Lateral Root Anlage Development in Excised Roots of Vicia faba L., Pisum sativum L., Zea mays L. and Phaseolus vulgaris L.

Abstract

The development of lateral root primordia has been investigated in excised roots of Vicia faba, Pisum sativum, Zea mays and Phaseolus vulgaris cultured in White's medium supplemented with 2 per cent sucrose and compared with previously published data on such development in primaries of the corresponding intact plants (control roots). Primordia were produced in each batch of excised roots over the 6 day culture period but at a lower rate (number day−1) than in the controls. Such primordia in cultured roots of Zea and Phaseolus completed their development and grew out as lateral roots over a period similar in length to that found in the controls, but with a cell number of only about 33 per cent of that attained at the time of secondary emergence in the primaries of the latter roots. These lower cell numbers were at least partly a reflection of increases in mean cell doubling time over the period of anlage development investigated in the excised roots relative to the corresponding values found in the controls. Primordia initiated in excised roots of Pisum and Vicia did not complete their development in culture, i.e. no lateral roots emerged and arrest took place with cell numbers of only 37 (Pisum) and 17 (Vicia) per cent of the numbers determined at the time of secondary root emergence in the controls. Such arrested primordia had few nuclei in S and none in mitosis. Moreover, at least in Pisum, the frequency distribution of the relative DNA content of the nuclei in the latter primordia approximated that found in the apical meristem of primary roots following the establishment of the stationary phase under conditions of carbohydrate starvation. It has also been demonstrated in the course of these investigations that lateral root primordium development in all four species is at least biphasic and possibly triphasic.