Auxin deficiency at the onset on root growth in Allium cepa
Summary3-Indolylacetic acid (IAA) increased the length of the epidermis cells of onion roots during the initial stage of root growth, when cell length has not yet reached its maximum value, by up to 50% (10−11 M), while in the later, steady-state or dynamic equilibrium stage no promotive effects were present. It is suggested that the lesser elongation capacity of the cells at the onset of root growth is related to a deficiency in auxin while the steady-state phase is characterized by hormonal balance.
Growth components in Allium roots
SummaryThis paper reports results of a study of root growth, duration of the division cycle, and cell size for different intervals of root length, associated with different phases of growth, namely, from the onset of growth to the achievement of a steady state characterized by a constant rate of growth. The material is roots of Allium cepa.Steady-state kinetics of growth are achieved only when all components of growth reach a constant value. Although the cell flow remains constant from a root length of 8 mm onwards, the steady condition is only observed when the final size of the epidermal cells reaches its maximum and constant value (at about 12 mm of root length).The equation G=24×10-5 \N\φ·L is proposed to analyze the growth of Allium roots in its components. G is the growth rate (mm/24 hr), N the number of cells per column in the meristematic ribs, φ the rate of the cell cycle (the reciprocal of its duration x100), and L the average final size of the epidermal cells (in μ).
Effect of temperature and oxygen tension on root growth, cell cycle and cell elongation
SummaryThis paper reports the results of a study of root growth, the duration of the division cycle and the cell size in onion roots (Allium cepa) at different temperatures (5, 15, 25, 30, and 35° C) and at different oxygen tensions (2, 5, 10, and 20% at 25° C). The growth rate increases with the temperature up to a maximum between 25 and 30° C, while the division cycle shows a minimum duration between 30 and 35° C and the final size of the epidermic cells remains constant from 5 to 25° C decreasing from this temperature onwards.The oxygen tension shows a marked effect in conditioning the root growth. The growth rate increased the slower the nearer the oxygen tension was to the concentration found in the air. The division cycle appears to be strongly dependent on this environmental factor, whereas the final cell size is observed to be constant at all the oxygen tensions tested. There follows a discussion of the effects of the various environmental factors on root growth and on its components, namely cell formation and cell elongation.