Abstract
Plants within the Brassicales order generate glucosinolate hydrolysis products that can exert different biological effects on several organisms. Here, we evaluated the physiological effects of one of these compounds, benzyl cyanide (phenylacetonitrile), when exogenously applied on Arabidopsis thaliana. Treatment with benzyl cyanide led to a dose-dependent reduction of primary root length and total biomass. Further morphological changes like elongated hypocotyls, epinastic cotyledons, and increased formation of adventitious roots resembled a severe auxin-overproducer phenotype. The elevated auxin response was confirmed by histochemical staining and gene expression analysis of auxin-responsive genes. Nitriles are converted by specific enzymes, nitrilases (NIT1-3), to their corresponding carboxylic acids. The nitrilase mutants nit1 and nit2 tolerated benzyl cyanide treatments better than the wild type, with nit2 being less resistant than nit1. A NIT2RNAi line suppressing several nitrilases was resistant to all tested benzyl cyanide concentrations. When exposed to phenylacetic acid (PAA) – the corresponding carboxylic acid of benzyl cyanide – wild type and mutant seedlings were, however, equally susceptible and showed a more severe auxin phenotype than upon cyanide treatment. Here, we demonstrate that the auxin-like effects triggered by benzyl cyanide on Arabidopsis are due to its nitrilase-mediated conversion to the natural auxin PAA.
Highlights
Glucosinolates (GSLs) are nitrogen- and sulfur-containing secondary metabolites of plants belonging to the Brassicales order
Growing Arabidopsis Col-0 on solid in vitro medium supplemented with benzyl cyanide (Bz-CN) at concentrations ranging from 25 to 100 μM for 10 days led to a dose-dependent decrease in primary root length (Figure 1A) and total biomass (Figure 1B)
In addition to a shortening of the primary root and longer hypocotyl, seedlings grown on Bz-CN presented epinastic cotyledons, had longer root hairs and developed numerous adventitious roots (Figure 2 and Supplementary Figure S1)
Summary
Glucosinolates (GSLs) are nitrogen- and sulfur-containing secondary metabolites of plants belonging to the Brassicales order. The hydrolysis of benzylglucosinolate can lead to benzyl-ITC, benzyl thiocyanate, or phenylacetonitrile ( called benzyl cyanide; Virtanen, 1965; Cole, 1976; Gil and Macleod, 1980a,b). Which of these products are formed depends on the plant species, the organ and the developmental stage of the plant, the presence of nitrile-specifier proteins (NSPs) or thiocyanate-forming protein (TFP), as well as cofactors and the reaction conditions (e.g., pH, iron ions; Burow et al, 2007; Wittstock and Burow, 2010; Kuchernig et al, 2012)
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