Arsenic (As) pollution is a major environmental concern due to its worldwide distribution and high toxicity to organisms. The fern Pityrogramma calomelanos is one of the few plant species known to be able to hyperaccumulate As, although the mechanisms involved are largely unknown. This study aimed to investigate the metabolic adjustments involved in the As-tolerance of P. calomelanos. For this purpose, ferns with five to seven fronds were exposed to a series of As concentrations. Young fronds were used for biochemical analysis and metabolite profiling using gas chromatography-mass spectrometry. As treatment increased the total concentration of proteins and soluble phenols, enhanced peroxidase activities, and promoted disturbances in nitrogen and carbon metabolism. The reduction of the glucose pool was one of the striking responses to As. Remarkable changes in amino acids levels were observed in As-treated plants, including those related to biosynthesis of glutathione and phenols, osmoregulation and two photorespiratory intermediates. In addition, increases in polyamines levels and antioxidant enzyme activities were observed. In summary, this study indicates that P. calomelanos tolerates high concentration of As due to its capacity to upregulate biosynthesis of amino acids and antioxidants, without greatly disturbing central carbon metabolism. At extremely high As concentrations, however, this protective mechanism fails to block reactive oxygen species production, leading to lipid peroxidation and leaf necrosis.

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Pityrogramma calomelanos is interestingly the single non-Pteris arsenic (As)-hyperaccumulating fern. It has been pointed as a potential species for phytoremediation and a model plant to study the As toxicity and its mechanisms of action. In order to investigate the morphoanatomical traits associated to As tolerance, P. calomelanos plants were exposed to different As concentrations in hydroponic solution. At low As dose (1 mM As), 90% of the As accumulated in plants was allocated in shoots, and no symptoms of As stress were observed in fronds and roots. Under higher As exposure (10 and 30 mM As), 81-74% of the total As in plants was present in shoots, and apical and marginal necroses on pinnae were observed. Anatomical observations showed that As induces damages mainly in the secondary veins and adjacent cells. High amounts of phenols were observed in pinna tissues of control and treated plants. In the roots, As promoted slight alterations as detachment of border-like cells and accumulation of granular substances in cortical cells. The high root-to-shoot As translocation and the constitutive presence of phenols and border-like cells protecting the root tips showed to be adaptive traits that allow P. calomelanos to survive in contaminated sites.

Arsenic (As) hyperaccumulation trait has been described in a limited number of fern species. The physiological basis of hyperaccumulation remains unclear, especially in non-Pteris species such as Pityrogramma calomelanos. Aiming at a better understanding of As-induced responses, P. calomelanos plants were exposed to 1 mM As for 21 days and compared with control plants. Chemical analyses revealed that As accumulation was ten times higher in pinnae then in roots and stipes. In pinnae, As was present mainly as arsenite, whereas arsenate was the dominant form in stipes and roots. Arsenic promoted an increase in antioxidant enzyme activities in both fern parts and several alterations in mineral nutrition, especially with regard to P and K. A higher content of non-protein thiols was observed in pinnae of plants exposed to As, whereas As induced the increase in lipid peroxidation in roots. The results showed that Pityrogramma calomelanos shares with Pteris vittata several aspects of As metabolism. High root-shoot As translocation showed to be essential to avoid toxic effects in roots, since the root is more sensitive to the metalloid. The higher capacity of P. calomelanos to sequester arsenite in the pinna and its efficient antioxidant system maintain the reactive oxygen species at a low level, thus enhancing the continuous accumulation of As. Molecular investigations are needed to elucidate the evolution of As-tolerance mechanisms in Pteridaceae species, especially with regard to membrane transporters and ROS signaling.

Arsenic (As) is toxic to most living things. However, plants growing in environments contaminated by this pollutant may exhibit tolerance strategies such as restrictions to its absorption and intracellular detoxification. In the present study we compared morphophysiological responses between Borreria verticillata (L.) G.F.W. Mayer (Rubiaceae) populations from an As-contaminated site (CS) and a non-contaminated site (NCS) in order to clarify their mechanisms of As detoxification and their differential tolerance to the metalloid. Plants were grown in nutrient solution without As addition (control) and with 66 µM As for 4 days. Arsenic accumulated in plant roots, and neither bioaccumulation nor translocation factors differed between the populations. Exposure to the metalloid promoted damage to the morphology and anatomy of both roots and shoots, particularly in plants from the NCS. These plants showed more severe phytotoxic symptoms, as well as greater reduction in shoot growth and fresh biomass accumulation. Plants from the CS showed fewer toxicity symptoms due to mechanisms that favoured As detoxification and scavenging of reactive oxygen species in roots (e.g. increases in Ca and S root concentrations, higher number of phenolic and crystalliferous idioblasts and increased antioxidant enzyme activity) and the prevention of oxidative stress in leaves (through increased superoxide dismutase activity). Thus, we verified that besides the differences in P metabolism that have been reported in the literature, plants from the CS are more As-tolerant due to their higher efficiency for As detoxification, and are therefore more well suited for the revegetation of As-contaminated areas.

Studies on pollutant accumulation in plants are essential for the diagnosis of species with potential for revegetation and remediation of contaminated environments. Hydroponic systems are commonly used for this purpose, but little is known about the influence of the nutrient solution in the results. Borreria verticillata can be found in arsenic (As)-contaminated environments, and research using Hoagland's nutrient solution has reported a differential tolerance to the metalloid in populations from contaminated (CS) and non-contaminated (NCS) sites. However, some authors suggest the use of Clark's solution to study As tolerance in plants. We evaluated the growth and nutritional status of plants from these populations, cultivated in Hoagland's and Clark's solutions, and determined the most appropriate solution for comparative studies on tolerance to As. The selected solution was used in plant cultivation for As exposure. In Hoagland's solution plants from the NCS exhibited higher root volume, fresh and dry weight and macronutrient accumulation than those from the CS. Clark's solution promoted more similar responses and was used in plant exposure to 0, 33 and 66 lM As, for 4 days. The metalloid promoted reduction of total fresh weight in both populations. Alterations were more severe on plants from the NCS, with decreased values of root volume, gas exchanges, height and nutrient concentration in shoots. The severe damage caused by As in plants from the NCS demonstrates its sensitivity to this metalloid, while the responses of the CS population confirm the As-tolerance. These findings suggest that these populations are different ecotypes of B. verticillata.

RESUMO O estudo da fitoterapia tem se tornado muito importante na atualidade, uma vez que possibilita a descoberta de novas substâncias com potencial medicinal e industrial. Dentro desse contexto, a sabedoria popular proveniente da transmissão dos conhecimentos tradicionais entre as gerações desempenha um papel fundamental. O objetivo desse trabalho foi realizar um levantamento das plantas com finalidade medicinal utilizadas pelas famílias do Assentamento Madre Cristina, em Ariquemes (RO), contribuindo para o conhecimento e a valorização da sabedoria popular. Para isso, foram realizadas entrevistas com famílias residentes no Palavras-chave: Conhecimento popular, Plantas medicinais, Comunidades rurais.