Lolium perenne) in agricultural fields near a contaminated industrial area was also studied. Despite the low bioaccumulation factors found (<1), there were high Hg content in plants (up to 84 mg kg-1 in roots and up 6.9 mg kg-1 in shoots, dry weight). Daily intake estimates for grazing animals (cows and sheep) pointed to the potential risk to human health derived from consumption of their meat. The results highlighted the important role that plants and algae may have in protection, risk assessment and remediation of environmental systems contaminated with metals.