Sulfur but not nitrogen supply increases the ITC/Nitrile ratio in Pak Choi (Brassica rapa subsp. chinensis (L.) Hanelt)
Glucosinolates (GLS) are a serendipitous class of secondary metabolites found in pak choi, a Chinese cabbage (Brassica rapa subsp. chinensis (L.) Hanelt). GLS are hydrolyzed by the enzyme myrosinase to obtain isothiocyanates (ITC), nitriles, and epithionitriles. GLS hydrolysis products (GLS-HP) are responsible for the typical flavor and odour of pak choi. Little is known about the influence of S and N interactions on pak choi GLS and their hydrolysis products (GLS-HP), especially nitriles.
We investigated the effect of S and N concentrations on pak choi GLS, isothiocyanates, and nitriles content under varying nitrogen (0.75 and 1.5 g N pot–1) and sulfur (0, 0.06, and 0.3 g S pot–1) supply. Increasing the S supply but not N resulted in a reciprocal increase of the total GLS. The GLS concentration decreased under S deficiency. S supply delivered an optimized GLS pattern, and substantially enhanced the synthesis of aliphatic GLS and ITC in particular. In contrast, N-rich nutrition favored the synthesis of indolic GLS and nitriles, the latter are known to have less health beneficial potential and even showed harmful effects. The study indicates, for the first time, that the ITC/nitrile ratio increases under S supply.
GLS and their GLS degradation products in pak choi showed a strong response to sulfur supply. Moreover, the ITC/nitrile ratio might be used as a physiological trait to compare nutritional quality and health benefits of brassica species.
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