Journal of Experimental Botany, Vol. 51, No. 347, pp. 1089-1097,
June 2000
© 2000 Oxford University Press
Respiratory costs and rate of protein turnover in the roots of a fast-growing (Dactylis glomerata L.) and a slow-growing (Festuca ovina L.) grass species
1 Plant Ecophysiology, Faculty of Biology, Utrecht University, PO Box 80084, NL-3508 TB Utrecht, The Netherlands
2 Institut für Botanik, University of Münster, Schlossgarten 3, D-48149 Münster, Germany
3 Plant Sciences, Faculty of Agriculture, The University of Western Australia, Nedlands WA 6907, Australia
Protein turnover is generally regarded as one of the most important maintenance processes in plants in terms of energy requirements. In this study, the contribution of protein turnover to the respiratory costs for maintenance in the roots of two grass species, the fast-growing Dactylis glomerata L. and the slow-growing Festuca ovina L., is evaluated. Plants were grown under controlled-environment conditions in a nutrient solution to which 
was added at a relative addition rate of 0.2 and 0.1 mol N mol-1 N already present in the plant d-1 for D. glomerata and F. ovina, respectively, so as to obtain a steady exponential growth rate close to the plants' maximum relative growth rate. Pulse-chase labelling with 14C-leucine was used to determine the rate of protein turnover in the grass roots. The rate of turnover of the total protein pool did not differ significantly between the two species. The protein degradation constant in D. glomerata and F. ovina was 0.156 and 0.116 g protein g-1 protein d-1, respectively, which corresponds with a total protein half-life of 4 d and 6 d. Assuming specific respiratory costs for protein turnover of 148 mmol ATP g-1 protein, the estimated respiratory costs for protein turnover in the roots were 2.8 and 2.4 mmol ATP g-1 root DM d-1 in D. glomerata and F. ovina, respectively. Both the fast- and the slow-growing grass spent between 22–30% of their daily ATP production for maintenance on protein turnover, which corresponds to 11–15% of the total root ATP production per day. Note that the data presented in this abstract are based on the assumption that 50% recycling of the 14C-labelled leucine took place in the roots of both grass species.
Key words: Dactylis glomerata L., Festuca ovina L., maintenance, protein turnover, relative growth rate, specific respiratory costs.
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