title: Post-illumination transient O2-uptake is driven by photorespiration in tobacco leaves.
abstract: This study aims to elucidate the molecular mechanism for the transient increase in the O2-uptake rate in tobacco (Nicotiana tabacum cv Xanthi) leaves after turning off actinic lights (ALs). The photosynthetic O2evolution rate reaches a maximum shortly after the onset of illumination with ALs and then decreases to zero in atmospheric CO2/O2conditions. After turning off the ALs, tobacco leaves show a transient increase in the O2-uptake rate, the post-illumination transient O2-uptake, and thereafter, the O2-uptake rate decreases to the level of the dark-respiration rate. Photosynthetic linear electron flow, evaluated as the quantum yield of photosystem II [Y(II)], maintained a steady-state value distinct from the photosynthetic O2-evolution rate. In high-[CO2] conditions, the photosynthetic O2-evolution rate and Y(II) showed a parallel behavior, and the post-illumination transient O2-uptake was suppressed. On the other hand, in maize leaves (a C4 plant), even in atmospheric CO2/O2conditions, Y(II) paralleled the photosynthetic O2-evolution rate and the post-illumination transient O2-uptake was suppressed. Hypothesizing that the post-illumination transient O2-uptake is driven by C3 plant photorespiration in tobacco leaves, we calculated both the ribulose 1,5-bisphosphate carboxylase- and oxygenase-rates (Vc and Vo) from photosynthetic O2-evolution and the post-illumination transient O2-uptake rates. These values corresponded to those estimated from simultaneous chlorophyll fluorescence/O2-exchange analysis. Furthermore, the H+-consumption rate for ATP synthesis in both photosynthesis and photorespiration, calculated from both Vc and Vo that were estimated from chlorophyll fluorescence/CO2-exchange analysis, showed a positive linear relationship with the dissipation rate of the electrochromic shift signal. Thus, these findings support our hypothesis.
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
authors.forename: Takehiro
authors.initials: T
authors.lastname: Sejima
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
authors.forename: Hitomi
authors.initials: H
authors.lastname: Hanawa
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
authors.forename: Ginga
authors.initials: G
authors.lastname: Shimakawa
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Takagi
authors.affiliation: Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Suzuki
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fukayama
authors.affiliation: Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan.
authors.forename: Amane
authors.initials: A
authors.lastname: Makino
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, Kobe, Japan.
authors.forename: Chikahiro
authors.initials: C
authors.lastname: Miyake