Picosecond fluorescence study of photosynthetic mutants of Chlamydomonas reinhardii: origin of the fluorescence decay kinetics of chloroplasts.

The fluorescence decay kinetics of photosynthetic mutants of Chlamydornonas reinhardii which lack photosystem 11 (PS 11), photosystem I (PS I), and both PS I1 and PS I have been measured. The PS I1 mutant strain 8-36C exhibits fluorescence decay lifetime components of 53, 424 and 2197 ps. The fluorescence decay of a PS I mutant strain 12-7 contains two major fluorescence decay components with lifetimes of 152 and 424 ps. The fluorescence decay of mutant strain C2, which lacks both PS I1 and PS I, is nearly single exponential with a lifetime of 2561 k 222 ps. In simulations in which it is assumed that wild-type decays are a simple sum of the major decay components of the isolated parts of the photosynthetic unit as measured in the mutants, curves are obtained that fit the wild-type C. reinhardii fluorescence decay data when the absorption cross-sections of PS I1 and PS I are weighted approximately equally. The 89 ps lifetime component in the wild-type is an average of 53 and 152 ps components arising from excitation transfer to and trapping in PS I and PS 11. The single step transfer time in PS I is estimated to be between 100 and 700 fs depending on assumptions about array size. We find that between two and four visits to the PS I reaction center are required before final trapping. . .