Spinach chloroplast chlorophyll fluorescence at 685 and 735 nm (F685 and F735) has been time-resolved with a low-jitter streak camera system. Measurements are reported largely for 77 K, using single 30-ps 532-nm excitation pulses with pulse fluences of 2 · 1012 to 2 · 1016 photons · cm-2. A slightly fluence-dependent delay (16 ± 3 ps) found for the rise of F735 relative to F685 is too small to correspond to transfer into the species emitting F735 from the species emitting F685. The rise of F735 is biphasic at lower intensities and monophasic at higher intensity. The delay in the rise of F685 is smaller than approx. 2 ps. The time-resolved F685 is fit with a three-component model in which energy is transferred from a large pool of antenna chlorophylls to a small pool closely connected to the reaction center, all exciton annihilation occurring in the small pool. The F735 biphasic rise and its sensitivity to excitation fluence is explained by a similar but independent model. Data at our lowest intensities are consistent with those obtained by a photon-counting method using very low intensity excitation.
All Science Journal Classification (ASJC) codes
- Cell Biology