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    STUDIA BIOLOGIA - Issue no. 1 / 2013  
         
  Article:   THE EFFECT OF DIFFERENT LIGHT INTENSITIES ON PHOTOCHEMICAL ACTIVITY IN MICROCYSTIS AERUGINOSA AICB 702 STRAIN (CYANOPHYTA).

Authors:  ADRIANA HEGEDŰS (BICA), VICTOR BERCEA, BOGDAN DRUGĂ, COSMIN IONEL SICORA.
 
       
         
  Abstract:  VIEW PDF: THE EFFECT OF DIFFERENT LIGHT INTENSITIES ON PHOTOCHEMICAL ACTIVITY IN MICROCYSTIS AERUGINOSA AICB 702 STRAIN (CYANOPHYTA)

Microcystis aeruginosa AICB 702 was grown at room temperature, on GZ medium, in air-lift conditions, using a medium light intensity of 260 µmol. m-2.s-1. The exponential-phase cells were exposed to 800, 1500 and 2100 µmol. m-2.s-1 light intensities and the fluorescence measurements were performed after 15, 30, 45, 60, 75, 90, 105 and 120 minutes of light exposure. Dark-adapted probes were analyzed after 120 minutes recovery period. The oxidation state of primary acceptor and the fraction of the reaction centers are reduced (damaged), the photochemical process and the light harvesting are slightly inhibited when an 800 µmol. m-2.s-1 light intensity is used. Also, the reduction of the primary acceptor and the reaction centers closure were maximal. The Fv/Fm and Y(II) quantum yield were inhibited. The Fv/Fm values registered toward the end of the experiment represented 46.5% of the theoretical value, which also indicates the ratio of the PS II reaction centers that were photoinhibited. The non-regulated energy dissipation increased, and the high values of qP and qL coefficients showed an enhanced photochemical process with a low fluorescence emission. Increased F0 and Fm and Fv decreased when 1500 μmol.m-2.s-1 was used. The Fv/Fm and Y(II) diminished and the non-regulated energy dissipation increased. When a light intensity of 2100 μmol.m-2.s-1was used, the Fo raised during a 90 min period, then decreased to 85%. Fm and Fv decreased, also. The Fv/Fm and Y(II) diminished, while the non-regulated energy dissipation increased. The decrease of F0, Fm and Fv/Fm yield and that of the Y(II) certified the photoinhibition effect of 2100 μmol.m-2.s-1 light intensity on the activities carried out by the photosystems antenna. When an 800 μmol.m-2.s-1 light intensity was used the recovery of the photosynthetic activity was faster compared with other high-light intensities treatments. Keywords: chlorophyll fluorescence, maximal fluorescence Fm, minimal fluorescence F0, maximal PS II quantum yield (Fv/Fm), effective PS II quantum yield (YII), quantum yield of non-regulated energy dissipation (YNO), recovery, photoinhibition, coefficient of photochemical quenching (qP, qL).
 
         
     
         
         
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