Impact of nitrogen and sulfur fertilization on the composition of glucosinolates in relation to sulfur assimilation in different plant organs of broccoli.

Broccoli (Brassica oleracea var. italica) is one of the most important winter season vegetables and a rich source of chemoprotective molecules, including glucosinolates (GSL). The aim of this study was to investigate the impact of nitrogen (N) and sulfur (S) fertilization on GSL concentration and composition in different parts of broccoli plants. A greenhouse experiment was performed, with four different treatments of sulfur (10, 30, 70, and 150 kg/ha) and three treatments of nitrogen (50, 250, and 600 kg/ha). GSL concentrations and plant growth responded to the N supply, but this was not observed above the 250 kg N/ha dose. On the contrary, plant growth did not respond to the S supply, whereas GSL concentrations showed a sharp response to the whole range of S applications (from 10 to 150 kg/ha). Glucosinolate composition was altered differentially in the examined plant parts. Aliphatic GSL were more abundant in the florets and leaves, whereas indolyl GSLs were dominant in roots, in which aromatic GSL were also observed. High nitrogen fertilization had a higher impact on indolyl compared to aliphatic GSLs concentration. More importantly, a high concentration of aliphatic GSL, >2.4 micromol/g dry weight (dw), and high S assimilation into aliphatic GSL were consistently observed in the florets compared to other broccoli parts, indicating adaptable processes for nitrogen and sulfur regarding synthesis and transport of aliphatic GSL for these organs.