Influence of nitrogen and sulfur fertilization on glucosinolate content and composition of horseradish plants harvested at different developmental stages

Horseradish (Armoracia rusticana) is a rich source of glucosinolates (GLS), a class of secondary metabolites, nitrogen and sulfur compounds found in Brassicaceae family. Variations of content and composition of nine GLS in horseradish plants grown with N alone and N plus S were evaluated in the above- and below-ground portions at different developmental stages. Total GLS concentration was significantly higher in the above-ground tissues compared to the roots (97.8 vs 11.6 lmol g-1 dw); it responded positively to N and S supply in roots (11.5 in N alone and 15.8 lmol g-1 dw in N plus S treatments with respect to 7.4 lmol g-1 dw of the untreated control) without significant variations in the above-ground tissues. In both portions, total GLS concentration showed the greatest values at the beginning of plant regrowth and then decreased throughout the plant development till the end of the growing period. Among classes, the aliphatic GLS were the most abundant accounting for over 73 and 97 % of the total GLS in roots and above-ground tissues, respectively. Whereas, aromatic and indole GLS were present at roughly equivalent levels in both portions. GLS classes varied differently depending on developmental stage and fertilization, showing the highest percentage increase at the beginning of plant regrowth: aliphatic GLS increased by 150 % with N alone and 400 % with N and S supply, while aromatics and indoles increased both up to 35 % with N alone and 280 and 180 % with N and S, respectively. The results suggest that fertilization led to modulate GLS content and composition in plants in relation to a specific employment.