The Occurrence of Hormesis in Plants and Algae

Abstract

This paper evaluated the frequency, magnitude and dose/concentration range of hormesis in four species: The aquatic plant Lemna minor, the micro-alga Pseudokirchneriella subcapitata and the two terrestrial plants Tripleurospermum inodorum and Stellaria media exposed to nine herbicides and one fungicide and binary mixtures thereof. In total 687 dose-response curves were included in the database. The study showed that both the frequency and the magnitude of the hormetic response depended on the endpoint being measured. Dry weight at harvest showed a higher frequency and a larger hormetic response compared to relative growth rates. Evaluating hormesis for relative growth rates for all species showed that 25% to 76% of the curves for each species had treatments above 105% of the control. Fitting the data with a dose-response model including a parameter for hormesis showed that the average growth increase ranged from 9+/-1% to 16+/-16% of the control growth rate, while if measured on a dry weight basis the response increase was 38+/-13% and 43+/-23% for the two terrestrial species. Hormesis was found in >70% of the curves with the herbicides glyphosate and metsulfuron-methyl, and in >50% of the curves for acifluorfen and terbuthylazine. The concentration ranges of the hormetic part of the dose-response curves corresponded well with literature values.

Physiological Dose-Response of Coffee (Coffea arabica L.) Plants to Glyphosate Depends on Growth Stage

“…Effects of glyphosate on sensible plants are well understood, but, depending on herbicide dose, not only deleterious effects can be caused by exposing plants to the chemical. Many researchers have reported stimulatory effects of low glyphosate doses on growth of different plant species (Cedergreen et al, 2007;Velini et al, 2008;Cedergreen and Olesen, 2010), termed as hormesis.…”

Low Doses of Fenoxaprop-P-Ethyl Cause Hormesis in Littleseed Canarygrass and Wild Oat

“…Growth stimulation due to low doses of different herbicides has been shown in several crop species both in controlled and in the field conditions (Davies et al, 2003;Duke et al, 2006;Cedergreen et al, 2007;Velini et al, 2008). The literature revealed that herbicides at low doses cause on average 20-30% of growth stimulation under controlled conditions (Cedergreen et al, 2007) and 10-25% under uncontrolled field conditions (Cedergreen et al, 2005(Cedergreen et al, , 2009). However, depending on the crop species, type of herbicide and other factors, this average stimulation increased up to 200% (Calabrese, 2008;Velini et al, 2008).…”

“…Research addressing these issues is currently absent and the effects of herbicide hormesis on weed growth and weed crop competition are absent. Most of the published research is about the hormetic responses of crops against herbicides (Davies et al, 2003;Duke et al, 2006;Cedergreen et al, 2007;Velini et al, 2010;Belz et al, 2011). However, for practical implementation of herbicide hormesis to improve crop growth and yield, the effects of these lower doses on weed growth should also be considered.…”

Resposta fisiológica de espécies de eucalipto cultivadas em solo tratado com herbicidas mimetizadores de auxinas

“…The response at 15 and 40 DAP of C. citriodora may be related to this situation, since the photosynthetic result of the species was positively influenced in smaller doses and negatively in larger ones (Figure 2A, B). The auxin-mimetic can act as growth stimulants in plants, specially when they are found in low levels in the soil (Cedergreen et al, 2007;Calabrese & Blain, 2009). …”

“…Some herbicides used in sub-doses may exert an inverse function and assist in plant development (Cedergreen et al, 2007;Silva et al, 2009). In larger doses, there was a stimulatory effect of the auxin herbicide.…”