Transient growth responses of the primary roots of Zea mays.

1. The technique of streak photography was modified to use seven parallel cameras, each focused on an individual root in a guide holding flowing nutrient. Streak photographs representing displacement of points on the longitudinal axis of the root were projected on the table of an image plane digitizer. The displacement data are collected on cards by an IBM 526 key punch and processed by an IBM 360-65 computer. All graphic data were plotted by an EAI line plotter having a resolution of 600 lines per inch. 2. Roots of corn held at a temperature of 25°, a pH of 5.6, with constant oxygen concentration and basic nutrient composition, were subjected to step changes in oxygen and auxin (3-indoleacetic acid, IAA) concentrations. When O2 was lowered the response of the root consisted of a large reduction in growth rate followed by a series of oscillations with a period of about 30-50 min. Step changes in IAA from 0-10(-8)M (or less) resulted in heavily dampened oscillatory responses as well as reduction in growth rate. 10(-7) M IAA, however, elicited the initial inhibition followed by full recovery of growth rate after a few hours.