Acetate in mixotrophic growth medium affects photosystem II in Chlamydomonas reinhardtii and protects against photoinhibition

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• 作者：Thomas Roach ; Arezki Sedoud ; Anja Krieger-Liszkay
• 关键词：Chl ; chlorophyll ; DCBQ ; 2 ; 6-dichloro-1 ; 4-benzoquinone ; DCMU ; 3-(3 ; 4-dichlorophenyl)-1 ; 1-dimethylurea ; Em ; midpoint redox potential ; Fm ; maximum chlorophyll fluorescence signal ; Fv ; variable chlorophyll fluorescence signal ; HSM ; high salt medium ; LHC ; ligh
• 刊名：Biochimica et Biophysica Acta (BBA)/Bioenergetics
• 出版年：2013
• 出版时间：October, 2013
• 年：2013
• 卷：1827
• 期：10
• 页码：1183-1190
• 全文大小：2337 K

文摘

Chlamydomonas reinhardtii is a photoautotrophic green alga, which can be grown mixotrophically in acetate-supplemented media (Tris-acetate-phosphate). We show that acetate has a direct effect on photosystem II (PSII). As a consequence, Tris-acetate-phosphate-grown mixotrophic C. reinhardtii cultures are less susceptible to photoinhibition than photoautotrophic cultures when subjected to high light. Spin-trapping electron paramagnetic resonance spectroscopy showed that thylakoids from mixotrophic C. reinhardtii produced less ¹O₂ than those from photoautotrophic cultures. The same was observed in vivo by measuring DanePy oxalate fluorescence quenching. Photoinhibition can be induced by the production of ¹O₂ originating from charge recombination events in photosystem II, which are governed by the midpoint potentials (E_m) of the quinone electron acceptors. Thermoluminescence indicated that the E_m of the primary quinone acceptor (Q_A/Q_A^?) of mixotrophic cells was stabilised while the E_m of the secondary quinone acceptor (Q_B/Q_B^?) was destabilised, therefore favouring direct non-radiative charge recombination events that do not lead to ¹O₂ production. Acetate treatment of photosystem II-enriched membrane fragments from spinach led to the same thermoluminescence shifts as observed in C. reinhardtii, showing that acetate exhibits a direct effect on photosystem II independent from the metabolic state of a cell. A change in the environment of the non-heme iron of acetate-treated photosystem II particles was detected by low temperature electron paramagnetic resonance spectroscopy. We hypothesise that acetate replaces the bicarbonate associated to the non-heme iron and changes the environment of Q_A and Q_B affecting photosystem II charge recombination events and photoinhibition.