Ion Uptake and Root Age

Abstract

IT has been widely assumed that the translocation of nutrient ions to plant shoots occurs chiefly from young extending zones of tissue within 1 cm of the apical meri-stems of roots. The rapid accumulation of ions which can occur in this zone^1–3, its high metabolic activity^4–7 and the fact that considerable thickening of the endodermis seems to create a barrier to the entry of ions into the stele^4,8 have been regarded as evidence for this. Results of more recent studies have indicated, however, that translocation occurs to an approximately constant extent over the apical 6 cm of cereal roots^9,10 despite the progressive development of the endodermis⁸. These findings encourage the study of nutrient absorption and translocation by older parts of the root axis. Information on this question is relevant both to the elucidation of the effects of the structure of roots on their capacity to absorb ions, and to the assessment of the limitations which the rate of ionic diffusion in soil^11,12 may impose on plant nutrition.