Cultivar-Specific Changes in Primary and Secondary Metabolites in Pak Choi (Brassica Rapa, Chinensis Group) by Methyl Jasmonate.

Moo Jung Kim,Kang-Mo Ku,Na Kyung Kim,Hye Min Park,Yu-Chun Chiu,John A Juvik,Choong Hwan Lee

doi:10.3390/ijms18051004

Abstract

Glucosinolates, their hydrolysis products and primary metabolites were analyzed in five pak choi cultivars to determine the effect of methyl jasmonate (MeJA) on metabolite flux from primary metabolites to glucosinolates and their hydrolysis products. Among detected glucosinolates (total 14 glucosinolates; 9 aliphatic, 4 indole and 1 aromatic glucosinolates), indole glucosinolate concentrations (153–229%) and their hydrolysis products increased with MeJA treatment. Changes in the total isothiocyanates by MeJA were associated with epithiospecifier protein activity estimated as nitrile formation. Goitrin, a goitrogenic compound, significantly decreased by MeJA treatment in all cultivars. Changes in glucosinolates, especially aliphatic, significantly differed among cultivars. Primary metabolites including amino acids, organic acids and sugars also changed with MeJA treatment in a cultivar-specific manner. A decreased sugar level suggests that they might be a carbon source for secondary metabolite biosynthesis in MeJA-treated pak choi. The result of the present study suggests that MeJA can be an effective agent to elevate indole glucosinolates and their hydrolysis products and to reduce a goitrogenic compound in pak choi. The total glucosinolate concentration was the highest in “Chinese cabbage” in the control group (32.5 µmol/g DW), but indole glucosinolates increased the greatest in “Asian” when treated with MeJA.

Highlights

Pak choi (Brassica rapa, Chinensis group) is a cool-season crop similar to many other Brassica vegetables, such as kale and broccoli, and was domesticated in China [1]
Other compounds, such as crambene, 1-cyano-3,4-epithiobutane, 1-cyano-4,5-epithiopentane and 1-cyano-2-hydroxy-3,4-epithiobutane, changed with methyl jasmonate (MeJA) treatment depending on cultivar. These results indicate that epithiospecifier protein (ESP) activity in general increased with MeJA in most pak choi cultivars and partially explains why isothiocyanates tended to decrease with MeJA application
The effects of foliar application of MeJA on glucosinolates, their hydrolysis products and primary metabolites were analyzed in five pak choi cultivars

Summary

Introduction

Pak choi (Brassica rapa, Chinensis group) is a cool-season crop similar to many other Brassica vegetables, such as kale and broccoli, and was domesticated in China [1]. As a Brassica vegetable, pak choi provides a number of phytonutrients, in particular glucosinolates (19.36–63.43 μmol/g DW according to Wiesner et al [3]). Pak choi contains a number of glucosinolates including gluconapin, glucobrassicanapin, progoitrin, glucobrassicin and neoglucobrassicin [3,4]. Glucosinolates are nitrogen- and sulfur-containing secondary metabolites derived from amino acids. Depending on their structure and precursor amino acid, glucosinolates are classified into three major groups: aliphatic (from methionine), indole (from tryptophan) and aromatic (from phenylalanine or tyrosine) glucosinolates (Figure 1) [5]. A number of cell culture and pre-clinical studies have reported that Brassica vegetables and glucosinolate hydrolysis products are beneficial against carcinogenesis [8,9,10]. Increasing glucosinolate concentration could be a good strategy to enhance the potential health benefits of Brassica vegetables including pak choi

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