Iron Toxicity on Germination and Early Growth of Cecropia hololeuca Miq.

O ferro (Fe) e um nutriente essencial para as plantas, sendo insubstituivel ao metabolismo. Todavia, o aumento em sua concentracao leva ao acumulo de especies reativas de oxigenio e estresse oxidativo que resultara em prejuizos aos vegetais. O objetivo deste trabalho foi verificar o efeito de elevadas concentracoes de Fe na germinacao e desenvolvimento de Cecropia hololeuca Miq. A especie foi submetida as concentracoes de 0,045, 4 e 8mM aplicados na forma de sulfato ferroso e Fe-EDTA. Foram analisadas a porcentagem de germinacao, indice de velocidade de germinacao, comprimento da parte aerea, radicular, massa fresca e seca. Para a analise de desenvolvimento foi analisado a area folhar o comprimento do caule, comprimento radicular, massa fresca e seca, os pigmentos cloroplastideos, fluorescencia da clorofila, e analise dos teores de elementos via EDS. Foi verificado a atividade enzimatica (SOD, CAT, POX). Ambas as fontes de Fe resultaram em danos a germinacao e desenvolvimento. O tratamento com Fe-EDTA mostrou efeitos mais significativos na germinacao, crescimento aereo e radicular e biomassa das sementes. O mesmo tratamento se mostrou mais prejudicial nas plântulas jovens com quedas na clorofila a, crescimento radicular, aereo, area folhar e biomassa. As plântulas expostas ao Fe apresentaram queda no desempenho fotossintetico e no teor de calcio (Ca) folhar. Nao foi observado aumento na atividade da CAT e SOD. A POX apresentou elevacao quando submetida ao Fe-EDTA 8mM. Tais resultados evidenciam que a especie C. hololeuca se mostra sensivel a toxidez por ferro, acarretando danos ao metabolismo e crescimento inicial.    Palavras-chave: Embauba. Estresse. Metal Pesado. Toxidez.  Abstract Iron (Fe) is as an essential nutrient for plants and is irreplaceable in many metabolic processes. However, the increase in its concentration leads to the accumulation of reactive oxygen species and oxidative stress that will result in damage to plant. The objective of this work was to verify the effect of high Fe concentrations on germination and initial development of Cecropia hololeuca Miq. They were submitted to concentrations of 0.045, 4 and 8mM applied as ferrous sulfate and Fe-EDTA. Germination percentage, germination speed index, shoot length and root, fresh and dry mass were analyzed. For the initial developmental the following variables were analyzed: Leaf area, stem length, root length, fresh and dry mass, chloroplast pigments, chlorophyll fluorescence analysis, analysis of element contents via EDS. The activity of enzymes (SOD, CAT, POX) was verified. Both sources of Fe resulted in damage to germination and development. Fe-EDTA treatment showed the most significant negative effects on germination, root and air growth and seed biomass accumulation. The same treatment was more detrimental in the establishment of young seedlings with decreases in chlorophyll a, root growth, aerial growth, leaf area and biomass accumulation. Seedlings exposed to Fe showed a decrease in photosynthetic performance and a decrease in leaf calcium (Ca) content. No increase in CAT and SOD enzymes activity was observed. POX increased its activity when submitted to 8mM Fe-EDTA. These results show that the species C. hololeuca is sensitive when exposed to toxic levels of Fe, causing damage to metabolism and initial growth.   Keywords: Embauba. Stress. Heavy Metal. Toxicity.