Simultaneous analysis of variable and delayed chlorophyll fluorescence during induction period in photosynthetic apparatus

Abstract

Phosphoroscope equipment (giving light/dark circles of about 100 Hz) for simultaneous registration of prompt and sub- and millisecond delayed chlorophyll fluorescence (PF and DF, respectively) have been employed to analyze the changes in state of photosynthetic apparatus by illumination during induction period. The DF induction curve can be described by 6 differently pronounced maximums by induction time, denoted as I1 ÷ I6. The I1 and I2 maximums coincide with the moments of maximal fluorescence rise (inflexions) in the J-I and I-P phases of the PF kinetics. The DF decline after I2 (called D2) is observed at the time when PF reached maxima (Fp or Fm). During the induction period at each moment the DF the decay kinetics (within 0.5 ÷ 5.5 ms) are available. During fluorescence rise (up to about 1 s) the DF value can be presented as a superposition of components with lifetimes t 1 = 0.5 ÷ 0.7 ms and t 2 = 1.5 ÷ 3.5 ms, correspondingly. Later the contribution of a slow component with t 3 = 15 ¸ 20 ms becomes predominant. During the first second of induction t 2 rises from 1.5 to 3.5 ms. We assume, that sub- and millisecond components of DF arrive from radiative recombination reactions in PS2 reaction centers in states Z+P680QA¿QB¿ and Z+P680QA¿QB=, respectively. The I1 and I2 of DF induction kinetics reflect the dynamics of above mentioned redox states. The relative amplitude of I1 and I2 is determined by electron flows toward and from QAQB acceptor complexes. Acknowledgments: We thank the Swiss National Scientific Fund for financial support (SCOPES 2000 _ 2003 grant _ 7BUPJ062408.00/1). Detelin Stefanov is grateful for personal finance by Japan Society for the Promotion of Science (JSPS).