Characterization of allelochemicals from Pistia stratiotes extracts and their effects on the growth and physiology of Microcystis aeruginosa.

Due to the public and environmental health impact of cyanotoxins, investigations have been focused on finding environmental friendly algaecides from aquatic plants. The present study had the objective to evaluate the population control and physiological response of Microcystis aeruginosa (Kützing) Kützing (strain BCCUSP232) exposed to Pistia stratiotes L. extracts. Aqueous and ethanolic extracts of P. stratiotes at different concentrations (10, 25, and 50 mg L-1) were submitted to M. aeruginosa and reduced significantly (p<0.05) the cyanobacterium cell density. The ethanolic extract presented the greatest growth inhibition of the strain at the highest concentration. During exposure to P. stratiotes extracts, intracellular hydrogen peroxide levels, malondialdehyde content, and antioxidant enzymes (peroxidase, catalase, and glutathione S-transferase) activities increased in M. aeruginosa, while total protein concentration decreased when compared to the control group. Superoxide dismutase (SOD) activities presented a sharp decline, suggesting superoxide radical and peroxide accumulation. This implied that SOD was a target for bioactive substance(s) from aqueous and ethanolic extracts of P. stratiotes. Phytochemical screening of the extracts revealed that the ethanolic extract presented 93.36 mg gallic acid equivalent (GAE) per gram dry weight (g-1 DW) total polyphenols and 217.33 mg rutin equivalent (RE) per gram dry weight total flavonoids, and for the aqueous extract, 5.19 mg GAE g-1 DW total polyphenols and 11.02 mg RE g-1 DW total flavonoids were detected. Gas chromatography (GC)/mass spectrometry (MS) analyses of the ethanolic and aqueous extracts presented palmitic acid ethyl ester as major allelochemical. In view of these results, it can be concluded that P. stratiotes showed potential in controlling M. aeruginosa populations.

Phytotoxicity of ethanolic extract of turnip leaves (Raphanus sativus L. ) / Fitotoxicidade do extrato etanólico de folhas de nabo (Raphanus sativus L. )

The study of allelopathic activity has been aim of research that evaluates mainly species used in green fertilization. Raphanus sativus L. stands out among these species, because it shows high capacity for nutrient recycling, specially nitrogen and phosphorus, what makes it an advantageous cover plant in crop rotation systems. Considering the exposed, the present study had as objective the evaluation of the allelopathic and phytotoxic potentials of different concentrations of the R. sativus leaves ethanolic extract by mean of seeds germination analyses and development of lettuce seedlings, evaluating the phytotoxicity by determination of the mitotic index of lettuce root cells, realizing the phytochemical profile and investigating the antioxidant activity. It was possible to verify that the R. sativus extract interferes in the germination index, decreasing the germinability (5 mg.mL-1 = 9.84%; 10 mg.mL-1 = 11.91% and 20 mg.mL-1= 57.51%). In the lettuce seedlings growth, the extract of this species affected the roots and hypocotyls growth. It was possible to observe phenols and total flavonoids in the extract for the concentration of 1000µg.mL-1(161mg and 83.57 mg, respectively). It was also observed, higher antioxidant activity for the concentration of 1000 µg.mL-1 (89.76%). In the phytotoxicity assay was observed a dose dependent effect in the mitotic index and in the cellular events during cellular division. In this study it was possible to conclude that this species has allelochemical compounds which are able to interfere directly on the stabilization and development of other species.

O estudo da atividade alelopática tem sido alvo de investigação, avaliando principalmente espécies usadas na adubação verde. Raphanus sativus L. destaca-se entre as espécies, porque mostra alta capacidade de reciclagem de nutrientes, nitrogênio e fósforo, especialmente, o que faz com que seja uma planta de cobertura vantajosa em sistemas de rotação de culturas. Considerando o exposto, o presente estudo teve como objetivo a avaliação dos potenciais alelopáticos e fitotóxico de diferentes concentrações do extrato etanólico de folhas de R. sativus por meio de análises de germinação de sementes e desenvolvimento de mudas de alface, avaliar a fitotoxicidade por determinação do índice mitótico de células da raiz de alface, investigar o perfil fitoquímico e a atividade antioxidante. Foi possível verificar que o extrato de R. sativus interfere no índice de germinação, diminuindo a capacidade de germinação (5 mg.mL-1 = 9,84%; 10 mg.mL-1 = 11,91% e 20 mg.mL-1= 57,51%). No crescimento de mudas de alface o extrato desta espécie afetou o crescimento de raízes e hipocótilos. Foi possível observar uma considerável quantidade de fenóis e flavonóides totais no extrato para a concentração de 1000 µg.mL-1 (161 mg e 83.57 mg, respectivamente). Observou-se, também, a atividade antioxidante mais elevada para a concentração de 10000 µg.mL-1 (89,76%). No ensaio de fitotoxicidade foi observado um efeito dose dependente no índice mitótico e nos eventos celulares durante a divisão celular. Neste estudo foi possível concluir que esta espécie tem compostos aleloquímicos capazes de interferir diretamente na estabilização e desenvolvimento de outras espécies.