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Photosystem II Cyclic Heterogeneity and Photoactivation in the Diazotrophic, Unicellular Cyanobacterium Cyanothece Species ATCC 511421

Pascal C. Meunier, Milagros S. Colón-López, and Louis A. Sherman*

Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907

The unicellular, diazotrophic cyanobacterium Cyanothece sp. ATCC 51142 demonstrated important modifications to photosystem II (PSII) centers when grown under light/dark N2-fixing conditions. The properties of PSII were studied throughout the diurnal cycle using O2-flash-yield and pulse-amplitude-modulated fluorescence techniques. Nonphotochemical quenching (qN) of PSII increased during N2 fixation and persisted after treatments known to induce transitions to state 1. The qN was high in cells grown in the dark, and then disappeared progressively during the first 4 h of light growth. The photoactivation probability, epsilon , demonstrated interesting oscillations, with peaks near 3 h of darkness and 4 and 10 h of light. Experiments and calculations of the S-state distribution indicated that PSII displays a high level of heterogeneity, especially as the cells prepare for N2 fixation. We conclude that the oxidizing side of PSII is strongly affected during the period before and after the peak of nitrogenase activity; changes include a lowered capacity for O2 evolution, altered dark stability of PSII centers, and substantial changes in qN.

1   This work was supported by grants from the U.S. Department of Energy (no. DE-FG02-89ER14028A) and the U.S. Department of Agriculture (no. 93-37306-9238) to L.A.S.
*   Corresponding author; e-mail lsherman{at}bilbo.bio.purdue.edu; fax 1-765-496-1495.

Plant Physiol. (1998) 116: 1551-1562
Copyright Clearance Center:   0032-0889/98/116/1551/12
© 1998 American Society of Plant Physiologists




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[Abstract] [Full Text] [PDF]


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