2017 ASHS Annual Conference

Exogenous application of methyl jasmonate (MeJA) on Brassica crops has shown to increase indole glucosinolates (GS) while the concentration of aliphatic GS remained unaffected. MeJA application also increased the concentration of myrosinase-mediated hydrolysis products from indole and aliphatic GS that have been shown to have potential health-promoting effect. The presence of MeJA in this practice is similar with the insect herbivory damage however the latter one is relatively gradual and complicated since plants are challenged by the not only physical wounding but also foreign biochemicals including peptides from saliva. To compare the potential differences between two scenarios, control, insect damage (4 days treatment of cabbage looper caterpillars), and MeJA treatment (harvested 4 days after 250 µM MeJA treatment) using Brassica napus var. pabularia ‘Red Russian’ kale for primary metabolites change via gas chromatography mass spectrometer, GS profile, myrosinase activity, and GS hydrolysis products profile were measured. Sugars including fructose, galactose, and raffinose were less accumulated in two treatment groups while certain phenolic acids including ferulic acid and 3-caffeoylquinic acid showed two fold or higher accumulation in insect damaged samples compared to control. Decreased sugar level suggests that they might be a carbon source for secondary metabolite biosynthesis in MeJA-treated and insect damaged kales. Indole GS glucobrassicin, neoglucobrassicin, and 4-methoxyglucobrassicin increased 5.4, 5.6, and 3-fold in insect damaged samples but only increased 3.2, 2.1 and 5.4-fold in MeJA treatment samples. Insect damages samples also showed significantly lower accumulation in two aliphatic GS glucoraphanin (32%) and gluconapin (53%) while MeJA treatment samples were not different from the control. All indole GS hydrolysis products N-methoxyindole-3-carbinol, 1-methoxyindole-3-carboxyaldehyde, and indole-3-acetonitrile were only detected in two treatments groups while the concentration variation within insect damaged sample was larger than MeJA treatment sample. Most of hydrolysis products from aliphatic GS were not statistically difference except the 2-propenythioacetonitrile was significantly lower in insect damaged sample. Myrosinase activity was significant lower in insect damaged samples and was 45% reduction compared to the control. The result demonstrated that the metabolic changes triggered by MeJA application and insect herbivory share similar trend but with quantitative difference and it can provide valuable aspect in agriculture practice with aspect to the health-promoting effect of GS hydrolysis products and the pest control.