PARENT SESSION
Posters P3C C3 and Rubisco. Abstracts (617-630)

Photosynthetic electron transport properties of the rbcL deletion mutant of tobacco. Yagut Allahverdiyeva^*,1, Imre Vass², Pirkko Mäenpää¹, Eva-Mari Aro¹, ¹ Department of Biology, Plant Physiology and Molecular Biology, University of Turku, Turku, Finland² Plant Biology Institute, H-6701, Szeged, Hungary

ABSTRACT- We have studied a tobacco rbcL deletion mutant, which lacks the large subunit of Rubisco, the key enzyme of photosynthetic carbon assimilation. Mutant was grown photoheterotrophically in the presence of sucrose and was sensitive to light. Detailed studies of electron transport properties of the thylakoid membrane, performed by flash induced fluorescence relaxation and thermoluminescence measurements, revealed that deletion of rbcL clearly affects the acceptor side of the PSII complex. The fast and the middle phases of flash-induced fluorescence relaxation in the absence of DCMU were significantly slowed down in the mutant, which indicates a modification in the QA to QB electron transfer and the PQ pool. Importantly, the thermoluminescence B band, which originates from S2QB- charge recombination, was shifted to lower temperature in the mutant as compared to WT, which is in good agreement with the effect of rbcL deletion mutation on the QB site. On the other hand, the thermoluminescence Q band, originating from S2QA- recombination, was not affected by mutation, indicating that the donor side function of the PSII complex was not impaired. This was in accordance with the kinetics of the flash induced fluorescence relaxation in the rbcL deletion thylakoids in the presence of DCMU. 77K fluorescence emission spectra revealed a band at 680 nm and a blue shift at 730 nm in the rbcL mutant thylakoids, implying a presence of free LHC complexes.The maximum level of photooxidisible P700 in rbcL mutant thylakoids, measured by excitation of the samples with saturating single turnover flash, was lower than in WT samples. This result is in accordance with the fluorescence measurements of PSII electron transport activities confirms an increased ratio of PSII to PSI in rbcL mutant thylakoids. Observed modifications of the thylakoid protein complexes in the rbcL mutant are probably a result of chronic photoinhibition.

KEY WORDS: Photosystem II, Rubisco, Photosystem I, Photoinhibition