MOVEMENT OF AMYLOPLASTS IN ROOT CAP CELLS OF GEOTROPICALLY SENSITIVE ROOTS

The root cap of Lepidium sativum under our culture conditions was found to contain 7 (or occasionally 8) storeys of starch‐containing cells. In the youngest one (or two) of these storeys the amyloplasts are small and the cells appear embryonic. In the 6 non‐embryonic storeys the amyloplasts are large. Upon inversion of the root, the amyloplasts in the 3 youngest of the 6 non‐emhryonic storeys start falling toward the opposite end of the cell at about 72 μ per h (at 21 C), hut they maintain this speed for only 6 to 12 min, after which they virtually come to a stop. As a result, it takes 10 to 12 min before any of the amyloplasts get approximately as close to the ceiling as they were to the floor before the inversion; and this is true only of the 2 youngest of the non‐embryonic storeys. When the root is placed horizontal, whether coming from the normal or the inverted position, the amyloplasts reach the lower, longitudinal wall in 15 min or less. The positions of the amyloplasts in the cells of the 3 oldest starch‐containing storeys are erratic and show little, if any, dependency on the preceding time of inversion. Copyright © 1968, Wiley Blackwell. All rights reserved