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Published on August 20, 2008; 10.1104/pp.108.127324

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Received July 30, 2008
Accepted August 13, 2008

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

Christoph Andreas Lehmeier , Fernando Alfredo Lattanzi *, Rudi Schaufele , Melanie Wild , and Hans Schnyder

Lehrstuhl fur Grunlandlehre, Department fur Pflanzenwissenschaften, Technische Universitat Munchen, Am Hochanger 1, D-85350 Freising-Weihenstephan, Germany

* Corresponding author; email: lattanzi{at}wzw.tum.de.

The substrate supply system for respiration of the shoot and root of a perennial grass was characterized in terms of component pools, and pool's functional properties: size, half-life (t1/2) and contribution to respiration of the root and shoot. The investigations were performed with Lolium perenne L. growing in constant conditions with continuous light. Plants were labeled with 13CO2/12CO2 for periods ranging from 1 h 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 approx. 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%). Pool's half-lives and relative sizes were also near-identical in shoot and root (t1/2 <15 min, ~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.






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