Vanadium uptake and transport in higher plants
The uptake and transport of vanadium in several higher plant species has been examined. Studies utilizing excised Hordeum roots have revealed the uptake patterns of two different ionic species of vanadium (V02+ and V03) to be similar. Both ionic forms exhibited a large extracellular component in their uptake. This extracellular component was shown to be exchangeable with a number of agents but was most effectively removed by a post uptake treatment in a solution of chromium(VI). This removal of extracellular vanadium by chromium was considered to be a genuine exchange process although the mechanism involved is unclear. The effect of temperature, pH, metabolic inhibitors and complexing agents were also examined and found to be similar for the two ionic forms considered. Concentration dependent uptake of the two ionic forms was also examined. Saturation kinetics were observed when a wide concentration range of vanadium (0.1-5.0 MM) was employed. These results were considered suggestive of conversion of vanadium to a common form within root tissues. Whole plant studies utilizing Zea and Vicia also revealed highly similar uptake patterns for the two different ionic species of vanadium. Irrespective of the ionic form of vanadium supplied to the plant marked retention of vanadium within the root tissues was observed. Analysis of vanadium root-shoot transport patterns in plants supplied with different ionic species of vanadium suggested that a common form of vanadium was being transported in both cases. Possible interactions between vanadium and other ions within the plant are briefly considered. ESR studies utilizing Hordeum clearly illustrated the ability of plant roots to reduce pentavalent vanadium to the tetravalent form. Evidence from all three lines of study is discussed and considered to support the suggestion that vanadium within plant roots exists in the reduced tetravalent form. This is thought to be of prime importance in determining the mobility of vanadium within plant tissues.