
TY  - JOUR
A1  - Loreto, Francesco 
A1  - Velikova, Violeta 
A1  - Di Marco, Giorgio 
T1  - Respiration in the light measured by <emph type="7">12</emph>CO <emph type="8">2</emph> emission in <emph type="7">13</emph>CO <emph type="8">2</emph> atmosphere in maize leaves
JF  - Functional Plant Biology
JO  - Functional Plant Biol.
Y1  - 2001
VL  - 28
IS  - 11
SP  - 1103
EP  - 1108
KW  - 
UR  - https://doi.org/10.1071/PP01091 
N2  - The mitochondrial respiration during photosynthesis is difficult to measure and is indirectly estimated mainly in C 3 plants. Loreto et al. &#91;(1999) Australian Journal of Plant Physiology 26, 733&#8211;736] have shown that the emission of 12 CO 2 from illuminated leaves exposed to air containing 13 CO 2 measures photorespiration and mitochondrial respiration in C 3 leaves. This method was used to measure the mitochondrial respiration in illuminated maize leaves. The 12 CO 2 emission was steady after 30 s, a time sufficient to label the CO 2 leakage from bundle sheath cells with 13 CO 2 , but not the mitochondrial respiration in the light. The emission was low (0.1&#8211;0.4 ppm or 0.2&#8211;0.4 &#181;mol m &#8211;2 s &#8211;1 ) in a wide range of leaf temperatures and light intensities, but increased at light intensities below 200 &#181;mol m &#8211;2 s &#8211;1 and at temperatures above 42&#176;C. At 120 s after labelling, the leaf was darkened and the emission rapidly matched the mitochondrial respiration measured by gas exchange. The emission of 12 CO 2 in the light was inversely correlated with photosynthesis. This suggested that most of the respiratory CO 2 was refixed by photosynthesis. The amount of refixed intercellular 12 CO 2 was calculated from gas-exchange parameters. It was 60 to 90% of the tota l12 CO 2 in leaves illuminated and exposed to temperatures below 42&#176;C. In leaves with reduced photosynthesis because of exposure to higher temperatures or low light, the 12 CO 2 refixation decreased. The sum of refixed and emitted 12 CO 2 was close to the mitochondrial respiration in the dark. This suggested that in these leaves the mitochondrial respiration was not inhibited in the light. In salt- and water-stressed leaves, however, the sum of refixed and emitted 12 CO 2 was lower than mitochondrial respiration in the dark, suggesting that the mitochondrial respiration may be inhibited in the light. 
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