Kinetics of the flash-induced electrochromic absorbance change in the presence of background illumination. Turnover rate of the electron transport. I: Isolated intact chloroplasts

The authors investigated the flash-induced electrochromic absorbance change, Delta A sub(515), of isolated intact chloroplasts in continuous monochromatic background light of different intensities and wavelengths. The steady-state turnover time of electron transport was found to be around 100 msec and the slowest process could be assigned to a photosystem 1 driven cycle. In contrast to earlier observations, the slow rise ( similar to 10 msec) of Delta A sub(515) in untreated chloroplasts persists also at high-intensity background illumination exciting both photosystems. The proportion of the slow rise of Delta A sub(515) in nigericin-treated chloroplasts increases in the presence of background light. This result on the slow rise is discussed in terms of two different models existing in the literature.