C. Geel et al., ESTIMATION OF OXYGEN EVOLUTION BY MARINE-PHYTOPLANKTON FROM MEASUREMENT OF THE EFFICIENCY OF PHOTOSYSTEM-II ELECTRON FLOW, Photosynthesis research, 51(1), 1997, pp. 61-70
The relation between photosynthetic oxygen evolution and Photosystem I
I electron transport was investigated for the marine algae Phaeodactyl
um tricornutum, Dunaliella tertiolecta, Tetraselmis sp., Isochrysis sp
, and Rhodomonas sp.. The rate of Photosystem II electron transport wa
s estimated from the incident photon flux density and the quantum effi
ciency of Photosystem II electron transport as determined by chlorophy
ll fluorescence, The relation between the estimated rate of Photosyste
m II electron transport and the rate of oxygen evolution was investiga
ted by varying the ambient light intensity. At limiting light intensit
ies a linear relation was found in all species. At intensities approac
hing light saturation, the relation was found to deviate from linearit
y, The slope of the line in the light-limited range is species depende
nt and related to differences in absorption cross-section of Photosyst
em II. The observed non-linearity at high irradiances is not caused by
photorespiration but probably by a Mehler-type of oxygen reduction. T
he relationship could be modelled by including a redox-state dependent
oxygen uptake, In the diatom Phaeodactylum tricornutum, the photochem
ical efficiency of dark adapted open Photosystem II centers was found
to be temperature-dependent with an optimum near 10 degrees C.