| Resumo: |
Mangroves are ecosystems of great economic, ecological and social importance. However, these environments have been severely contaminated by waste and effluents containing metals and metalloids. In plant tissues, the accumulation of these contaminants is determined by their sediment bioavailability and by plant efficiency in absorbing and transporting them through the roots and vascular tissues. Therefore, it is essential to investigate the impact of these contaminants on the development of mangrove plant species. Two mangrove areas located in the state of Maranhão were selected: [1] Mangue Seco Beach (Raposa municipality), an area considered partially preserved, and [2] the Itaqui Port (São Luís capital), considered a large industrial hub and one of the largest port areas in Brazil. The research quantified and analyzed the different metals, metalloids and oxidative stress biomarkers , seeking to compare their effects at the anatomical level in Rhizophora mangle (Rhizophoraceae), Laguncularia racemosa (Combretaceae) and Avicennia germinans (Acanthaceae) leaves. Young and expanded leaves were collected in loco, seeking to maintain uniformity in size and absence of chlorosis. At each sampling point, 10 leaf samples were collected from five individuals of each species for analysis of metals and biomarkers, where they were subjected to the ANOVA test and Dunn’s multiple comparisons test using the free software R. For the anatomical analyses, five leaf samples from three individuals of each species were collected, ten fields from six individuals were used to measure the thickness of the cells and tissues, the data means were subjected to the Student's t-test for independent samples using the Jamovi statistical program. The analyzed metals and metalloids were: Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, Ti, V and Zn. Statistically significant differences (p<0.05) and high levels of Fe, Al, Mn and Zn were observed, mainly in A. germinans and R. mangle in the port area. In addition, oxidative stress biomarkers were evaluated, such as hydrogen peroxide, reduced glutathione, metallothionein, lipid peroxidation and protein carbonylation. High concentrations of metallothionein, reduced glutathione and hydrogen peroxide were observed in the three species in the port area, indicating a response to oxidative stress, possibly due to adverse environmental conditions and metal contamination. Anatomical analysis identified changes in L. racemosa and R. mangle, such as an increase in the leaf blade, upper and lower epidermis, and palisade and lacunar parenchyma in the dry mangrove area. For all three species, an increase in cuticle thickness and stomatal density was observed in the leaves collected in the potuary area, thus indicating that these anatomical changes may represent adaptations to contaminated environments. Investigations of this type are essential for understanding the adaptive processes of mangrove plants in polluted areas and their capacity to provide ecosystem services, contributing to the preservation and recovery of these highly valuable ecosystems. |
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