Chemical Basis for the Phytotoxicity of Indoles in Relation to the Allelopathy of Cereals

Héctor R Bravo,Sylvia Copaja

doi:10.4236/as.2018.911101

Abstract

Phytotoxic activity of an indole series substituted with electron-acceptor and electron-donor groups in the aromatic ring was determined. They are potential decomposition products, of natural indole alkaloids in cereals plants with allelopathic properties. Phytotoxic selectivity was evaluated from antialgal activity against the microalga Chlorella vulgaris, seed germination seeds and biomass weight of seedling of barley, rye, wheat, oat and maize species and the weed Lolium rigidum. Lipophilia character of the compounds was determined by RP-HPLC method. Both, the electronic character of the substituents, evaluated from σp parameter, and the lipophilia character of the molecules measured from logPHPLC parameter, are involved in the phytotoxic activity. The three bio indicators has shown that the compounds with the higher electron-acceptor groups showed the higher level of phytotoxicity and the molecules with electron-donor groups showed the lowest activity, although, in some cases, this behavior is modified by the lipophilic properties of the molecules. These results are rationalized in terms of polarization of N-H bond of heterocyclic ring. Compounds with the higher logPHPLC values showed the higher phytotoxic activity. Further evidence on the role of lipophilicity was obtained from linear regression between the average inhibitions percentages of biomass and logPHPLC values. The activity increased linearly by increasing the lipophilic character of the compounds. Therefore, quantitative effects in the phytotoxic activity of the electronic properties of the substituents in the aromatic ring and lipophilic character of the indoles can be inferred from σp and logPHPLC parameters, respectively. The results strongly suggest that the potential decomposition products of the natural indole alkaloids from cereals or other natural sources may be in connection with the allelopathic phenomenon of plants when are released into the soil.

Highlights

The use of synthetic herbicides in agriculture can affect the environment negatively; currently it does not represent an effective tool for the control of some weeds developing resistance
To gain deeper understanding of the role in the allelopathy of potential decomposition products from indole alkaloids, in this study we report the phytotoxic profile of a model series of indoles substituted in the aromatic ring (Figure 1)
The results suggest that indole residues substituted in the aromatic ring can be playing a relevant role on the allelopathic phenomenon when are released from the plants

Summary

Introduction

The use of synthetic herbicides in agriculture can affect the environment negatively; currently it does not represent an effective tool for the control of some weeds developing resistance. Research on allelopathic interactions between plants has been focused on agricultural crops as an option in the development of integrated weed management strategies, reducing negative environmental effects and the cost of crop protection [1] [2] [3]. A number of crops exhibit allelopathic interactions that influence the germination, growth, development and yield of other crops, growing either simultaneously or subsequently in agricultural soils. The allelopathy by crops arises when allelochemicals are released from living plants or decomposition residues in the soil. When considering the possible exploration allelochemicals in agriculture it is important to know the phytotoxicity of degradation metabolites

Methods

Results

Conclusion