Phitotoxicity of Mikania laevigata Schultz Bip. ex Baker extracts or coumarin on Lactuca sativa L., Bidens pilosa L. and Arabidopsis thaliana (L.) Heynh

Abstract

The indiscriminate use of synthetic herbicides to combat invasive plants in cultivated areas is responsible for the contamination of the environment, including humans. Plant extracts are rich in secondary metabolites (allelopathins) that can act as effective herbicides with lower environmental risks. The objective of this work was to evaluate the toxicity of the aqueous and ethanolic extracts from the leaves of M. laevigata on the species Lactuca sativa and Bidens pilosa, through parameters such as germination, initial growth and induction of oxidative stress in vitro (BOD) and in greenhouse. As well as evaluating the physiological, biochemical and morphological changes induced by coumarin isolated [1,2-benzopyrone] on Lactuca sativa and Arabidopsis thaliana. The total germination in percentage [G (%)], IVG (germination speed index) and initial growth were verified. Regarding the biochemical parameters, the levels of hydrogen peroxide (H 2O2 ) and lipid peroxidation (MDA) of L. sativa and B. pilosa were evaluated for antioxidant enzymes (SOD, CAT, APX). Based on the results of the bioassays, it was observed that the ethanolic extract at the 3 mg mL-¹ concentration of M. laevigata, tested in BOD induced oxidative stress causing necrosis. In the greenhouse, using the pre-imbibition method, the ethanolic extract at concentrations 2.0 and 3.0 mg mL -¹ reduced the germination in B. pilosa and L. sativa, and stimulated the production of hydrogen peroxide , followed by increased activity of antioxidant enzymes (SOD, CAT and APX), which were able to reverse the harmful effects of reactive oxygen species on L. sativa. B. pilosa showed to be more sensitive to the extract with higher MDA production. 1,2-Benzopyrone negatively affected L. sativa root germination and growth; the IC 50 (53 μM) increased free proline content (44 %) and IC 80 (85 μM) reduced the concentration of total soluble proteins (22 %). As for root morphology, Arabidopsis thaliana submitted to IC 50 for 14 days showed increased lateral root formation and number of root hairs, ectopic root formation, asymmetric cells and nuclei. The study allowed to increase the knowledge about the physiological and biochemical modes of action of M. laevigata extracts on a horticultural plant (L. sativa) and an invasive plant (B. pilosa) in both in vitro and in a greenhouse assays. As well as the 1,2-benzopyrone coumaries on two test plants L. sativa and A. thaliana. It is hoped that the research may provide subsidies for the proposition of new studies on plant extracts and isolated molecules, in order to search for bioherbicides less toxic to the environment.