Oxygen Exchange in Leaves in the Light

Abstract

Photosynthetic 02 production and photorespiratory 02 uptake were measured using isotopic techniques, in the C3 species Hirschfeldia incana Lowe., Helianthus annuus L., and Phaseolus vulgaris L. At high CO2 and normal 02,02 production increased linearly with light intensity. At low 02 or low C02, 02 production was suppressed, indicating that increased concentrations of both 02 and CO2 can stimulate 02 production. At the CO2 compensation point, 02 uptake equaled 02 production over a wide range of 02 concentrations. 02 uptake increased with light intensity and 02 concentration. At low light intensities, 02 uptake was suppressed by increased CO2 concentrations so that 02 uptake at 1,000 microliters per liter CO2 was 28 to 35% of the uptake at the CO2 compensation point. At high light intensities, 02 uptake was stimulated by low concentrations of CO2 and suppressed by higher concentrations of C02. 02 uptake at high light intensity and 1000 microliters per liter CO2 was 75% or more of the rate of 02 uptake at the compensation point. The response of 02 uptake to light intensity extrapolated to zero in darkness, suggesting that 02 uptake via dark respiration may be suppressed in the light. The response of 02 uptake to 02 concentration saturated at about 30% 02 in high light and at a lower 02 concentration in low light. 02 uptake was also observed with the C4 plant Amaranthus edulis, the rate of uptake at the CO2 compensation point was 20% of that observed at the same light intensity with the C3 species, and this rate was not influenced by the CO2 concentration. The results are discussed and interpreted in terms of the ribulose-1,5-bisphosphate oxygenase reaction, the associated metabolism of the photorespiratory pathway, and direct photosynthetic reduction of 02.Both 02 evolution and 02 uptake take place in leaves of C3 and C4 plants in the light (4,8,17,21,23,24,27,28). 02 evolution is derived entirely from the water-splitting reaction of PSII, but three principal 02 uptake processes are presently recognized. These are: the oxygenase reaction of ribulose bisP carboxylase-oxygenase and the associated metabolism of P-glycolate (2,4,5,18,20) Norway) was injected into the system. The system was closed and the gas was circulated over the leaf with a metal bellows pump. Mass 32, mass 36, and mass 40 were monitored continuously with a GD 150/4 mass spectrometer.02 uptake and 02 evolution were calculated using the methods previously described (25,27). CO2 concentration was measured with an IRGA analyzer (UNOR-2, Maihak, Hamburg, Germany) included in the gas circuit, and CO2 concentration during illumination could be controlled by varying the pressure of CO2 on a capillary that bled pure CO2 into the closed system. CO2 uptake, at constant CO2 concentration in the system, was calculated from the rate of CO2 addition. Each measurement was averaged over an 8-to 10-min period of gas exchange after the rate of CO2 uptake had reached a steady rate at each CO2 concentration. The total gas pressure in the small system increa...

Evidence for Cyclic Photophosphorylation during 14CO2 Fixation in Intact Chloroplasts

“…The evidence for the involvement of pseudocyclic electron transport in photosynthesis is based mainly on the observation of high rates of 02 uptake measured during photosynthesis at saturating CO2 in chloroplasts, cells, and leaves (6,(8)(9)(10). It is generally assumed that most of this 02 uptake is Fd-dependent and linked to ATP synthesis.…”

“…High rates of 02 uptake have been measured in thylakoid preparations from spinach leaves in the presence of high concentrations of Fd (1; R. T. Furbank and M. R. Badger, unpublished), during photosynthesis in intact chloroplasts and cells (8,9), and in leaves of C3 plants (6,10). The values of 02 uptake measured in these studies are comparable to and, in several cases, exceeded the value (1 1.3% of total 02 evolution) required for the generation of all the extra ATP needed for CO2 fixation.…”

“…It is now widely accepted that such a stoichiometric balance of ATP/NADPH could not be achieved by linear electron transport from H20 to NADP+ alone (1 1). Assuming that the ATP/NADPH ratio generated via linear electron transport is 1.33, the extra ATP needed would presumably be derived from cyclic and/or pseudocyclic electron transport.High rates of 02 uptake have been measured in thylakoid preparations from spinach leaves in the presence of high concentrations of Fd (1; R. T. Furbank and M. R. Badger, unpublished), during photosynthesis in intact chloroplasts and cells (8,9), and in leaves of C3 plants (6,10). The values of 02 uptake measured in these studies are comparable to and, in several cases, exceeded the value (1 1.3% of total 02 evolution) required for the generation of all the extra ATP needed for CO2 fixation.…”

Tansley Review No. 112

“…This situation is analogous to the induction period of photosynthesis (Marsho et al, 1979 ;Foyer et al, 1992). Although it has frequently been considered that high light intensities promote higher rates of O # reduction (Canvin et al, 1980 ;Badger, 1985 ;Grace & Logan, 1996), it has also been suggested that O # reduction accounts for a greater proportion of electron flow at low light intensities (Heber et al, 1978). If electrons do leak to O # at a fixed proportion of overall electron transport rates, then absolute rates of O # reduction will obviously increase with light intensity but will not increase further at light intensities above those saturating for photosynthesis (see an analogous discussion of photorespiration in section V(3)).…”

“…In many cases, concentrations of CO # intended to eliminate photorespiration have probably not been sufficiently high, and it is likely that ongoing lightdependent O # uptake at these ' high ' CO # concentrations mainly reflects continuing photorespiration (Canvin et al, 1980 ;Osmond & Grace, 1995). A complementary approach has exploited transformed plants with greatly decreased Rubisco activities (Ruuska et al, 2000).…”