Non-photochemical quenching of chlorophyll fluorescence indicates the de-excitation of light-generated excited states in the chlorophyll associated with photosystem I1 (PSII). The principle process contributing to this quenching is dependent on the formation of the thylakoid proton gradient and is an important mechanism for protecting PSII from photodamage. Evidence points to the importance of the light-harvesting chlorophyll proteins as the site of dissipation of energy, and suggests that the structure and function of these proteins are regulated by protonation and the ratio of zeaxanthin to violaxanthin. The minor light-harvesting proteins may have a particularly important role as the primary sites of proton binding and because of their enrichment in xanthophyll cycle carotenoids. The dynamic nature of the light-harvesting system is an important part of the process by which plants are able to adapt to different light environments.
The behaviour of t h e crystal structure of the YBCO epitaxial films with enlarged c-axis parameter has been studied. The c-axis expansion effect is shown to be induced by low oxygen partial pressure during the film deposition. This effect cannot be explained only by oxTgen deficit in the C u 4 chains or (Y. Ea) cation disorder. A bridging oxygen disorder model shows qualitative agreement with experimental x-ray diffraction spectra. Thermodynamic analysis of the formation of oxygen vacancies shows the high theoretical density of the bridging oxygen vacancies at the film synthesis temperatures.
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