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Title: EVIDENCE THAT CYTOCHROME B559 PROTECTS PHOTOSYSTEM II AGAINST PHOTOINHIBITION

Author
item POULSON, MARY - UNIV ILLINOIS, URBANA, IL
item SAMSON, GUY - UNIV ILLINOIS, URBANA, IL
item WHITMARSH, CLIFFORD

Submitted to: Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Crops can be damaged by excess light, leading to loss of photosynthetic capacity. In an earlier study we discovered a molecular switch that controls the rate of photodamage. Here we provided evidence that the molecular switch is a heme protein, known as cytochrome b559, that is found in all plants. We propose that Cyt b559LP acts as a safety valve, protecting against photodamage by deactivating a potentially damaging high energy state. Understanding the processes that protect from excess light opens the door for developing genetically engineered plants designed to perform well under a wide range of environmental conditions.

Technical Abstract: Light that exceeds the photosynthetic capacity of a plant can impair the ability of photosystem II to oxidize water. The light-induced inhibition is initiated by inopportune electron transport reactions that create damaging redox states. We have shown that light-induced damage to photosystem II can be controlled by a redox component within the reaction center. The rate of photoinhibition is slow when the redox component is oxidized, but increases more than 10-fold when the redox component is reduced. Here we provide evidence that the redox component is cytochrome b559, an intrinsic heme protein of the photosystem II reaction center. The results support a model in which the low potential form of cytochrome b559 protects photosystem II by deactivating a rarely formed, but hazardous redox state of photosystem II. Cytochrome b559 is proposed to deactivate this potentially lethal redox state by accepting electrons from reduced pheophytin.