Uptake and translocation of fluoride in Helianthus annuus L. grown in sand culture

In Helianthus annuus seedlings grown in sand culture for 5 wk, the concentration of fluoride in the root and shoot was generally proportional to the concentration in the substrate. Highest concentrations were present in the roots and the concentrations in the leaves decreased acropetally. In a more detailed 6 wk study, the dynamics of uptake and translocation differed markedly. Whereas the total fluoride in the plant increased steadily in proportion to increased root dry weight, the amount translocated to the shoot each wk was reduced to almost zero after 4 wk. The fluoride in the shoot accumulated initially in the most physiologically active leaves. It appears, therefore, that the acropetal pattern of leaf accumulation is a function of leaf age rather than of position on the stem. The dynamics of accumulation in leaves suggested that a portion of the fluoride in a senescing leaf was retranslocated to younger leaves. Thus, although there was an increase in the immobility of the fluoride in the root over the study period, a portion of the fluoride in the shoot could be translocated from older to younger leaves.