Exogenous Methyl Jasmonate Promotes Glucosinolate Accumulation and Antioxidant Capacity in Kale Sprouts

Glucosinolates in two genotypes of kale sprouts treated with methyl jasmonate (MeJA) were analyzed using ultrahigh-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS). This approach enabled the identification of 13 distinct glucosinolates (GSLs) and the quantitative determination of their individual contents. Our results show that MeJA induced GSL biosynthesis, resulting in a significant increase in the total content of aliphatic, indolic, and aromatic GSLs, while also altering their compositional profiles. Notably, the contents of sinigrin (SIN), glucoraphanin (GRA), glucobrassicin (GBC), and glucotropaeolin (GTL) were significantly increased, accompanied by upregulation of key biosynthetic genes, including BoMYB51, BoMYB122, BoSOT18, BoST5a, and BoCYP79A2. MeJA also promoted the accumulation of total phenolics and flavonoids and enhanced CAT and POD activities, associated with improved DPPH radical scavenging activity. However, these metabolic changes were associated with significant growth inhibition, suggesting a trade-off between phytochemical enhancement and biomass production. Genotype-dependent differences were observed between the two lines, with R6 showing stronger anthocyanin induction but weaker GSL responses than W3, indicating that pre-existing metabolic background determines MeJA efficacy. These findings confirm the elicitor effects of MeJA while highlighting the need to balance growth and nutritional quality in potential applications.