title: Changes in Photosystem II fluorescence in Chlamydomonas reinhardtii exposed to increasing levels of irradiance in relationship to the photosynthetic response to light.
abstract: The effects of a 60 min exposure to photosynthetic photon flux densities ranging from 300 to 2200 μmol m(-2)s(-1) on the photosynthetic light response curve and on PS II heterogeneity as reflected in chlorophyll a fluorescence were investigated using the unicellular green alga Chlamydomonas reinhardtii. It was established that exposure to high light acts at three different regulatory or inhibitory levels; 1) regulation occurs from 300 to 780 μmol m(-2)s(-1) where total amount of PS II centers and the shape of the light response curve is not significantly changed, 2) a first photoinhibitory range above 780 up to 1600 μmol m(-2)s(-1) where a progressive inhibition of the quantum yield and the rate of bending (convexity) of the light response curve can be related to the loss of QB-reducing centers and 3) a second photoinhibitory range above 1600 μmol m(-2)s(-1) where the rate of light saturated photosynthesis also decreases and convexity reaches zero. This was related to a particularly large decrease in PS IIα centers and a large increase in spill-over in energy to PS I.
authors.affiliation: Department of Plant Physiology, University of Umeå, S-901 87, Umeå, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Falk
authors.forename: J W
authors.initials: JW
authors.lastname: Leverenz
authors.forename: G
authors.initials: G
authors.lastname: Samuelsson
authors.forename: G
authors.initials: G
authors.lastname: Oquist