Search results for "photoinhibition"
showing 8 items of 18 documents
The Effect of Temperature and Radical Protection on the Photoinhibition of Spinach Thylakoids
1992
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 …
Studies on the mechanism of photosystem II photoinhibition I. A two-step degradation of D1-protein
1990
The role of D1-protein in photoinhibition was examined. Photoinhibition of spinach thylakoids at 20°C caused considerable degradation of D1-protein and a parallel loss of variable fluorescence, QB-independent electron flow and QB-dependent electron flow. The breakdown of D1-protein as well as the loss of variable fluorescence and QB-independent electron flow were largely prevented when thylakoids were photoinhibited at 0°C. The QB-dependent electron flow markedly decreased under the same conditions. This inactivation may represent the primary event in photoinhibition and could be the result of some modification at the QB-site of D1-protein. Evidence for this comes from fluorescence relaxati…
Studies on the mechanism of photosystem II photoinhibition II. The involvement of toxic oxygen species.
1990
In a previous paper it was shown that photoinhibition of reaction centre II of spinach thylakoids was predominantly caused by the degradation of D1-protein. An initial inactivation step at the QB-site was distinguished from its breakdown. The present paper deals with the question as to whether this loss of QB-function is caused by oxygen radical attack. For this purpose the photoinhibition of thylakoids was induced at 20°C in the presence of either superoxide dismutase and catalase or the antioxidants glutathione and ascorbic acid. This resulted in comparable though not total protection of D1-protein, photochemistry and fluorescence from photoinhibition. The combined action of both the enzy…
Changes of the Quantum Yield of Oxygen Evolution and the Electron Transport Capacity of Isolated Spinach Thylakoids during Photoinhibition
1992
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…
Physiological,anatomical and biomass partitioning responses to ozone in the Mediterranean endemic plant Lamottea dianae
2011
Ozone effects on the perennial forb Lamottea dianae were studied in an open-top chamber experiment. Ozone was found to induce reductions in CO 2 assimilation and water use efficiency in the leaves of this species. These reductions were mainly related to a decline in the in vivo CO 2 fixation capacity of Rubisco (V c,max), rather than to stomatal limitations or photoinhibitory damage (F v:F m). In addition to chloroplast degeneration, other observed effects were callose accumulation, formation of pectinaceous wart-like cell wall exudates and phloem alterations. Moreover, ozone exposure significantly reduced root dry biomass. The possible relevance of these adverse effects for Mediterranean f…
The Mechanism of Photoinhibition of Spinach Thylakoids
1990
There is conflicting evidence as to wether D1-protein is the primary target of photoinhibition [1] or P680, the reaction centre of photo-system II [2]. The present paper desribes photoinhibition within a two step process consisting of an oxygen radical induced inactivation at the QB-site followed by damage to reaction centre II through the degradation of the D1-protein.
Multiple Short Term Effects of UV-B Radiation on the Diatom Phaeodactylum Tricornutum
1998
Increases in UV-B irradiance lead to many specific damaging effects upon the plants including damage of the thylakoid membrane, partial inhibition of PS II, decrease of chloroplast ATPase activity, loss of enzyme activities in the calvin cycle and alterations in pigment synthesis (1). Under natural conditions enhanced UV-B light is always accompanied by high intensities of photosynthetic active radiation (PAR). Damaging effects due to photoinhibitory PAR and UV-B light which lead to several oxygen radical species (2) could be reduced by photoprotection mechanisms. One of these protection mechanisms is the xanthophyll cycle. In higher plants and green algae violaxanthin is converted to zeaxa…
Diurnal Cycle Relationships between Passive Fluorescence, PRI and NPQ of Vegetation in a Controlled Stress Experiment
2017
In order to estimate vegetation photosynthesis from remote sensing observations; some critical parameters need to be quantified. From all absorbed light; the plant needs to release any excess that is not used for photosynthesis; by non-photochemical quenching; by fluorescence emission and unregulated thermal dissipation. Non-photochemical quenching (NPQ) processes are controlled photoprotective mechanisms which; once activated; strongly control the dynamics of photochemical efficiency. With illumination conditions increasing and decreasing during a diurnal cycle; photoprotection mechanisms needs to change accordingly. The goal of this work is to quantify dynamic NPQ; measured from active fl…