Effect of Photon Fluence Rate on Oxygen Evolution and Uptake by Chlamydomonas reinhardtii Suspensions Grown in Ambient and CO₂-Enriched Air

Abstract

A closed system consisting of an assimilation chamber furnished with a membrane inlet from the liquid phase connected to a mass spectrometer was used to measure 02 evolution and uptake by Chiamydomonas reinhardtii cells grown in ambient (0.034% C02) or C02-enriched (5% C02) air. At pH = 6.9, 28°C and concentrations of dissolved inorganic carbon (DIC) saturating for photosynthesis, 02 uptake in the light (U.) equaled 02 production (E.) at the light compensation point (15 micromoles photons per square meter per second). E, and U. increased with increasing photon fluence rate (PFR) but were not rate saturated at 600 micromoles photons per square meter per second, while net 02 exchange reached a saturation level near 500 micromoles photons per square meter per second which was nearly the same for both, C0rgrown and air-grown cells.Comparison of the U./E. ratios between air-grown and C02-grown C.reinhardtii showed higher values for air-grown cells at light intensities higher than light compensation. For both, air-grown and C02-grown algae the rates of mitochondrial 02 uptake in the dark measured immediately before and 5 minutes after illumination were much lower than U, at PFR saturating for net photosynthesis. We conclude that noncyclic electron flow from water to NADP and pseudocyclic electron flow via photosystem I to 02 both significantly contribute to 02 exchange in the light. In contrast, mitochondrial respiration and photosynthetic carbon oxidation cycle are regarded as minor 02 consuming reactions in the light in both, air-grown and C02-grown cells. It is suggested that the "extra" 02 uptake by air-grown algae provides ATP required for the energy dependent CO2/HCO3-concentrating mechanism known to be present in these cells.

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

“…This CO,-concentrating mechanism has also been shown to occur in diatoms (Burns and Beardall 1987;Colman and Rotatore 1988). The significance of the Mehler reaction during steady state photosynthesis is much more controversial (Sueltemeyer et al 1986;Brechignac and Furbank 1987). Although it is well established that 0, photoreduction can occur in vitro, the role and magnitude of this process has yet to be fully elucidated in vivo.…”

“…The second is oxidation of NADH and FADH, via either the cytochrome or alternative electron transport chains of the mitochondrion, which results in 0, consumption and production of ATP. The nature of O2 consumption by photosynthesizing cells has been the subject of much debate (Hoch et al 1963;Sueltemeyer et al 1986;Brechignat and Furbank 1987). Biochemical evidence suggests that at least some TCA-cycle carbon flow is maintained in the light (e.g.…”

Active Transport of Inorganic Carbon Increases the Rate of O2 Photoreduction by the Cyanobacterium Synechococcus UTEX 625

“…It was postulated that the rapid photoreduction of 02 after a period of darkness served as a priming reaction for the photosynthetic apparatus (19 Unlike previous work with cyanobacteria (3,8,9,12), recent work by Sueltemeyer et al (23,24) with Chlamydomonas has demonstrated an increased rate of 02 uptake with increased DIC concentration. It was concluded that the increased rate of 02 uptake was due to enhanced photoreduction in a Mehler-type reaction, and that extra ATP needed for increased rates of DIC uptake was synthesized as a result (23,24).…”

“…Sueltemeyer et al (23,24) have recently demonstrated that the rate of 02 photoreduction in air-grown cells of Chlamydomonas, which have high rates of DIC transport, is considerably higher than in 5% CO2 grown cells which have much lower rates of DIC transport. It was postulated that the photoreduction of 02 was coupled to ATP synthesis needed for DIC transport (23,24). It (Fig.…”

Comparison of the Oxygen Exchange between Photosynthetic Cell Suspensions and Detached Leaves of Euphorbia characias L

“…Second, the direct photoreduction of oxygen at the PSI acceptor site (Mehlertype reaction) is closely coupled with the electron transport system (1 probably occurs in the mitochondrion (21). Because of uncertainties due to stomate controls of photosynthetic processes in whole plants or detached leaves, microalgae have often been used as model systems (2,21,25). The development of photosynthetic plant cell cultures in suspensions has provided a cellular material obtained directly from higher plants which is as convenient as microalgae for experimental research on cellular metabolism, because of their availability in liquid conditions.…”