Duration of lateral root formation in maize seedlings as affected by diverse factors

Abstract

One of the important elements of root branching in plants is lateral root formation. The time of lateral root formation, defined as the time from the start of cell division in the pericycle to lateral root appearance (Tlr), represents an essential dynamic characteristic of root branching. The variability of Tlr under various environmental conditions is unknown. The effect of diverse factors on Tlr was analysed in maize (Zea mays cv. Sterling) seedlings grown in vitro. These factors were X-radiation and about 1000 different chemical compounds. In control roots, Tlr ranged from 45 to 52 hours. Most of the chemicals tested did not influence Tlr. In spite of strong inhibition of main root growth by some of them, Tlr remained constant. With increasing root length, the length of the unbranched part of the root (Lubp) increased linearly. Tlr was almost independent of the root growth rate. The variation in Lubp depended mainly on the variation in root growth rate. Neither the decline in apical dominance nor direct action of substances on lateral root development caused shortening of the Lubp. Only cytostatic chemicals, gametocides, and X-radiation prevented the formation of lateral roots and increased Tlr at low doses or concentrations. This effect was caused by inhibition of cell divisions in lateral root primordia (X-ray radiation and cytostatics) or inhibition of lateral root emergence (gametocides). A simple test for cytostatic screening based on the inhibition of root branching is proposed. The data indicated that lateral root development in higher plants is a very stable process resistant to many inhibiting factors. This stability, in terms of time, also suggested that lateral roots have a great ability to adapt to environmental changes