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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Reciprocal Leaf and Root Expression of AtAmt1.1 and Root Architectural Changes in Response to Nitrogen Starvation^1,[W]

Department of Biology, Washington University, St. Louis, Missouri 63130

Nitrogen is an essential macronutrient for plant growth and survival. Here, the temporal and spatial sensing of nitrogen starvation is analyzed in Arabidopsis (Arabidopsis thaliana). The promoter for the high-affinity ammonium transporter, AtAmt1.1, is shown to be a valid indicator for nitrogen status in leaves and roots. An AtAmt1.1-Gal4 transgene using three 5x upstream activating sequence-driven reporters (luciferase, green fluorescent protein, and -glucuronidase) facilitated in vivo profiling at the whole-plant and cellular levels. The effects of nitrogen supply, light duration, light intensity, and carbon on the expression of the AtAmt1.1 gene in the roots and aerial tissues are reported. Under nitrogen starvation, high expression is observed in the roots and, under nitrogen-sufficient conditions, high expression is observed in the leaves. This reciprocal regulation of AtAmt1.1 was confirmed by quantitative reverse transcription-polymerase chain reaction, which was also used to quantitate expression of the five other Amt genes in Arabidopsis. Although some of these show tissue specificity (roots or leaves), none exhibit reciprocal regulation like the AtAmt1.1-encoded high-affinity transporter. This robust reciprocal expression suggests that Arabidopsis undergoes rapid resource reallocation in plants grown under different nitrogen supply regimens. Ultimately, nitrogen starvation-mediated reallocation results in root architectural restructuring. We describe the precise timing and cellular aspects of this nitrogen limitation response.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Robert G. Kranz (kranz{at}biology.wustl.edu).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.088500

^* Corresponding author; e-mail kranz{at}biology.wustl.edu; fax 314–935–4432.

Received August 19, 2006; accepted October 25, 2006; published November 3, 2006.

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