The kinetics of light-induced changes of C-550, cytochrome b559 and fluorescence yield in chloroplasts at low temperature |
| |
Authors: | Warren L. Butler Jan W.M. Visser Hugo L. Simons |
| |
Affiliation: | Biophysical Laboratory, State University, Schelpenkade 14 A, Leiden The Netherlands |
| |
Abstract: | The kinetics of the photoreduction of C-550, the photooxidation of cytochrome b559 and the fluorescence yield changes during irradiation of chloroplasts at ?196 °C were measured and compared. The photoreduction of C-550 proceeded more rapidly than the photooxidation of cytochrome b559 and the fluorescence yield increase followed the cytochrome b559 oxidation. These results suggest that fluorescence yield under these conditions indicates the dark reduction of the primary electron donor to Photosystem II, P680+, by cytochrome b559 rather than the photoreduction of the primary electron acceptor.The photoreduction of C-550 showed little if any temperature dependence over the range of ?196 to ?100 °C. The amount of cytochrome b559 photooxidized was sensitive to temperature decreasing from the maximal change at temperatures between ?196 to ?160 °C to no change at ?100 °C. To the extent that the reaction occurred at temperatures between ?160 and ?100 °C the rate was largely independent of temperature. The rate of the fluorescence increase was dependent on temperature over this range being 3–4 times more rapid at ?100 than at ?160 °C. At ?100 °C the light-induced fluorescence increase and the photoreduction of C-550 show similar kinetics. The temperature dependence of the fluorescence induction curve is attributed to the temperature dependence of the dark reduction of P680+.The intensity dependence of the photoreduction of C-550 and of the photooxidation of cytochrome b559 are linear at low intensities (below 200 μW/cm2) but fall off at higher intensities. The failure of reciprocity in the photoreduction of C-550 at the higher intensities is not explained by the simple model proposed for the Photosystem II reaction centers. |
| |
Keywords: | DCMU 3-(3 4-dichlorophenyl)-1 1-dimethylurea |
本文献已被 ScienceDirect 等数据库收录! |