Effect of ambient water volume on root growth, cell cycle duration, and mitotic synchrony during germination and seedling growth of Vicia faba

The relationship between root length, time of onset of mitotic activity, and the degree of synchrony of cells initiating mitosis was studied in germinating seed and seedlings of Vicia faba. These three parameters are related, but their relationship changes (1) with time during germination and seedling growth, and (2) in response to alterations in the volume of ambient water. Beans sown in 5 mm of water for 0–24 h gave better root growth and higher mitotic indices, at 68 h, than beans sown in 10 or 20 mm of water: conditions during the first 24 h after sowing influence growth at later times. Beans were also grown, from 24 to 70 h, in moistened sand or vermiculite–perlite (20 to 50 mL of water/100 mL of substrate). A well-defined optimum volume of water was identified; it gave the highest mean mitotic index (MI) and the greatest mean root length. Supra-optimal volumes of water resulted in an inhibition of root growth and a reduction in MI. Variation in the ambient water volume affects (i) root growth; (ii) ...