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WHOLE PLANT AND ECOPHYSIOLOGY

Dynamics of Light and Nitrogen Distribution during Grain Filling within Wheat Canopy^1,[OA]

INRA, UMR 1091 Environnement et Grandes Cultures, F–78 850 Thiverval-Grignon, France (J.B., B.A.); AgroParisTech, UMR 1091 Environnement et Grandes Cultures, F–78 850 Thiverval-Grignon, France (J.B., B.A.); INRA, UMR 1095 Génétique, Diversité et Ecophysiologie des Céréales, F–63 100 Clermont-Ferrand, France (P.M.); and Université Blaise Pascal, UMR 1095 Génétique, Diversité et Ecophysiologie des Céréales, F–63 100 Clermont-Ferrand, France (P.M.)

In monocarpic species, during the reproductive stage the growing grains represent a strong sink for nitrogen (N) and trigger N remobilization from the vegetative organs, which decreases canopy photosynthesis and accelerates leaf senescence. The spatiotemporal distribution of N in a reproductive canopy has not been described in detail. Here, we investigated the role of the local light environment on the spatiotemporal distribution of leaf lamina N mass per unit leaf area (SLN) during grain filling of field-grown wheat (Triticum aestivum). In addition, in order to provide some insight into the coordination of N depletion between the different vegetative organs, N dynamics were studied for individual leaf laminae, leaf sheaths, internodes, and chaff of the top fertile culms. At the canopy scale, SLN distribution paralleled the light gradient below the flag leaf collar until almost the end of grain filling. On the contrary, the significant light gradient along the flag leaf lamina was not associated with a SLN gradient. Within the top fertile culms, the time course of total (alive + necrotic tissues) N concentration of the different laminae and sheaths displayed a similar pattern. Another common pattern was observed for internodes and chaff. During the period of no root N uptake, N depletion of individual laminae and sheaths followed a first-order kinetics independent of leaf age, genotype, or N nutrition. The results presented here show that during grain filling, N dynamics are integrated at the culm scale and strongly depend on the local light conditions determined by the canopy structure.

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: Pierre Martre (pmartre{at}clermont.inra.fr).

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.124156

^* Corresponding author; e-mail pmartre{at}clermont.inra.fr.

Received June 5, 2008; accepted September 11, 2008; published September 17, 2008.