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WHOLE PLANT AND ECOPHYSIOLOGY

Root and Shoot Respiration of Perennial Ryegrass Are Supplied by the Same Substrate Pools: Assessment by Dynamic ¹³C Labeling and Compartmental Analysis of Tracer Kinetics^1,[OA]

Lehrstuhl für Grünlandlehre, Department für Pflanzenwissenschaften, Technische Universität München, D–85350 Freising-Weihenstephan, Germany

The substrate supply system for respiration of the shoot and root of perennial ryegrass (Lolium perenne) was characterized in terms of component pools and the pools' functional properties: size, half-life, and contribution to respiration of the root and shoot. These investigations were performed with perennial ryegrass growing in constant conditions with continuous light. Plants were labeled with ¹³CO₂/¹²CO₂ for periods ranging from 1 to 600 h, followed by measurements of the rates and ¹³C/¹²C ratios of CO₂ respired by shoots and roots in the dark. Label appearance in roots was delayed by approximately 1 h relative to shoots; otherwise, the tracer time course was very similar in both organs. Compartmental analysis of respiratory tracer kinetics indicated that, in both organs, three pools supplied 95% of all respired carbon (a very slow pool whose kinetics could not be characterized provided the remaining 5%). The pools' half-lives and relative sizes were also nearly identical in shoot and root (half-life < 15 min, approximately 3 h, and 33 h). An important role of short-term storage in supplying respiration was apparent in both organs: only 43% of respiration was supplied by current photosynthate (fixed carbon transferred directly to centers of respiration via the two fastest pools). The residence time of carbon in the respiratory supply system was practically the same in shoot and root. From this and other evidence, we argue that both organs were supplied by the same pools and that the residence time was controlled by the shoot via current photosynthate and storage deposition/mobilization fluxes.

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: Fernando Alfredo Lattanzi (lattanzi{at}wzw.tum.de).

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.127324

^* Corresponding author; e-mail lattanzi{at}wzw.tum.de.

Received July 30, 2008; accepted August 13, 2008; published August 20, 2008.