Effects of Light Stress on Redox Potential Forms of Cyt b-559 in Photosystem II Membranes Depleted of Water-Oxidizing Complex : MEMBRANES AND BIOENERGETICS

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Effects of photoinhibition on the redox properties of Cyt b-559 were studied with NH_2OH-treated PSII membranes, which are depleted of the water-oxidizing complex. The membranes contained three redox forms (HP-, IP- and LP-forms) of Cyt b-559, with E_m values of ^+435, ^+237 and ^+45 mV, respectively. A novel intermediate-potential form of Cyt b-559 was generated during photoinhibition on the donor side of PSII: photoinhibitory illumination (7,000 μE m^<-2>s^<-1>) for 1 min induced a 30% decrease in the level of the HP-form, with concomitant generation of the intermediate-potential (IP'-) form whose E_m value was about ^+350 mV. Prolonged illumination (10 min) resulted in complete loss of the HP-form and an apparent increase in the level of the IP-form. After further photoinhibitory treatment (60 min), complete loss of the IP'-form was observed and levels of the IP- and LP-forms each increased to about 50% of the total amount of Cyt b-559. Kinetic analysis of these data led to the conclusion that the HP-form is converted to the LP-form via two intermediate-potential forms (IP' and IP), and that IP'-form appears only at the early phase of photoinhibition.
日本植物生理学会の論文