LEAD UPTAKE, DISTRIBUTION, AND REMOBILIZATION IN CUCUMBER

Mobility and distribution of lead (Pb) were investigated in cucumber ( Cucumis sativus L.) grown in solution culture. Based on the observatio n that Pb uptake is influenced by the chemical form of iron (Fe) (comp lexed or ionic) in the solution, Fe distribution was also determined. Iron concentration was even in the stem (separated to internodes) and petioles but slightly increased at the shoot tip while Pb concentratio n decreased upwards. In the leaves Fe concentration decreased upwards (whereas in the control it increased a little at the youngest leaves) while Pb concentration increased to the largest leaves then decreased towards the shoot tip. It is suggested that the distribution of Pb in cucumber is passive process and it accumulates in the apoplast while F e distribution is determined by the requirements of synthetic processe s in young or photosynthesizing tissues. Lead probably lowers Fe trans port into the symplast in the leaves causing slight chlorosis at the y oungest leaves. In the plants that were loaded with Pb, decapitated an d rooted again in Pb-free culture solution we found no significant rem obilization of Pb which supports that Pb binds strongly to the binding sites in the apoplast or is detoxified in an immobile form.