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.
Transport of indoleacetic acid in intact roots of Phaseolus coccineus
SummaryIndoleacetic acid (IAA)-5-3H (2×10-9) was applied to intact roots of Phaseolus coccineus seedlings at the apex or 2 cm above the apex, and the movement of IAA-3H and its metabolites traced by sectioning and chromatography. Basipetal movement of label occurred for 2 cm or less, declining exponentially, and the amount increased with time. Acropetal transport from above the apex showed quantitatively less movement of radioactivity. After a 6h treatment period a decline of label occurred in the first 0.5cm, below which there was a long distance movement of small amounts of label, mainly in IAA, towards the apex where the label concentrated by a factor of approximately 2. Short-distance basipetal movement consisted of about equal amounts of IAA and metabolites, and only metabolites were found in areas more basipetal than 2cm. Label from solutions of sucrose-14C and 3H2O followed the same general pattern of movement as label from IAA-3H, except that acropetal movement of water showed a steady decrease in the amount of label as the distance from the area of application increased. The short distance basipetal transport of label with the breakdown of IAA-3H indicates that the extent of basipetal movement was limited by catabolic processes. The acropetal pattern of IAA-3H movement with the concentration of the transported material close to the apex, is possibly the result of transport in the phloem.
The Effects of Temperature on the Durations of the Different Stages of Cell Division in the Root-tip
A new technique for determining the durations of the different phases of division is described. It is shown that at 15o C. the mean durations of the several phases in the root tip of the pea are as follows : interphase 23 hours ; prophase 2 hours ; metaphase 25 minutes; anaphase 5 minutes; telophase 22 minutes. The effects of different temperatures have been determined, and it is shown that all stages are accelerated by an increase in temperature from 15o to 25° C., the ratios of the durations at the two temperatures being about 2-0 or slightly less. It is suggested that since interphase is the longest stage of the division cycle, in terms of growth effects on this stage are the most significant.