Abstract
The kinetics of vanadium absorption by excised barley (Hordeum vulgare L., cv. Eire) roots were investigated with respect to ionic species of V in solution, time and concentration dependence, Ca sensitivity, and interaction with various anions, cations, and pH levels. The role of metabolism in V absorption was also studied using anaerobic treatment (N(2) gas) and chemical inhibitors (NaN(3), KCN, or 2,4-dinitrophenol). Approximately one-third of the labeled V initially taken up by excised roots was desorbed to a constant level after 45 min in unlabeled V solutions. The rate of absorption of labeled V from 5 mum NH(4)VO(3) solutions containing 0.5 mm CaSO(4) was constant for at least 3 hours. Omission of Ca resulted in a 72% reduction in V uptake when compared to controls with 0.5 mm CaSO(4). The rate of uptake of V was highest at pH 4 but dropped to a very low level at pH 10. It was relatively constant between the pH levels of 5 and 8 at which the VO(3) (-) ion is the predominant ionic species in solution. The rate of absorption of V was followed as a function of concentrations from 0.5 to 100 mum NH(4)VO(3). It was found to be a linear function of concentration and did not follow saturation kinetics. Absorption experiments carried out with labeled V from either N(a)VO(3) or NH(4)VO(3) sources gave similar results. No anion studied (i.e. HPO(4) (2-), HAsO(4) (2-), MoO(4) (2-), SeO(4) (2-), SeO(3) (2-), CrO(4) (2-), BO(3) (3-), No(3) (-), and Cl(-)) interfered appreciably (i.e. less than 30% inhibition) with the absorption of labeled V. Anaerobic treatment of absorption solution with N(2) gas did not inhibit V absorption by excised roots. The results obtained using chemical inhibitors were not consistent. It was concluded that V is not actively absorbed by excised barley roots.