Zinc availability in hydroponic culture influences glucosinolate concentrations in Brassica rapa

Rapid cycling Brassica rapa L. were grown for 7 days in the presence of 11 levels of zinc (Zn) in hydroponic solution culture and evaluated for changes in Zn and glucosinolate (GS) content. Zinc levels were 0.05, 1, 5, 10, 25, 50, 75, 100, 125, 150, and 200 mg(.)L(-1) Zn. Plants grown in solutions with greater than or equal to50 mg(.)L(-1) Zn displayed severe Zn toxicity symptoms, grew little, or died and were not subsequently evaluated for GS content. Shoot Zn concentrations increased linearly with increasing Zn treatment levels. Gluconapin, which accounted for nearly 90% of the aliphatic GSs present, was the only aliphatic GS influenced by Zn, and decreased linearly with increasing Zn levels. Accumulation of glucobrassicin and 4-metboxyglucosbrassicin, both indole GSs, responded with a linear increase and quadratically, respectively, to Zn fertility. An aromatic GS, gluconasturtiin, was also influenced by Zn levels in solution, and had a quadratic response to increasing Zn. This suggested that Zn fertility can influence changes in GS that may affect flavor (bitterness, etc.) or medicinal attributes associated with the GS and their breakdown products, as well as elevate the nutritional status of Zn in the leaves of Brassica.