Tissue specificity of assimilation and transport of nitrogen in the root ofZea mays L. seedlings. III. Interaction of radial and longitudinal transport

Roots obtained from 4-day maize seedlings were allowed to absorb uniformly labelled¹⁴C-suorose only with their middle part while the apical and basal parts did not contact the medium. The amino acids and their amides produced in the cortex at the expense of nitrates and the¹⁴C-sucrose carbon moved radially to the stele where they were selectively distributed in the polar directions of transport. “Primary” amino acids moved predominantly in the apical direction while amides and basic amino acids were transported mainly in the opposite direction. When the nutrient medium was devoid of nitrogen sources, the amino acids entering the stele from the cortex were transported mostly to the root tip, indicating a significant role of young tissues in consuming organic nitrogen compounds when they are in short supply in the root.