Toxicity of hydrolysis volatile products of 'Brassica' plants to 'Sclerotinia sclerotiorum', in vitro
Oilseed rape stem rot disease caused by 'Sclerotinia sclerotiorum' causes serious yield losses worldwide. Glucosinolates as specific secondary metabolites of 'Brassicaceae' are produced in various parts of the host plants. Their enzymatic hydrolysis releases chemical components, particularly isothiocyanates, with fungitoxic activity and volatile characteristics. To investigate the effect of volatiles derived from 'Brassica' tissues, the pathogen was exposed to hydrolysis products of 'Brassica' shoot parts as sources of glucosinolates including oilseed rape varieties and two species, black and white mustard. The results showed significant differences in inhibition of 'S. sclerotiorum' growth between varieties and species. All tissues of black mustard inhibited completely the exposed colonies of the pathogen and oilseed rape varieties Dunkeld, Oscar and Rainbow had significant inhibitory effect on the fungus. The genotypes demonstrated significant differences for the production of toxic volatiles, indicating that GSL contents in Brassica species and even cultivars have different potentials for toxic products.
Tryptophan-Independent Indole-3-Acetic Acid Synthesis: Critical Evaluation of the Evidence
Trp-independent synthesis of indole-3-acetic acid (IAA) was proposed back in the early 1990s based on observations from Trp auxotrophs inmaize (Zeamays; Wright et al., 1991) and Arabidopsis (Arabidopsis thaliana; Normanly et al., 1993). Recently, Wang et al. (2015) published new data suggesting that a cytosolic indole synthase (INS) may catalyze the first step separating the Trp-dependent and Trp-independent pathways in Arabidopsis. If this is the case, it would be a major breakthrough; however, in this article, I critically evaluate both recent and older evidence for the Trp-independent route and suggest that the INS is more likely to participate in Trp-dependent IAA production.