Development of photosystem-II activity during irradiance of etiolated Helianthus (Asteraceae) seedlings |
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Authors: | Jefferson G Lebkuecher Kurt A Haldeman Christine E Harris Sonia L Holz Sary A Joudah Darcy A Minton |
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Institution: | 1. Department of Biology, Austin Peay State University, Clarksville, Tennessee 37044
Author for correspondence.;2. Department of Biology, Austin Peay State University, Clarksville, Tennessee 37044 |
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Abstract: | Light-induced development of photosystem (PS)-II activity was followed during irradiance of etiolated Helianthus annuus (sunflower) cotyledons using chlorophyll a fluorescence. Cotyledons from seedlings grown in continuous darkness for 6 d were exposed to 100 μmol photons·m?2·s?1 for time periods of 1, 3, 6, and 12 h. Associated with increased time of irradiance exposure were significant: (1) increases in concentration of PS II, (2) increases in quantum efficiency of PS II, (3) decreases in the ratio of PS-II quinoneB (QB)-nonreducing centers to total PS-II centers (PS-II QB-nonreducing centers + PS-II QB-reducing centers), and (4) decreases in the ratio of slow PS-II QB-reducing centers to total PS-II QB-reducing centers (fast PS-II QB-reducing centers + slow PS-II QB-reducing centers). The results support the hypotheses that development of PS II involves assembly of complexes which initially cannot reduce QB and that heterogeneous aspects of PS-II pools during chloroplast maturation may represent different developmental states. |
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Keywords: | Asteraceae chlorophyll a fluorescence etioplast Helianthus photosystem-II development photosystem-II heterogeneity quinoneB |
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