ISSN:
1365-3040
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
The angle at which an organ is maintained by gravit-ropism is characteristic of the organ, its developmental state and the prevailing environmental conditions. We propose that this angle be called the gravitropic set-point angle (GSA), defined as the angle with respect to the gravity vector (with a vertically downward orientation being 0°) at which an organ is maintained as a consequence of gravitropism. Studies of the gravitropic behaviour of organs from trailing plants show that the GSA is subject to developmental regulation. Depending on the developmental age and prevailing environmental conditions, the GSA of an organ can he set at any value between 0° and 180° The previously reported reversal of the sign of the gravitropic response in such organs, whether this is brought about developmentally or induced by light, represents the change from one common extreme (GSA = 180°, conventionally referred to as negative orthogravitropism) to another (GSA = 0°, or positive orthogravitropism). The concept of a variable gravitropic set-point offers a more unified view of all forms of gravitropic behaviour than has been advanced previously, and places a new constraint on models of gravitropism. Current models of gravitropism appear to be unable to explain either the ability of organs to change their orientation with respect to gravity as they develop, or the re-orientation that can be observed when some organs are exposed to new environmental conditions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-3040.1995.tb00205.x
