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

Abstract

We investigated the flash-induced electrochromic absorbance change, ΔA ₅₁₅, of isolated intact chloroplasts in continuous monochromatic background light of different intensities and wavelengths. From the variation of the amplitude of ΔA ₅₁₅ 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 ΔA ₅₁₅ in untreated chloroplasts persists also at high-intensity background illumination exciting both photosystems. The proportion of the slow rise of ΔA 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.