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Development of photosystem-II activity during irradiance of etiolated Helianthus (Asteraceae) seedlings¹

Department of Biology, Austin Peay State University, Clarksville, Tennessee 37044

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 quinone_B (Q_B)-nonreducing centers to total PS-II centers (PS-II Q_B-nonreducing centers + PS-II Q_B-reducing centers), and (4) decreases in the ratio of slow PS-II Q_B-reducing centers to total PS-II Q_B-reducing centers (fast PS-II Q_B-reducing centers + slow PS-II Q_B-reducing centers). The results support the hypotheses that development of PS II involves assembly of complexes which initially cannot reduce Q_B and that heterogeneous aspects of PS-II pools during chloroplast maturation may represent different developmental states.

Key Words: Asteraceae • chlorophyll a fluorescence; etioplast • Helianthus • photosystem-II development; photosystem-II heterogeneity; quinone_B

This article has been cited by other articles:

				K. Solymosi, B. Vitanyi, E. Hideg, and B. Boddi Etiolation Symptoms in Sunflower (Helianthus annuus) Cotyledons Partially Covered by the Pericarp of the Achene Ann. Bot., May 1, 2007; 99(5): 857 - 867. [Abstract] [Full Text] [PDF]