Root Growth and 14C-Translocation into the Roots of Maize (Zea mays L.) as influenced by local Nitrate Supply

A local nitrate supply to roots of maize causes increasing growth of the first order and the formation of higher order laterals. Number of first order laterals, however, remains unchanged. Labelling plants with ¹⁴CO₂ demonstrates a specific phloem unloading in the supply zone. It is suggested that phloem mobile phytohormones, especially auxins, lead to an endogenous shift in the phytohormone balance responsible for the morphogenetic effect of a local NO₃ · supply.