Acúmulo, distribuição e eliminação de ferro em três espécies vegetais do manguezal
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Data
2016-02-26
Autores
Arrivabene, Hiulana Pereira [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A poluição por metais tem sido um dos principais problemas ambientais, tendo em vista a sua toxicidade, persistência no ambiente e bioacumulação. Os manguezais frequentemente são expostos a esses contaminantes, sendo o ferro um dos metais presentes em maior concentração no sedimento e com papel biogeoquímico importante quanto à precipitação e ciclagem de metais. Investigamos o acúmulo, a distribuição e a eliminação de ferro em Avicennia schaueriana Stapf & Leechm. ex Modenke, Laguncularia racemosa (L.) C.F. Gaertn. e Rhizophora mangle L. submetidas a diferentes concentrações de ferro. Para esse estudo, propágulos das três espécies estudadas foram coletados em campo e cultivados em meio nutritivo de Hoagland. Após o cultivo, as plantas foram submetidas a quatro tratamentos pela adição de 0 (controle), 10, 20 e 100 mg L-1 de Fe(II)SO4 no meio nutritivo. As plantas foram então coletadas, sendo realizadas análises químicas, anatômicas, histoquímicas e ultracitoquímicas. Parte dessas análises também foi feita em campo para comparação dos dados. Os resultados mostraram que a placa de ferro é local de grande acúmulo de ferro nessas plantas. L. racemosa foi a espécie que mais acumulou ferro em placa e raízes, enquanto A. schaueriana apresentou os níveis mais altos em caules e folhas. A bioacumulação de ferro em placa e raízes de L. racemosa aumentou progressivamente à medida que a concentração de ferro no substrato aumentou. A secreção de ferro por glândulas de sal ocorreu e foi fortemente inibida sob concentrações de ferro acima do controle em L. racemosa, enquanto em A. schaueriana não houve uma queda evidente entre controle e concentrações de ferro mais elevadas. Em geral, L. racemosa apresentou os menores fatores de translocação entre as três espécies estudadas. Com o aumento de ferro no substrato houve redução nos fatores de translocação de ferro entre partes aéreas e raiz e isso foi mais evidente em R. mangle. A maioria dos parâmetros analisados na anatomia radicular não mostrou diferença significativa entre os tratamentos. Os parâmetros que mostraram alterações foram espessura de raiz e córtex em A. schaueriana, com valores maiores em plantas controle, e espessura de raiz em L. racemosa, com valores menores em plantas expostas a 100 mg L-1. Para as três espécies estudadas, os principais locais de bioacumulação de ferro (Fe (II) e Fe (III)) em raízes foram principalmente a epiderme, mas também o córtex. A bioacumulação de ferro em caules e folhas foi diferente para cada espécie. Em caules, o câmbio vascular de L. racemosa e a periderme de R. mangle foram os principais locais de acúmulo. Por outro lado, em A. schaueriana não foi possível identificar os principais locais. Em folhas, o ferro foi detectado principalmente no parênquima aquífero de A. schaueriana e no xilema de L. racemosa. Ambas as espécies também mostraram acúmulo de ferro em glândulas de sal. Em R. mangle, a bioacumulação foliar de ferro ocorreu em diversos tecidos, sobretudo o parenquimático. Análises de material vegetal fresco, recém coletado em campo, mostraram que glândulas de sal de A. schaueriana e L. racemosa também exibem reação histoquímica positiva quando testada com o reagente de Perl, indicando acúmulo de ferro. Além disso, ultracitoquimicamente e usando o mesmo marcador específico, o ferro foi localizado em células secretoras, aderido à membrana de vacúolos e a plasmodesmas. Em ambas as espécies residentes em campo, a presença de ferro na secreção foi confirmada por meio de análise química. Ao nosso conhecimento, este é o primeiro estudo detalhado sobre a resposta de plantas de manguezal a concentrações crescentes de ferro sob condições controladas.
Metal pollution has long been one of the major environmental problems due to its toxicity, environmental persistence and bioaccumulation. Mangroves are often exposed to these contaminants, and iron is one of the metals present in higher concentrations in sediments and has an important biogeochemical role as regards the precipitation and cycling of metals. We investigate the iron accumulation, distribution and elimination in Avicennia schaueriana Stapf & Leechm. ex Modenke, Laguncularia racemosa (L.) CF Gaertn. and Rhizophora mangle L. exposed to different concentrations of iron. For this study, propagules of all species were collected in field and were cultivated in Hoagland’s nutritive medium. After growing, plants were exposed to four treatments by adding 0 (control), 10, 20 and 100 mg L-1 of Fe(II)SO4 to the nutritive medium. Then, plants were collected and chemical, anatomical, histochemical and ultracitochemical analysis were carried out. Part of these analyses was also made in the field for data comparison. The results showed that the Fe-plaque is a place of high iron accumulation in these plants. L. racemosa accumulated the highest amounts of iron in the plaque and roots, while A. schaueriana presented the highest levels in stems and leaves. The bioaccumulation of iron in plaque and roots of L. racemosa increased progressively as the added-iron concentration rose. The iron secretion through salt glands occurred and it was strongly inhibited in L. racemosa at iron concentrations above controls, while A. schaueriana did not show a noticeable drop from controls to the highest added-iron concentration used. In general, L. racemosa presented the lowest translocation factors among the three studied species. With the increase of iron in the substrate, there was a drop in translocation factors between aerial parts and root, and that was more evident in R. mangle. Most analyzed parameters in root anatomy did not show significant changes throughout iron concentrations. The parameters showing changes were the thickness of cortex and root in A. schaueriana, with higher values in controls, and thickness of root in L. racemosa, with lower values in plants exposed to 100 mg L-1. The main places of iron bioaccumulation (Fe(II) and Fe(III)) in roots were mainly the epidermis, but also cortex, in the three studied species. The bioaccumulation of iron in stems and leaves was different for each species. In stems, the vascular cambium of L. racemosa and the periderm of R. mangle were the main places for accumulation. Conversely, in A. schaueriana it was not possible to verify the main places. In leaves, iron was mostly detected in water storage parenchyma of A. schaueriana and in xylem of L. racemosa. Both species also showed accumulation of iron in salt glands. The leaf bioaccumulation in R. mangle occurred in several tissues, mainly the parenchyma. Fresh plant material analysis, recently sampled in field, shown that salt glands from A. schaueriana and L. racemosa had positive histochemical reaction when tested with Perl’s reagent, indicating iron accumulation. Additionally, ultracitochemistry, using the same specific marker, showed that iron was in secretory cells, adhered to the membrane of vacuoles and to plasmodesmata. In both species resident in field, the presence of iron in the secretion was confirmed by chemical analysis. To our knowledge, this is the first detailed report on the response of mangrove plants to increasing iron concentrations under controlled conditions.
Metal pollution has long been one of the major environmental problems due to its toxicity, environmental persistence and bioaccumulation. Mangroves are often exposed to these contaminants, and iron is one of the metals present in higher concentrations in sediments and has an important biogeochemical role as regards the precipitation and cycling of metals. We investigate the iron accumulation, distribution and elimination in Avicennia schaueriana Stapf & Leechm. ex Modenke, Laguncularia racemosa (L.) CF Gaertn. and Rhizophora mangle L. exposed to different concentrations of iron. For this study, propagules of all species were collected in field and were cultivated in Hoagland’s nutritive medium. After growing, plants were exposed to four treatments by adding 0 (control), 10, 20 and 100 mg L-1 of Fe(II)SO4 to the nutritive medium. Then, plants were collected and chemical, anatomical, histochemical and ultracitochemical analysis were carried out. Part of these analyses was also made in the field for data comparison. The results showed that the Fe-plaque is a place of high iron accumulation in these plants. L. racemosa accumulated the highest amounts of iron in the plaque and roots, while A. schaueriana presented the highest levels in stems and leaves. The bioaccumulation of iron in plaque and roots of L. racemosa increased progressively as the added-iron concentration rose. The iron secretion through salt glands occurred and it was strongly inhibited in L. racemosa at iron concentrations above controls, while A. schaueriana did not show a noticeable drop from controls to the highest added-iron concentration used. In general, L. racemosa presented the lowest translocation factors among the three studied species. With the increase of iron in the substrate, there was a drop in translocation factors between aerial parts and root, and that was more evident in R. mangle. Most analyzed parameters in root anatomy did not show significant changes throughout iron concentrations. The parameters showing changes were the thickness of cortex and root in A. schaueriana, with higher values in controls, and thickness of root in L. racemosa, with lower values in plants exposed to 100 mg L-1. The main places of iron bioaccumulation (Fe(II) and Fe(III)) in roots were mainly the epidermis, but also cortex, in the three studied species. The bioaccumulation of iron in stems and leaves was different for each species. In stems, the vascular cambium of L. racemosa and the periderm of R. mangle were the main places for accumulation. Conversely, in A. schaueriana it was not possible to verify the main places. In leaves, iron was mostly detected in water storage parenchyma of A. schaueriana and in xylem of L. racemosa. Both species also showed accumulation of iron in salt glands. The leaf bioaccumulation in R. mangle occurred in several tissues, mainly the parenchyma. Fresh plant material analysis, recently sampled in field, shown that salt glands from A. schaueriana and L. racemosa had positive histochemical reaction when tested with Perl’s reagent, indicating iron accumulation. Additionally, ultracitochemistry, using the same specific marker, showed that iron was in secretory cells, adhered to the membrane of vacuoles and to plasmodesmata. In both species resident in field, the presence of iron in the secretion was confirmed by chemical analysis. To our knowledge, this is the first detailed report on the response of mangrove plants to increasing iron concentrations under controlled conditions.
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Palavras-chave
Glândulas de sal, Histoquímica, Manguezal, Poluição por ferro, Ultraestrutura