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    STUDIA BIOLOGIA - Ediţia nr.1 din 2006  
         
  Articol:   EXCITATION PRESSURE AND ENERGY NONPHOTOCHEMICAL DISSIPATION UNDER EXCESS LIGHT IN Mugeotia sp., GREEN ALGA STRAIN AICB 560.

Autori:  VICTOR BERCEA, BOGDAN DRUGĂ, CĂTĂLINA VASILESCU, NICOLAE DRAGOŞ. 		 
       
         
  Rezumat:  Excitation pressure effects on PS II under light excess and nonphotochemical dissipation of excitation energy (qN) concomitantly with violaxanthin de-epoxidation in green alga Mugeotia sp. are presented. Light intensities of 1500, 3000 and 4500 µmol.m-2.s-1 were applied for 120 minutes in the alga exponential growth phase. The excitation pressure on PS II reaction centers enhanced under 1500 µmol.m-2.s-1, increasing the number of closed (reduced) Q-A while the photochemical reactions decreased and qN. At high light, the excitation pressure decreased, being correlated to qp increment, which denotes a Q-A reoxidation, possible due to stromatic reactants that operate on plastoquinone pool through the chlororespiration. The qN enhanced meaning that the reaction centers were gradually closed with the exposure period. Violaxantin de-epoxidation that was observed by absorption changes at 505 nm enhanced with the exposure period leading to zeaxanthin enhancement, being correlated with qN. De-epoxidation was correlated with the tylacoidal membrane conformational changes displayed by the absorption changes at 535 nm and 700 nm. During the post-illumination period, qp has decreased with the reduction of the qN in the absence of light. KEYWORDS: chlorophyll fluorescence; PS II and PS I reaction centers; primary acceptor; redox state; violaxanthin de-epoxidation.  
         
     
         
         
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