Measurement of Photorespiration in Algae

Abstract

The rates of true and apparent photosynthesis of two unicellular green algae, one diatom and four blue-green algae were measured in buffer at pH 8.0 at subsaturating concentrations of dissolved inorganic carbon (13-27 micromolar). Initial rates of depletion from the medium of inorganic carbon and "C activity caused by the algae in a closed system were measured by gas chromatography and by liquid scintillation couating, respectively. The rate of photorespiration was calculated as the difference between the rates of apparent and true photosynthesis. The three eucaryotic algae and two blue-green algae had photorespiratory rates of 10 to 28% that of tre photosynthesis at air levels of 02. Reduction of the 02 level to 2% caused a 52 to 91% reduction in photorespiratory rate. Two other blue-green algae displayed low photorespiratory rates, 2.4 to 6.2% that oftrue photosynthesis at air levels of 02, and reduction of the 02 concentration had no effect on these rates. (668) were obtained from the culture collection ofalgae at the University of Texas, Austin (culture collection numbers in parentheses). Phormidium molle was a gift from Dr. S. R. Brown, Queen's University, Kingston, Ontario.Algae were grown in batch culture without the addition of supplementary CO2 as previously described (4). Cells were harvested by centrifugation at 3,000g for 10 min, and resuspended in 50 mM K-phosphate (pH 7.8-8.0) which had been previously flushed with either 'COrfree' N2 or air to establish low or airsaturated levels of dissolved 02. The algal suspension was contained in an illuminated, water-jacketed cylindrical glass vessel sealed from the air with a layer of mineral oil as previously described (7) and the algae maintained in suspension by stirring with a magnetic stirrer. Light intensity for photorespiration measurements was 4 x 105, w cm-2. All assays were performed at the temperatures used for growth of the algae. NaH 4CO3 (2)(3)(4)(5)(6)(7)(8)(9)(10)iCi) was added to the cells and a 3 to 5 ml sample withdrawn in a syringe to determine the initial total DIC and 4C activity. Following separation of the cells by membrane filtration(4), 0.5 ml cellfree medium was added to 0.5 ml ethanolamine in a scintillation vial, and 0.25 to 0.5 ml injected directly into a modified gas chromatograph to determine total DIC (4). The depletion of DIC and radioactivity in the medium was similarly determined at timed intervals, after the lights had been turned on. To monitor release of acid-stable "4C-labeled compounds during photosynthesis, 0.5 ml cell-free medium was added to 0.5 ml 50%o glacial acetic acid and gently flushed with CO2 gas for 20 to 30 min prior to addition of 10 ml Bray's cocktail for liquid scintillation counting.Rates of true photosynthesis, apparent photosynthesis and photorespiration were calculated from the rates of 14C uptake and DIC uptake in the light following the method of Hew et al. (15).The rate of TPS was calculated from the initial rate of depletion of 14C activity in the medium over the initial 2 to 4 min ...

Respiratory losses in the light in a marine diatom: Measurements by short‐term mass spectrometry

“…The apparent absence of photorespiratory gas exchange in T. weisflogii is typical of algae in general (Birmingham et al 1982). It is thought to be due to the ability of these organisms to actively accumulate inorganic carbon, elevating internal CO2 relative to O2 and thereby suppressing the oxygenase activity of Rubisco and hence photorespiration (Badger et al 1978).…”

Ecosystem metabolism in salt marsh tidal creeks and ponds : applying triple oxygen isotopes and other gas tracers to novel environments

“…Photorespiration can be a significant sink of O2 for some algal and seagrass species (Birmingham et al 1982, Buapet et al 2013. However, the CO2 in the pond is probably well in excess of atmospheric abundance (CO2 estimated from DIC and assumed pH near 8.0(NBS) in CO2Sys v2.1), so it seems unlikely that photorespiration is a major sink in this environment compared to some of the other likely O2 consuming processes.…”

“…While this technique is broadly applicable and informative, it may be biased by methodological or environmental factors (like any technique for measuring primary production, see Chapter 1); an important drawback is that oxygen concentrations may not adequately reflect the net effect of diverse metabolic processes in an environment, such as additional biological sinks of O2 that are decoupled from organic matter production or respiration, or anoxygenic primary production in sediments. Such processes occur in many shallow aquatic environments (Birmingham et al 1982, Pinckney and Paerl 1997.…”

Physiological‐environmental Interactions in Lichens

“…In terrestial plants, where COj exchange is gaseous, COm easurement by infrared gas analyser (IRGA) systems provides an accurate means of evaluating carbon fluxes. In addition, placement of surface cyanophyte mats in incubation cuvettes does not entail physiological disturbance of experimental material comparable to that involved in the suspension of aquatic species in gaseous airstreams, or the adjustment of aquatic media to pH 4 to S so that HCO^ê xchange is minimized (Birmingham, Coleman and Colman, 1982). Photorespiratory patterns have been examined indirectly by measurement of CO^ compensa-tion points in a range of lichenized blue-green algae (Snelgar and Green 1981).…”