Zinc concentration in hydroponic solution culture influences zinc and sulfur accumulation in Brassica rapa L.

A rapid cycling population of Brassica rapa L. was grown hydroponically and subjected to solution zinc (Zn) concentrations ranging from 0.05 to 200 mg L(-1). The objectives of the study were to determine how available Zn affected plant growth, and the accumulation of Zn, total sulfur (S), sulfate (SO(4)(2-)) in B. rapa shoots. Plants exposed to Zn levels above 5 mg L(-1) exhibited mild visual toxicity symptoms as well as stunted root and shoot growth. Plants exposed to Zn levels greater than or equal to 50 mg L(-1) had chronic toxicity symptoms after several days of exposure and did not measurably grow. Mineral analysis showed that Zn accumulated linearly in plant shoots in response to increasing Zn, despite the expression of varying levels of Zn toxicity symptoms. Total shoot S and SO(4)(2-) accumulated at amounts greater than the control when exposed to Zn levels greater than or equal to 25 mg L(-1) Zn; even though solution S did not vary among treatments. At the higher Zn concentrations, shoot S did not differ from the control. Additionally, SO(4)(2-) was responsible for the nearly all the S measured regardless of Zn exposure. This suggests that Zn uptake and accumulation differs from S when exposed to increasing Zn availability.