Modelos vegetais aplicados a estudos de toxicologia ambiental: uma abordagem comparativa entre Allium cepa L. e Lactuca sativa L.

Abstract

In view of the environmental pollution issue, the importance of raising all information on the chemical composition and the effect of pollutants on living organisms has been recognized. Among the bioassays available for this purpose, those using plants as biological models can be highlighted, owing to their low costs and ease of performance. Allium cepa L. (onion) is the plant model most broadly used in cytogenotoxic studiesworldwide, while Lactuca sativa (lettuce) is especially employed in phytotoxic studies. Because onion and lettuce are models well known among researchers around the world, and given that no approaches exist so far comparing their efficiency in bioassays to assess the risk of environmental pollutants, the present study aimed to compare (1) the early onion and lettuce seedling development and mitotic index without presence of chemical compounds, (2) the chromosome set of these two model species, and (3) the responses of both species in assays of seedling growth, chromosome and nuclear alterations, cell death and DNA fragmentation after exposure of the roots to different environmental pollutants.Inthe first approach (1), it was observed that lettuce has fast and standardized germination, rapid initial seedling development and high MI in comparison to onion, standing out in studies of environmental toxicology due to enabling simple, rapid and efficient analysis of these parameters. Further, revisiting the karyotypes of both model species (2) revealed length of onion chromosomes ranging from 7.13 to 10.54 µm when treated with colchicine and from 6.26 to 9.18 µm when treated with 8HQ, whereas the length of lettuce chromosomes varied from 3.21 to 6.04 µm with colchicine and 1.85 to 3.33 µm with 8HQ, attesting the importance of such data for research groups investigating the toxic effects of environmental pollutants. In the third experiment (3), onion and lettuce roots were exposed to the DNA-alkylating agent MMS and to environmental pollutants (Cadmium, SPL and Atrazine) for analysis of root growth, cell cycle and DNA fragmentation via TUNEL and comet assays. Both species showed sensitive and efficient response to the tests. Overall, the onion model was more efficient in detecting clastogenic changes, arising from DNA breakage, while the lettuce model rather detected aneugenicalterations, related to chromosome segregation in mitosis. In the DNA fragmentation analysis, onion showed higher sensitivity in the comet assay and in the TUNEL test. In conclusion, both plants are efficient to evaluate toxicological risks of environmental pollutants.