We investigated the flash-induced electrochromic absorbance change, ΔA515, of isolated intact chloroplasts in continuous monochromatic background light of different intensities and wavelengths. From the variation of the amplitude of ΔA515 in background illumination 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. The change of ΔpH induced by nigericin, ATP, or ADP did not modify substantially the turnover time. In contrast to earlier observations the slow rise (∼10 msec) of ΔA515 in untreated chloroplasts persists also at high-intensity background illumination exciting both photosystems. The proportion of the slow rise of ΔA515 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.
ASJC Scopus subject areas
- Cell Biology