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- FALK, S, et al.
(författare)
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CHANGES IN PHOTOSYSTEM-II FLUORESCENCE IN CHLAMYDOMONAS-REINHARDTII EXPOSED TO INCREASING LEVELS OF IRRADIANCE IN RELATIONSHIP TO THE PHOTOSYNTHETIC RESPONSE TO LIGHT
- 1992
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Ingår i: Photosynthesis Research. - 0166-8595 .- 1573-5079. ; 31:1, s. 31-40
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- LEVERENZ, JW, et al.
(författare)
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PHOTOSYNTHESIS AND PHOTOINHIBITION IN LEAVES OF CHLOROPHYLL-B-LESS BARLEY IN RELATION TO ABSORBED LIGHT
- 1992
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 85:3, s. 495-502
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Tidskriftsartikel (refereegranskat)abstract
- The response of photosynthesis to absorbed light by intact leaves of wild-type (Hordeum vulgare L. cv. Gunilla) and chlorophyll b-less barley (H. vulgare L. cv. Dornaria, chlorina-f2(2800)) was measured in a light integrating sphere. Up to the section where the light response curve bends most sharply the responses of the b-less and wild-type barley were similar but not identical. Average quantum yield and convexity for the mutant light response curves were 0.89 and 0.90, respectively times those of the wild-type barley. The maximum quantum yield for PSII photochemistry was also 10% lower as indicated by fluorescence induction kinetics (F(v)/F(m)). Just above the region where the light curve bends most sharply, photosynthesis decreased with time in thc mutant but not in the wild-type barley. This decrease was associated with a decrease in F(v)/F(m) indicating photoinhibition of PSII. This photoinhibition occurred in the same region of the light response curve where zeaxanthin formation occurs. Zeaxanthin formation occurred in both the chlorophyll b-less and wild-type leaves. However, the epoxidation state was lower in the mutant than in the wild-type barley. The results indicate that chlorophyll b-less mutants will have reduced photosynthetic production as a result of an increased sensitivity to photoinhibition and possibly a lowered quantum yield and convexity in the absence of photoinhibition.
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