Root cap structure and cell production rates of maize (<em>Zea mays</em>) roots in compacted sand

To assess the influence of mechanical impedance on cell fluxes in the root cap, maize (Zea mays) seedlings were grown in either loose or compacted sand with penetration resistances of 0.2 MPa and 3.8 MPa, respectively. Numbers of cap cells were estimated using image analysis, and cell doubling times using the colchicine technique. There were 5930 cells in the caps in the compact and 6900 cells in the loose control after 24 h growth in sand. Cell production rates were 2010 cells d-1 in compact and 1570 cells d-1 in loose sand. These numbers represent accumulations of 4960 and 3540 detached cells d-1 around the cap periphery following the two types of treatment. The total number of detached cells was estimated as sufficient to completely cover the whole root cap in the compact sand, but only 11% of the root cap in the loose sand. In conclusion, mechanical impedance slightly enhanced meristematic activities in the lateral region of the root cap. The release of extra border cells would aid root penetration into the compact sand.