title: Nutrient Supply and Simulated Herbivory Differentially Alter the Metabolite Pools and the Efficacy of the Glucosinolate-Based Defense System in Brassica Species.
abstract: Environmental stress hinders growth of plants and commonly results in the accumulation of carbon-based defense compounds. However, the dynamics of nitrogen (N)-containing defense compounds are less predictable under environmental stress. The impact of nutrient deficiency on plant defenses that require the metabolic conversion of a less toxic compound to a more potent toxin is even more poorly understood. We evaluated the effects of nitrogen (N) and potassium (K) deficiency and simulated herbivory on the concentration of metabolites including glucosinolates (GSLs), on the conversion of GSLs to more toxic isothiocyanates (ITCs), and on the activity of myrosinase (MYR) in leaves of Brassica juncea and Brassica nigra. Both species contained GSLs, predominantly sinigrin, but also derivatives of glucobrassicin. Compared to the control, N deficiency increased the sinigrin concentration in both species. Methyl jasmonate (MeJA) application increased sinigrin production in B. junceae, whereas in B. nigra MeJA increased sinigrin only under K-deficiency. Compared to the aliphatic-glucosinolates, MeJA application produced a greater compositional change in the profiles of indolic-glucosinolates. In both species the increase in sinigrin content of the tissue was associated with a decrease in its overall nutritive value as assessed by the content of sugars and amino acids. In B. juncea, application of MeJA decreased the conversion of sinigrin to allyl isothiocyanate (AITC) under both N and K deficiency. The potential activity of MYR decreased in both species under N deficiency. The reduced conversion of sinigrin to AITC and the lower activity of MYR suggest that the GSL-ITC defense system might have a limited efficiency in deterring generalist herbivores under environmental stress.
authors.affiliation: Department of Plant and Environmental Science, Clemson University, 120 BRC, 105 Collins Street, Clemson, SC, 29634, USA.
authors.forename: Makhdora
authors.initials: M
authors.lastname: Almuziny
authors.affiliation: Department of Plant and Environmental Science, Clemson University, 120 BRC, 105 Collins Street, Clemson, SC, 29634, USA.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Decker
authors.affiliation: USDA Agricultural Research Service, Water Management Research Unit, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier, CA, 93648, USA.
authors.forename: Dong
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Mathematical Sciences, Clemson University, Clemson, SC, 29634, USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: Gerard
authors.affiliation: Department of Plant and Environmental Science, Clemson University, 120 BRC, 105 Collins Street, Clemson, SC, 29634, USA. ntharay@clemson.edu.
authors.forename: Nishanth
authors.identifier: http://orcid.org/0000-0001-6866-0804
authors.initials: N
authors.lastname: Tharayil
mesh_terms: D000085:Acetates / Q000494:pharmacology; D003517:Cyclopentanes / Q000494:pharmacology; D005961:Glucosinolates / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000378:metabolism; D060434:Herbivory; D008954:Models, Biological; D009149:Mustard Plant / Q000254:growth & development / Q000378:metabolism* / Q000469:parasitology; D009584:Nitrogen / Q000172:deficiency*; D054883:Oxylipins / Q000494:pharmacology; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: D000085:Acetates; D003517:Cyclopentanes; D005961:Glucosinolates; D054883:Oxylipins; C072239:methyl jasmonate; D006026:Glycoside Hydrolases; C022739:thioglucosidase; D009584:Nitrogen; D011188:Potassium
keywords: Brassica; Glucosinolate; High-resolution-accurate-mass (HRAM); Isothiocyanate; Mass spectrometry; Metabolomics; Methyl jasmonate; Myrosinase; Orbitrap mass analyzer