Dose-Response—A Challenge for Allelopathy?

Abstract

The response of an organism to a chemical depends, among other things, on the dose. Nonlinear dose-response relationships occur across a broad range of research fields, and are a well established tool to describe the basic mechanisms of phytotoxicity. The responses of plants to allelochemicals as biosynthesized phytotoxins, relate as well to nonlinearity and, thus, allelopathic effects can be adequately quantified by nonlinear mathematical modeling. The current paper applies the concept of nonlinearity to assorted aspects of allelopathy within several bioassays and reveals their analysis by nonlinear regression models. Procedures for a valid comparison of effective doses between different allelopathic interactions are presented for both, inhibitory and stimulatory effects. The dose-response applications measure and compare the responses produced by pure allelochemicals [scopoletin (7-hydroxy-6-methoxy-2H-1-benzopyran-2-one); DIBOA (2,4-dihydroxy-2H-1,4-benzoxaxin-3(4H)-one); BOA (benzoxazolin-2(3H)-one); MBOA (6-methoxy-benzoxazolin-2(3H)-one)], involved in allelopathy of grain crops, to demonstrate how some general principles of dose responses also relate to allelopathy. Hereupon, dose-response applications with living donor plants demonstrate the validity of these principles for density-dependent phytotoxicity of allelochemicals produced and released by living plants (Avena sativa L., Secale cereale L., Triticum L. spp.), and reveal the use of such experiments for initial considerations about basic principles of allelopathy. Results confirm that nonlinearity applies to allelopathy, and the study of allelopathic effects in dose-response experiments allows for new and challenging insights into allelopathic interactions.

Regulation of Cell Division and Growth in Roots of Lactuca sativa L. Seedlings by the Ent-Kaurene Diterpenoid Rabdosin B

“…Examples of hormesis (the stimulation effect of a toxin at low doses) with natural phytotoxins have been reported with single compounds (e.g., gramine and hordenine, benzoxazolin-2(3H)-one, and allyl isothiocyanate), plant extracts (e.g., Triticum aestivum L.), and root exudates (e.g., T. aestivum and Triticum spelta L.) (An et al 1993;Belz et al 2005Belz et al , 2007. Belz (2008) reported that hormetic effects might occur in a natural setting if doses released are low, and they should be regarded as a potential low dose component of plant/plant interference.…”

Allelochemicals as Bioherbicides — Present and Perspectives

“…Therefore, this feature excludes the application of an allelopathic compound as a selective herbicide or totally prohibits its usage in weed management. On the other hand, effects of allelopathins in acceptor plants are highly dose-dependent [13]. This allows the opportunity to search out compounds exhibiting selectivity.…”

Proving Allelopathy in Crop–Weed Interactions

“…All of this is predicated in the assumption that chemical signals and/or competition from the receiving plant species do not influence allelochemical production of the donor species (see discussion above). The results of this type of experiment can also be complicated by hormesis (stimulatory effect of a subtoxic dose of a toxin) effects at low densities of the donor species (Belz et al 2005). Sampling time can also influence the results, so, ideally, several sampling times should be designed into the experiment.…”

“…Some allelochemicals, such as sorgoleone (Dayan et al 2010;Weston et al 2013), m-tyrosine (Bertin et al 2007), and scopoletin (Belz et al 2005) are exuded by roots, and, as in the case of sorgoleone, may be exuded or secreted into the soil almost as quickly as they are produced. Furthermore, soil microbes can convert less-phytotoxic root exudates to more phytotoxic compounds, making the discovery of the true ''allelochemical'' even more difficult.…”

“…Aplotaxene was added to the soil in acetone, allowed to dry and mixed in, and then seeds and water were added. activity value in soil will vary with soil type due to differences in the EC 50 values in different soils (Belz et al 2005;Hiradate et al 2010).…”