Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

IAA-Induced Growth Responses of Decapitated Corn Seedlings: Indications of Two Apparent Adaptations with a Possible Role in Gravitropism

Ronald D. Hatfield and Clifford E. LaMotte
Plant Physiology
Vol. 74, No. 2 (Feb., 1984), pp. 302-306
Stable URL: http://www.jstor.org/stable/4268456
Page Count: 5
  • Read Online (Free)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
IAA-Induced Growth Responses of Decapitated Corn Seedlings: Indications of Two Apparent Adaptations with a Possible Role in Gravitropism
Preview not available

Abstract

The vertical growth responses of corn seedlings (Zea mays L. Mo17 × B73) were determined over an 8-hour period. When seedlings were decapitated 3 millimeters from the coleoptile's tip and supplied with indole-3-acetic acid (IAA) in 1.5% agar blocks, the response was dependent both on time and IAA concentration. The dose-response curves changed in shape and magnitude depending on the total time of IAA application. High concentrations (>3.2 × 10-6 molar) initially produced high relative growth rates that decreased back to the intact rate (0.03 millimeter per hour per millimeter) after 3 hours. Low concentrations (<1.0 × 10-6 molar), or agar blocks without IAA, resulted in a rapid decrease from the intact rate to a level that stabilized at 0.01 millimeter per hour per millimeter until the growth rate began to recover after 3 to 4 hours. Intermediate concentrations produced responses similar to that of the intact organ, though some features of these responses were unique. The coleoptile curvature in response to gravity depended upon whether the coleoptiles were intact, decapitated, or decapitated and supplied with IAA. Coleoptiles decapitated and not supplied with IAA showed little or no curvature for 3 hours after decapitation. By this time an adaptation, evoked by the low IAA level, had developed and the coleoptiles began to curve steadily. When 1.0 or 3.2 × 10-6 molar IAA was supplied, curvature was initiated within the first 30 minutes and reached a maximum rate before decreasing and stopping after 3 to 4 hours. The sequence of events in response to these concentrations was similar to the intact sequence but the curvature rate was reduced to one-third to one-half. A model for the autotropic response involving an auxin concentration-dependent, growth-modulating mechanism capable of two modes of adaptation is described.

Page Thumbnails

  • Thumbnail: Page 
302
    302
  • Thumbnail: Page 
303
    303
  • Thumbnail: Page 
304
    304
  • Thumbnail: Page 
305
    305
  • Thumbnail: Page 
306
    306