A selective effect of Mg2+ on the photochemistry at one type of reaction center in photosystem II of chloroplasts

  • Melis A
  • Homann P
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The area growth over the seemingly exponential fluorescence rise curve of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea-poisoned, envelope-free chloroplasts suspended in media devoid of Mg2+ is biphasic. Its kinetics can be described as the sum of two independently occurring first order processes which are attributed to two different types of photochemical centers in unicentral photosystem II units. An addition of Mg2+ changes the kinetic pattern of the photochemistry at one type of centers to nonfirst order, but does not affect the kinetics at the other type. This differential effect of Mg2+ suggests that certain photochemical centers and their light harvesting pigments may become integrated in larger, multicentral units under the influence of Mg2+, or become more tightly coupled to adjacent light harvesting pigment beds.

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  • Anastasios Melis

  • Peter H Homann

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