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Estimation of Photorespiration Based on the Initial Rate of Postillumination CO₂ Release: II. Effects of O₂, CO₂ and Temperature

Richard B. Peterson
Plant Physiology
Vol. 73, No. 4 (Dec., 1983), pp. 983-988
Stable URL: http://www.jstor.org/stable/4268378
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Estimation of Photorespiration Based on the Initial Rate of Postillumination CO₂ Release: II. Effects of O₂, CO₂ and Temperature
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Abstract

An open system associated with an infrared gas analyzer was employed to study transients in CO2 exchange generated upon darkening preilluminated leaf discs of tobacco (Nicotiana tabacum vars John Williams Broadleaf and Havana Seed). An empirical formula presented previously enabled prediction of the analyzer response under nonsteady state conditions as a function of time and of the leaf CO2 exchange rate. A computer was used to evaluate parameters of the leaf CO2 release rate to provide an estimate of the initial rate of postillumination CO2 evolution and to produce maximal agreement between predicted and observed analyzer responses. In 21% O2, the decline in rate of CO2 evolution upon darkening followed first order kinetics. Initial rates of CO2 evolution following darkening were relatively independent of the prior ambient CO2 concentrations. However, rates of photorespiration expressed as a fraction of net photosynthesis declined rapidly with increasing external CO2 concentration at 21% O2. Under normal atmospheric conditions, photorespiration was 45 to 50% of the net CO2 fixation rate at 32°C and high irradiance. The rapid initial CO2 evolution observed upon darkening at 21% O2 was absent in 3% O2. Rates of photorespiration under normal atmospheric concentrations of CO2 and O2 as measured by the postillumination burst were highly dependent upon temperature (observed activation energy = 30.1 kilocalories per mole). The results are discussed with respect to previously published estimates of photorespiration in C3 leaf tissue.

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