title: Light- and CO2-saturated photosynthesis: enhancement by oxygen.
abstract: Oxygen may enhance CO2-saturated photosynthesis in intact leaves, which display the Warburg effect when illuminated at the current atmospheric level of CO2 and O2, of about 350 microl l(-1) and 21%, respectively. The magnitude of the stimulation depends on irradiance. The K(M)(O2) of the stimulation is 128 microM (10.6% O2). Maximum enhancement in wheat leaves is 6.1 and 5.3 micromol m(-2) s(-1 )under 27.9 and 18.7 mW cm(-2), respectively, corresponding to a 25-30% increase in the ribulose 1,5-bisphosphate (RuBP) turnover rate if compared with O2-free ambient gas phase. The stimulation appears in 5-10 s after a sharp increase in O2. In response to a decrease in O2, the new stabilized rate is reached in 5-7 min. The stimulation does not involve any increase in the activity of Rubisco. The effect correlates with increased concentration of RuBP. Oxygen enhances CO2-saturated photosynthesis by acting as a terminal electron acceptor in the photosynthetic electron transport. The magnitude of the effect may be adopted as an index of the pseudocyclic photophosphorylation in vivo.
authors.affiliation: Division of Plant Physiology, Institute of Agriculture and Environment, Estonian Agricultural University, 76902 Harku, Estonia. juta@ebi.ee
authors.forename: Juta
authors.initials: J
authors.lastname: Viil
authors.forename: Hiie
authors.initials: H
authors.lastname: Ivanova
authors.forename: Tiit
authors.initials: T
authors.lastname: Pärnik
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology*; D008027:Light; D010100:Oxygen / Q000378:metabolism / Q000494:pharmacology*; D010788:Photosynthesis / Q000187:drug effects* / Q000528:radiation effects*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D010943:Plantago / Q000378:metabolism; D014908:Triticum / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen