The mitochondrial respiration during photosynthesis is difficult to measure
and is indirectly estimated mainly in C 3 plants. Loreto
et al. [(1999)
Australian Journal of Plant Physiology
26, 733–736] 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 (0.1–0.4 ppm or 0.2–0.4 µmol m –2
s –1 ) in a wide range of leaf temperatures and light intensities, but
increased at light intensities below 200 µmol m –2 s –1 and
at temperatures above 42°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°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.
Genotypic variation of photosynthetic gas exchange and stomatal traits in some traditional rice (Oryza sativa L.) landraces from Koraput, India for crop improvement
