Date Published: January 17, 2019
Publisher: Public Library of Science
Author(s): Livia Deice Raasch-Fernandes, Solange Maria Bonaldo, Domingos de Jesus Rodrigues, Gerardo Magela Vieira-Junior, Kátia Regina Freitas Schwan-Estrada, Camila Rocco da Silva, Ana Gabriela Araújo Verçosa, Daiane Lopes de Oliveira, Bryan Wender Debiasi, Stefan Lötters.
Cutaneous secretions produced by amphibians of the family Bufonidae are rich sources of bioactive compounds that can be useful as new chemical templates for agrochemicals. In crop protection, the use of elicitors to induce responses offers the prospect of durable, broad-spectrum disease control using the plant’s own resistance. Therefore, we evaluated the potential of methanolic extracts of cutaneous secretions of two species of amphibians of the family Bufonidae found in the Amazon biome—Rhaebo guttatus (species 1) and Rhinella marina (species 2)—in the synthesis of phytoalexins in soybean cotyledons, bean hypocotyls, and sorghum mesocotyls. Additionally, changes in the enzyme activity of β-1,3-glucanase, peroxidase (POX), and polyphenol oxidase (PPO) and in the total protein content of soybean cotyledons were determined. In the soybean cultivar ‘TMG 132 RR’, our results indicated that the methanolic extract of R. guttatus cutaneous secretions suppressed glyceollin synthesis and β-1,3-glucanase activity and increased POX and PPO activities at higher concentrations and total protein content at a concentration of 0.2 mg/mL. On the other hand, the methanolic extract of R. marina cutaneous secretions induced glyceollin synthesis in the soybean cultivars ‘TMG 132 RR’ and ‘Monsoy 8372 IPRO’ at 0.1–0.2 mg/mL and 0.2 mg/mL, respectively. The methanolic extract of R. marina cutaneous secretions also increased the specific activity of POX and PPO in ‘Monsoy 8372 IPRO’ and ‘TMG 132 RR’, respectively, and decreased the activity of β-1,3-glucanases in ‘Monsoy 8372 IPRO’. At 0.3 mg/mL, it stimulated phaseolin synthesis. The extracts did not express bioactivity in the synthesis of deoxyanthocyanidins in sorghum mesocotyls. The study in soybean suggests that the bioactivity in defense responses is influenced by cultivar genotypes. Therefore, these results provide evidence that extracts of cutaneous secretions of these amphibians species may contribute to the bioactivity of defense metabolites in plants.
Chemical control is a nearly indispensable tool in the management of cultivated plant diseases and pests. The continuous application of non-selective synthetic fungicides and pesticides on food crops has been a growing global concern because of the potential deleterious effects on human health and the environment . Moreover, the indiscriminate and excessive use of fungicides on crops has been a major cause of the development of resistant pathogen populations, resulting in the use of higher concentrations of these antifungals and the consequent increase in toxic residues in food products . To ameliorate this situation, researchers are actively investigating alternative methods of disease and pest control.
Amphibian species the family Bufonidae have recently emerged as powerful tools to provide a rich source of secondary metabolites that can be useful as new chemical templates for drug discovery. In the last decades, many discoveries of novel chemical structures and biological mechanisms that can be applied for the development of disease and pest control agents in agrochemical research have had their origin in a wide range of natural products from a variety of sources. This study established that crude extracts of cutaneous secretions of R. guttatus and R. marina are capable of promoting bioactivity in some defense responses in soybean cultivars and bean. Thus, the methanolic extract of the cutaneous secretions of R. guttatus suppressed glyceollin synthesis and GLU activity in ‘TMG 132 RR’. In ‘TMG 132 RR’, the extract induced POX and PPO activities at higher concentrations. In the same cultivar, higher total protein content was observed at the concentration of 0.2 mg/mL. In ‘Monsoy 8372 IPRO’, the lower concentration of this extract (0.1 mg/mL) increased total protein content. For the extract of the R. marina species, glyceollin synthesis was induced at lower concentrations in ‘Monsoy 8372 IPRO’ and ‘TMG 132 RR’. Minor concentrations of this extract also induced phaseolin synthesis in beans. Regarding enzymatic activity, induction of POX activity was observed at higher concentrations in ‘Monsoy 8372 IPRO’ (0.5 mg/mL). In this same cultivar, PPO and GLU activities were reduced in the presence of this extract. In ‘TMG 132 RR’, higher PPO activity was observed at a lower concentration (0.1 mg/mL). The study in soybean suggests that the bioactivity in defense responses is influenced by cultivar genotypes. In sorghum mesocotyls, the extracts did not express bioactivity.