CHANGES IN PHOTOSYSTEM-II FLUORESCENCE IN CHLAMYDOMONAS-REINHARDTII EXPOSED TO INCREASING LEVELS OF IRRADIANCE IN RELATIONSHIP TO THE PHOTOSYNTHETIC RESPONSE TO LIGHT

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The effects of a 60 min exposure to photosynthetic photon flux densities ranging from 300 to 2200-mu-mol 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-mu-mol 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-mu-mol 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 Q(B)-reducing centers and 3) a second photoinhibitory range above 1600-mu-mol 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 II(alpha) centers and a large increase in spill-over in energy to PS I.

LEVERENZ, JW (författare)
Samuelsson, Göran,1951-Umeå universitet,Institutionen för fysiologisk botanik,Umeå Plant Science Centre (UPSC)(Swepub:umu)gosa0002 (författare)
Oquist, Gunnar,1941-Umeå universitet,Institutionen för fysiologisk botanik,Umeå Plant Science Centre (UPSC)(Swepub:umu)guoq0001 (författare)
Umeå universitetInstitutionen för fysiologisk botanik (creator_code:org_t)

Av författaren/redakt...: FALK, S; LEVERENZ, JW; Samuelsson, Göra ...; Oquist, Gunnar, ...

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