0000000000459756
AUTHOR
Birgit Böthin
The Effect of Temperature and Radical Protection on the Photoinhibition of Spinach Thylakoids
Photoinhibition of spinach thylakoids was studied by examination the inactivation of different parts of the electron transport chain, the decline of the variable fluorescence and the loss of atrazine binding sites. The results obtained after photoinhibition at 20° C and 0° C revealed an inactivation at the QB-site of the D1-protein as the first event in the course of photoinhibition. The natural antioxidants glutathione and ascorbate as well as the enzymes SOD and catalase diminished photoinhibition to similar extents. Further protection was achieved through combination of both radical defense systems. In addition to the radical scavenging properties glutathione and ascorbate have reducing …
Changes of the Quantum Yield of Oxygen Evolution and the Electron Transport Capacity of Isolated Spinach Thylakoids during Photoinhibition
Summary Isolated spinach thylakoids can be protected from photoinhibitory loss of electron transport capacity by the radical defense system composed of the enzymes SOD and catalase, as well as the antioxidants glutathione and ascorbate. With these compounds present at saturating concentrations, thylakoids not only retain a high photochemical capacity but also do not suffer D1-protein degradation during photoinhibition. However, a strong decrease in the quantum yield of oxygen evolution, Φ O 2 , occurs with the same thylakoids. These results support the view that the photochemical capacity and the quantum yield of oxygen evolution decline due to different mechanisms during photoinhibition. T…
Zeaxanthin Dependent and Zeaxanthin Independent Changes in Nonphotochemical Energy Dissipation
Summary The influence of zeaxanthin on high-energy-state quenching (qE) of room temperature chlorophyll fluorescence and on the quantum yield of oxygen evolution(ФO2) has been studied with isolated spinach thylakoids. A set of three different pretreatments was tested which all led to thylakoids with high contents of zeaxanthin. Depending on the presence of light the pretreatments differed strongly with respect to their effect on nonphotochemical fluorescence quenching. Independently from the extent of changes in nonphotochemical energy dissipation in the membrane energized state as reflected by nonphotochemical quenching the light pretreatments caused also changes in nonphotochemical energy…