Iodine uptake by spinach (Spinacia oleracea L.) plants grown in solution culture:: effects of iodine species and solution concentrations

A hydroponic experiment was carried out to investigate the effects of iodine species and solution concentrations on iodine uptake by spinach (Spinacia oleracea L.). Five iodine concentrations (0, 1, 10, 50 and 100 muM) for iodate (IO3-) and iodide (I-) were used. Results show that higher concentrations of I- (greater than or equal to 10 muM) had some detrimental effect on plant growth, while 103 had little effect on the biomass production of spinach plants. Increases in iodine concentration in the growth solution significantly enhanced I concentrations in plant tissues. The detrimental effect of I- on plant growth was probably due to the excessively high accumulation of I in plant tissues. The solution-tospinach leaf transfer factors (TFleaf, fresh weight basis) for plants treated with iodide were between 14.2 and 20.7 at different solution concentrations of iodide; TFleaf for plants treated with iodate decreased gradually from 23.7 to 2.2 with increasing solution concentrations of iodate. The distribution coefficients (DCs) of I between leaves and roots were constantly higher for plants treated with iodate than those treated with iodide. DCs for plants treated with iodide increased with increasing solution concentrations of iodide, while DCs for plants treated with iodate (around 5.5) were similar across the range of solution concentrations of iodate used in this experiment. The implications of iodine accumulation in leafy vegetables in human iodine nutrition are also discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.