Comparative effect of elicitors on the physiology and secondary metabolites in broccoli plants

Elicitation is an economic and sustainable technique for increasing the content of secondary metabolites, mainly bioactive compounds, in plants grown for better human nutrition. The aim of this study was to compare the physiological responses (water relations and mineral nutrition) and the enrichment in glucosinolates (GLSs) and phenolic compounds of broccoli plants (Brassica oleracea L. var. italica) receiving different elicitation treatments. The treatments involved the priming of seeds with KCl and the exposure of plants to elicitors, including K₂SO₄ and NaCl solutions and foliar sprays of methyl jasmonate (MeJA), salicylic acid (SA), and methionine (Met). The physiological response of the plants in terms of root hydraulic conductance was improved by priming with KCl and elicitation with MeJA or Met. Foliar application of Met significantly increased the plant biomass and enhanced mineral nutrition. In general, all treatments increased the accumulation of indole GLSs, but K₂SO₄ and MeJA gave the best response and MeJA also favored the formation of a newly described compound, cinnamic-GLS, in the plants. Also, the use of Met and SA as elicitors and the supply of K₂SO₄ increased the abundance of phenolic compounds; K₂SO₄ also enhanced growth but did not alter the water relations or the accumulation of mineral nutrients. Therefore, although the response to elicitation was positive, with an increased content of bioactive compounds, regulation of the water relations and of the mineral status of the broccoli plants was critical to maintain the yield.