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.
The Development of the Maize Root System: Role of Auxin and Ethylene
The maize primary root is a cylindrical structure formed by consecutive zones: (a) the root apex contains the apical meristem, where cell divisions occur; (b) the elongation zone in which cells stop dividing and start to elongate; and (c) the maturation zone, where cells reach their definitive lengths, cell differentiation begins, and lateral roots initiate. In the root, three main tissue systems can be distinguished: the epidermis, the cortex, and the vascular cylinder. The first layer of the vascular cylinder is the pericycle. Cell cycle activation in pericycle cells is clearly connected with lateral root initiation.
Effect of osmotic pressure on root growth, cell cycle and cell elongation
SummaryThe paper reports a study of root growth, the duration of the cell division cycle and cell size, inAllium cepa roots grown in mannitol solution, with osmotic pressures of 0–16 atm., at 25° C, with aeration. Root growth decreases markedly as the osmotic pressure rises, at 12 atm. being about 35% of what it is at 0 atm. The rate of the cell cycle, ϕ, expressed as the percentage of cells passing through any given point in the cycle in one hour, is a roughly linear function of the osmotic pressure, and at 12 atm. is reduced to 80% of what it is at 0 atm. The reaction of the cell size to osmotic pressure is similar to that of the growth. The relative values of the two diverge progressively as the osmotic pressure increases and at 12 atm. the elongation of the cells has dropped to 40% of normal.The data obtained agree with those given by the equationG = K · ϕ · L, in whichK is a constant, ϕ is the rate of the cycle (reciprocal of its duration) andL the average size of the mature epidermal cells.