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    STUDIA BIOLOGIA - Issue no. 2 / 2008  
         
  Article:   THE PHOTOCHEMICAL ACTIVITY OF PS II AND PS I PHOTOSYSTEMS IN GREEN ALGA MOUGEOTIA SP. IN THE PRESENCE OF ASCORBATE AND HYDROGEN PEROXIDE, IN STATE 2 TRANSITION.

Authors:  CRISTIAN COMAN, VICTOR BERCEA. 		 
       
         
  Abstract:  The photochemical activity in the photosystems as a response to the photoinhibition inducement through intense light in the presence of different concentrations of enzymatic substrate (ascorbate) and under the intensification of the oxidative factor (H2O2) in state 2 transition was studied. F0 had risen to 20 mM sodium ascorbate and decreased in the presence of H2O2. DCMU led to an increase of F0 which reflects the reduction of the opened reaction centers. Fm has been stimulated under actinic light at 20 mM and 30 mM ascorbate and in red light. The Fm diminish occurred in H2O2. Fv decreased in the presence of 10 mM ascorbate and H2O2. High ascorbate concentration led to an increase of Fv proportionally with the exposure period. Fv/Fm as well as the yield have decreased, more pronounced in the presence of H2O2. The photochemical efficiency remission as well as Fm’s point out the photoinhibition installment in the photosystems. qp has increased so that the reduction state in the PS II is high leading to an increase of the excitation pressure. The excitation energy dissipation rate has risen also in the photosystems’ antenna. Generally, the cytochrome b6f has been in a reduced state. In state 2, the reduction of the cytochrome b6f gets dominant by exposure to light which induces a specific activity in PS I therefore the quantity of the electrons which flow towards PS I has also increased.

KEYWORDS: chlorophyll fluorescence, down regulation, photoinhibition, plastoquinone, quantum yield 		 
         
     
         
         
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