Exogenous supply of NA and zinc uptake. A and B, The concentrations of ⁶⁷Zn, a stable isotope of zinc, in shoots (A) and roots (B) of A. thaliana grown hydroponically under excess zinc treatments at the indicated concentrations supplied with 50 μm  NA (+NA) or without NA (−NA) were determined using HR-ICP-MS. The samples were collected after treatment for 24 h. Data are the mean ± sd of four replicates with four pooled plants each. Asterisks denote significant differences compared with no NA treatment. *P < 0.05 and **P < 0.01 by the Student’s t test. DW, Dry biomass.