Translocation of Mineral Ions

Translocation of Mineral Ions

Once mineral ions reach the xylem — by active uptake, passive uptake, or a combination — they travel further up through the stem and out to every part of the plant, riding along in the transpiration stream (the same upward flow of water driven by transpiration). The main "sinks" drawing in these minerals are the plant's actively growing regions: the apical and lateral meristems, young developing leaves, developing flowers, fruits and seeds, and storage organs. Minerals are unloaded from the transport stream at the fine endings of leaf veins, through a combination of diffusion and active uptake by the receiving cells.

Minerals are also frequently remobilised — withdrawn from one part of the plant and redirected to another — particularly from tissues undergoing senescence (ageing). Older, dying leaves export a large share of their mineral content to younger leaves before they die, and deciduous plants similarly withdraw minerals from leaves before shedding them in autumn. Some elements are readily remobilised this way — chiefly phosphorus, sulphur, nitrogen and potassium — while structural elements such as calcium are generally not remobilised once incorporated into plant tissue. …