© 1995 Oxford University Press
RESEARCH-ARTICLE |
Function and contribution of the root tip in the induction of NO3– uptake along the barley root axis
Pflanzenphysiologisches Institut, University of Göttingen Untere Karspüle 2, D-37073 Göttingen, Germany
1 To whom correspondence should be addressed: Fax:+49551 397823
The seminal roots of N-free-grown barley seedlings were able to take up NO3– immediately upon initial exposure; the uptake rate in the tip was half of that in the older root zones (middle and base). A lag of 60 min was required in all root zones before the uptake rates started to increase during induction with external NO3–. This increase could be prevented by the addition of pFPA; we thus assume that additional NO3– transport proteins were synthesized during NO3– induction. During the time-course of NO3– induction different uptake rates were measured in morphologically different regions of the tip (1 mm segments) indicating a regulation of NO3– induction on a narrow local scale.
In NO3– grown plants, NO3– uptake as well as NO3– content increased basipetally along the root axis concomitantly with increasing vacuolization of the cells. Although NO3– uptake into the tip was only half of that into the older root zones, this NO3– uptake was very important for the entire root. Firstly, it provided the substrate for protein biosynthesis in the meristematic region: nitrate reductase activity and total soluble protein were highest in the first apical mm of the tip. Secondly, 3% of the NO3– taken up by the tip was found in the base where it induced NO3– uptake: NO3– was translocated almost exclusively basipetally and as little as 20nmolg–1 root fr. wt. translocated from the tip were sufficient for acceleration of NO3– induction in the root base of N-free-grown plants. This clearly shows that the induction of NO3– uptake does not depend exclusively on the availability of external NO3–, but can be mediated also with internally translocated NO3–.The root tip, therefore, may be considered the NO3– sensing region of the root.
Key words: Barley, Hordeum vulgare L, internal NO3–, NO3– uptake, root zones
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  B. G. Forde Is it good noise? The role of developmental instability in the shaping of a root system J. Exp. Bot., October 1, 2009; 60(14): 3989 - 4002. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. J. BLOOM, J. FRENSCH, and A. R. TAYLOR Influence of Inorganic Nitrogen and pH on the Elongation of Maize Seminal Roots Ann. Bot., May 1, 2006; 97(5): 867 - 873. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W.M. Sullivan, Z. Jiang, and R. J. Hull Root Morphology and Its Relationship with Nitrate Uptake in Kentucky Bluegrass Crop Sci., May 1, 2000; 40(3): 765 - 772. [Abstract] [Full Text]
|
|