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Evaluation of phytotoxicity of seaweed extracts from the Portuguese coast on tomato plants
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Abstract(s)
Prevê-se que a população mundial mantenha um crescimento constante nos próximos anos, pelo que a gestão correcta da agricultura é imperativa para responder adequadamente à crescente procura de alimentos. Esta procura elevada levou à intensificação das actividades agrícolas, incluindo a implementação de produtos fitofarmacêuticos destinados a proteger os cultivos de organismos nocivos, pragas e doenças. Mas a utilização destas estratégias químicas apresenta efeitos nocivos para o ambiente e para a saúde humana. Neste contexto, o ambiente marinho representa uma fonte ampla e valiosa de novos compostos interessantes para substituir os atualmente utilizados. Embora os compostos de origem natural sejam considerados seguros para o consumo humano, o estudo do impacto real da sua aplicação continua a ser indispensável.
Assim, o objetivo desta dissertação foi avaliar o potencial antioxidante de vinte e quatro extractos diferentes produzidos a partir das algas marinhas Asparagopsis armata, Codium sp., Fucus vesiculosus e Sargassum muticum, bem como a fitotoxicidade dos extractos aquoso e hidroetanólico.
A preparação dos extractos foi realizada através de uma extração sólido-líquido com água, etanol e água (75:25), apenas etanol, acetato de etilo e n-hexano como solventes. No que diz respeito às actividades biológicas, a atividade antioxidante dos compostos foi avaliada através dos métodos 2,2-difenil-1-picrilhidrazil (DPPH), capacidade de absorção do radical oxigénio (ORAC) e poder antioxidante redutor férrico (FRAP), bem como o conteúdo fenólico total (TPC). O efeito fitotóxico foi avaliado, em primeiro lugar, por um ensaio in vitro de punção das folhas, no qual folhas destacadas de tomateiro (Solanum lycopersicum; Solanaceae) foram aplicadas extractos previamente preparados em três concentrações diferentes (0,1; 0,5; e 1,0 mg/mL). Posteriormente, uma segunda abordagem foi avaliada em um ensaio in vivo em estufa, onde extratos aquosos liofilizados e hidroetanólicos foram aplicados em plantas de tomate por pulverização, semanalmente, durante 42 dias.
A análise dos extractos revelou valores baixos de conteúdo fenólico total. Os extractos hidroetanólico e etanólico de F. vesiculosus apresentaram os valores mais
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elevados. No contexto da atividade de redução do radical DPPH, F. vesiculosus (hidroetanólico, etanólico e acetato de etilo), A. armata (acetato de etilo) e S. muticum (etanólico) apresentaram os resultados mais promissores, reduzindo mais de 50% do radical DPPH. Relativamente ao método FRAP, os resultados foram significativamente inferiores aos do BHT. Por outro lado, o resultado obtido no método ORAC foi significativamente superior ao do BHT, mas ainda muito baixo em comparação com outros compostos antioxidantes, como o ácido ascórbico. Em relação ao ensaio de punção foliar, os extractos não apresentaram diferenças significativas quando comparados com os controlos avaliados. Por outro lado, as plantas em estudo in vivo após 42 dias de tratamento não mostraram nem fitotoxicidade nem efeito bioestimulante.
Em conclusão, foram obtidos diferentes extractos de quatro algas marinhas diferentes e, globalmente, mostraram uma fraca capacidade antioxidante. Não se verificou qualquer efeito de fitotoxicidade nas plantas, no entanto, a temperatura elevada durante o período experimental na estufa foi um fator que afectou negativamente o crescimento das plantas de tomate. Embora nas condições apresentadas não tenha havido efeito positivo nas plantas, o facto de não ter apresentado efeito negativo e fitotoxicidade é favorável ao desenvolvimento de produtos com outras acções, como os biopesticidas.
The global population is projected to maintain a steady growth the coming years, thus the correct management of agriculture is imperative to adequately address the escalating demand of food. This elevated demand has lead to the intensification of agriculture activities, including the implementation of plant protection products aiming to protect orchards from harmful organisms, pest, and diseases. But the use of these chemic strategies present harmful effects over the environment and human health. Within this context, marine environment represents a wild and valuable source of interesting new compounds to replace the current used. Even though natural origin compounds are considered safe for human consumption, the study of the real impact of its application remains indispensable. Therefore, the objective of this dissertation was assessing the antioxidant potential of twenty-four different extracts produced from the seaweeds Asparagopsis armata, Codium sp., Fucus vesiculosus and Sargassum muticum, as well as the phytotoxicity of aqueous and hydroethanolic extracts. The preparation of extracts was achieved through a solid-liquid extraction with water, ethanol and water (75:25), only ethanol, ethyl acetate and n-hexane as solvents. Regarding biological activities, antioxidant activity of compounds was evaluated through the 2,2-diphenyl-1- picrylhydrazyl (DPPH), oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP) methods, as well as total phenolic content (TPC). The phytotoxicity effect was assessed firstly by an in vitro leaf puncture assay, which detached tomato (Solanum lycopersicum; Solanaceae) leaves were submitted to extracts previously prepared at three different concentrations (0.1; 0.5; and 1.0 mg/mL). Subsequently, a second approach was evaluated in an in vivo assay in a greenhouse, where aqueous lyophilized and hydroethanolic extracts were applied in tomato plants by spraying, weekly for 42 days. The analysis of the extracts revealed low values of total phenolic content. F. vesiculosus hydroethanolic and ethanolic extracts exhibiting the highest values. In the context of DPPH radical scavenging activity, F. vesiculosus (hydroethanolic, ethanolic and ethyl acetate), A. armata (ethyl acetate) and S. muticum (ethanolic) displayed the most promising results, reducing more than 50% DPPH radical. Regarding FRAP method, results were significantly lower than BHT. In the other hand, the result obtained in the ORAC method was significantly higher than BHT, but still very low comparing to other antioxidant compounds, as ascorbic acid. Regarding the leaf puncture assay, extracts did not show significant differences when compared with controls assessed. On the other hand, the in vivo study plants after 42 days of treatment did not show nether a phytotoxicity or a bio stimulant effect. In conclusion, different extracts were obtained from four different seaweeds and, globally, showed poor antioxidant capacity. No phytotoxicity effect was found on the plants, however, the high temperature during the experimental period in the greenhouse was a factor that negatively affected tomato plants growth. Although under the conditions presented there was no positive effect on the plants, the fact that it did not present a negative effect and phytotoxicity is favorable to the development of products with other actions, such as biopesticides.
The global population is projected to maintain a steady growth the coming years, thus the correct management of agriculture is imperative to adequately address the escalating demand of food. This elevated demand has lead to the intensification of agriculture activities, including the implementation of plant protection products aiming to protect orchards from harmful organisms, pest, and diseases. But the use of these chemic strategies present harmful effects over the environment and human health. Within this context, marine environment represents a wild and valuable source of interesting new compounds to replace the current used. Even though natural origin compounds are considered safe for human consumption, the study of the real impact of its application remains indispensable. Therefore, the objective of this dissertation was assessing the antioxidant potential of twenty-four different extracts produced from the seaweeds Asparagopsis armata, Codium sp., Fucus vesiculosus and Sargassum muticum, as well as the phytotoxicity of aqueous and hydroethanolic extracts. The preparation of extracts was achieved through a solid-liquid extraction with water, ethanol and water (75:25), only ethanol, ethyl acetate and n-hexane as solvents. Regarding biological activities, antioxidant activity of compounds was evaluated through the 2,2-diphenyl-1- picrylhydrazyl (DPPH), oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP) methods, as well as total phenolic content (TPC). The phytotoxicity effect was assessed firstly by an in vitro leaf puncture assay, which detached tomato (Solanum lycopersicum; Solanaceae) leaves were submitted to extracts previously prepared at three different concentrations (0.1; 0.5; and 1.0 mg/mL). Subsequently, a second approach was evaluated in an in vivo assay in a greenhouse, where aqueous lyophilized and hydroethanolic extracts were applied in tomato plants by spraying, weekly for 42 days. The analysis of the extracts revealed low values of total phenolic content. F. vesiculosus hydroethanolic and ethanolic extracts exhibiting the highest values. In the context of DPPH radical scavenging activity, F. vesiculosus (hydroethanolic, ethanolic and ethyl acetate), A. armata (ethyl acetate) and S. muticum (ethanolic) displayed the most promising results, reducing more than 50% DPPH radical. Regarding FRAP method, results were significantly lower than BHT. In the other hand, the result obtained in the ORAC method was significantly higher than BHT, but still very low comparing to other antioxidant compounds, as ascorbic acid. Regarding the leaf puncture assay, extracts did not show significant differences when compared with controls assessed. On the other hand, the in vivo study plants after 42 days of treatment did not show nether a phytotoxicity or a bio stimulant effect. In conclusion, different extracts were obtained from four different seaweeds and, globally, showed poor antioxidant capacity. No phytotoxicity effect was found on the plants, however, the high temperature during the experimental period in the greenhouse was a factor that negatively affected tomato plants growth. Although under the conditions presented there was no positive effect on the plants, the fact that it did not present a negative effect and phytotoxicity is favorable to the development of products with other actions, such as biopesticides.
Description
Funding: This project was funded by ORCHESTRA—add-value to ORCHards through thE full valoriSaTion of macRoalgAe (POCI-01-0247-FEDER-070155) cofounded by FEDER—Fundo Europeu de Desenvolvimento Regional da UniãoEuropeia, Portugal2020, through COMPETE 2020—Programa Operacional Competitividade e Internacionalização and through undação para a Ciência e a Tecnologia (FCT). This project was also funded by COSMOS: Valorização biotecnológica da alga invasora Asparagopsis armata da Costa de Peniche (MAR-04.03.01-FEAMP-0370) through GAL PESCA OESTE and MAR2020 in the framework of PORTUGAL2020 and the European Maritime and Fisheries Fund and OCEANFIRE funded by Fundação Amélia de Mello through the Alfredo da Silva award.
Keywords
Agricultura Macroalgas Atividade antioxidante Compostos bioativos Ensaio de punção de folha Fitotoxicidade, Recursos marinhos Agriculture Macroalgae Antioxidant activity Bioactive compounds Leaf puncture assay Marine resources, Phytotoxicity