A New Approach to Measure Gross CO2 Fluxes in Leaves. Gross CO2 Assimilation, Photorespiration, and Mitochondrial Respiration in the Light in Tomato under Drought Stress

Abstract

We developed a new method using 13 CO 2 and mass spectrometry to elucidate the role of photorespiration as an alternative electron dissipating pathway under drought stress. This was achieved by experimentally distinguishing between the CO 2 fluxes into and out of the leaf. The method allows us to determine the rates of gross CO 2 assimilation and gross CO 2 evolution in addition to net CO 2 uptake by attached leaves during steady-state photosynthesis. Furthermore, a comparison between measurements under photorespiratory and non-photorespiratory conditions may give information about the contribution of photorespiration and mitochondrial respiration to the rate of gross CO 2 evolution at photosynthetic steady state. In tomato (Lycopersicon esculentum Mill. cv Moneymaker) leaves, drought stress decreases the rates of net and gross CO 2 uptake as well as CO 2 release from photorespiration and mitochondrial respiration in the light. However, the ratio of photorespiratory CO 2 evolution to gross CO 2 assimilation rises with water deficit. Also the contribution of re-assimilation of (photo) respiratory CO 2 to gross CO 2 assimilation increases under drought.Water deficit limits plant growth and productivity because it decreases net CO 2 assimilation due to reduced stomatal conductance for CO 2 and/or because of non-stomatal effects like inhibition of enzymatic processes by changes in ionic or osmotic conditions (Lawlor, 1995). At high light intensities the lowered consumption of redox equivalents in the Calvin cycle makes it necessary to degrade photosynthetic electrons in processes other than CO 2 fixation to avoid photo-inhibition. Sharkey et al. (1988) showed that the activity of photosystem II can be regulated in a way that the rate of electron transport matches the capacity of the electron consuming reactions and that linear electron transport depends not only on light intensity and CO 2 concentration but also on the O 2 concentration. Oxygen can function as alternative electron acceptor directly in the Mehler reaction or indirectly in photorespiration (Badger, 1985).By combined measurements of O 2 and CO 2 gas exchange it should be possible to investigate the distribution of photosynthetic electrons between the electron consuming reactions CO 2 assimilation, photorespiration, and Mehler reaction (Haupt-Herting, 2000). The influence of drought stress on photosystem II activity, gross O 2 evolution, and gross O 2 uptake in tomato (Lycopersicon esculentum Mill. cv Moneymaker) plants has been published elsewhere (Haupt-Herting and Fock, 2000). This paper deals with the corresponding carbon fluxes determined by a new CO 2 gas exchange method.

Mitochondrial Alternative Oxidase Maintains Respiration and Preserves Photosynthetic Capacity during Moderate Drought in Nicotiana tabacum

“…There is less consensus in the literature of how drought impacts respiration rate (Atkin and Macherel, 2009). In some cases, drought was reported to have little or no effect on respiration rate (Ribas-Carbo et al, 2005;Giraud et al, 2008;Gimeno et al, 2010), whereas other studies reported decreases (Haupt-Herting et al, 2001;Haupt-Herting and Fock, 2002;Taylor et al, 2005;Vassileva et al, 2009;Galle et al, 2010;Ayub et al, 2011) or even increases (Bartoli et al, 2005;Feng et al, 2008;Hummel et al, 2010;Begcy et al, 2011). We found that both R D and R L tended to be lower (by about 27%) in moderate drought-stressed than well-watered wild-type N. tabacum (Fig.…”

Mitochondria Provide the Main Source of Cytosolic ATP for Activation of Outward-rectifying K+ Channels in Mesophyll Protoplast of Chlorophyll-deficient Mutant Rice (OsCHLH) Seedlings

“…The rates of net O 2 uptake, which are nearly identical to net CO 2 release, are comprised of O 2 evolution in the Hill reaction of PS II, O 2 consumption by the Mehler reaction and the glycolytic pathway, and O 2 consumption in mitochondrial respiration in the light, whereas photorespiratory CO 2 evolution is accompanied by CO 2 uptake in the Calvin cycle and CO 2 release from mitochondrial respiration (61). Based on these facts and the photosynthetic properties of the OsCHLH mutant it is possible that respiration in the light may depend on the amount of photosynthetic primary products (61,62), which the mutants are expected to lack because there is no photosynthetic CO 2 fixation. This could explain, as it does in drought-stressed plants (61) the substantial decrease of mitochondrial O 2 uptake and CO 2 release in the OsCHLH mutant in the light.…”

Influence of transient shade periods on the effects of drought on photosynthesis, carbohydrate accumulation and lipid peroxidation in sunflower leaves

“…Therefore, even if photorespiration had been increased during the period of low g, it should be expected to return to control values following re-watering and concomitant stomatal reopening. As to mitochondrial respiration in the light, Haupt-Herting et al (2001) reported that this process is inhibited by water stress in tomato plants, but to our knowledge, dark respiration in re-watered plants has not been assessed so far. However, increased demand for maintenance respiration may be expected during re-watering, in order to support the repair of dehydration-induced damages, including oxidative damage to lipid, as apparently happened in the present experiments, taking into account the observed increase in foliar levels of MDA (Fig.…”