Roots typically respond to localized nitrate patch in soils by enhancing lateral root growth. Using maize, Zea mays, grown in a split-root system, Liu et al. quantify auxin levels in the roots and examine its polar transport by the movement of labelled 3H-IAA. They find that localized nitrate supplied to one half of the root system reduces shoot-to-root auxin transport and decreases the auxin concentration in the roots to a level more suitable for lateral root growth. However, alteration of root auxin level alone is not sufficient to stimulate lateral root growth.