强闪光抑制棉花叶片光系统Ⅱ活性和热耗散

Repetitive intense flashes inhibit photosystem Ⅱ activity and thermal dissipation in cotton leaves

除持续强光导致光合作用效率降低外,强闪光也能够影响光合功能,但规律和机制尚不清楚。为研究强闪光对喜光植物棉花叶片光合功能的影响,选用陆地棉(Gossypium hirsutum L.)品种新陆早45号为材料,于强闪光处理(20,000μmol m–2 s–1, 300 ms,间隔10 s,处理时间持续30 min)前后分别测定叶绿素荧光、P700和气体交换。结果表明,强闪光处理后不仅有活性的PSI (光系统I)反应中心含量下降,同时PSⅡ (光系统Ⅱ)电子传递活性也受到限制。与对照相比,强闪光处理后PSI的ΦND (PSI供体侧限制引起的非光化学量子产量)下降,ΦNA (PSI受体侧限制引起的非光化学量子产量)增加,暗示强闪光能够抑制PSI受体侧电子传递活性。强闪光处理不仅使PSⅡ的实际量子产量明显下降,而且非光化学猝灭和ΦNPQ (PSⅡ调节性能量耗散的量子产量)也降低;但是,ΦNO (PSⅡ非调节性能量耗散的量子产量)明显增加,表明强闪光导致热耗散降低和PSⅡ失活。此外,强闪光处理后光合速率和气孔导度均降低,但细胞间隙CO2浓度增加,证明强闪光处理后同化能力的降低不是气孔限制导致的。因此,本研究认为强闪光处理不仅抑制PSI活性,而且导致PSⅡ失活和可调节性热耗散下降;光合电子传递活性的下降可能是强闪光下光合速率降低的重要原因。

Not only continuous high light results in the decrease of photosynthetic efficiency,but also intense flashes may affect the photosynthetic function.In this study,cotton(Gossypium hirsutum L.)cultivar Xinluzao 45 was used to investigate the effects of repetitive intense flash treatment(leaves exposed to 20,000μmol m^–2 s^–1 for 300 ms,with interval time of 10 s,and the whole treatment duration was 30 min)on two photosystems and photosynthetic function of cotton leaves.Chlorophyll fluorescence,P700 and gas exchange were measured before and after repetitive intense flash treatment,respectively.The content of active PSI(photosystem I)reaction center and the electron transfer activity of PSⅡ(photosystemⅡ)all decreased after repetitive intense flash treatment which reflected by the significant increase in J and K phases of the fluorescence induction kinetics curves after repetitive intense flash treatment.ΦND(the quantum yield of non-photochemical energy dissipation due to donor side limitation)of PSI decreased whileΦNA(the quantum yield of non-photochemical energy dissipation due to acceptor side limitation)increased,indicating that acceptor side of PSI was primarily inhibited by repetitive intense flashes.Repetitive intense flash treatment induced a distinct decrease in the quantum yield of PSⅡin cotton leaves under actinic light.Moreover,ΦNPQ(the quantum yield of regulated energy dissipation)of PSⅡdecreased significantly after repetitive intense flash treatment.However,ΦNO(the quantum yield of non-regulated energy dissipation)increased considerably,demonstrating that the repetitive intense flashes caused PSⅡphotoinhibition.The photosynthetic rate and the stomatal conductance decreased while the intercellular CO2 concentration increased after repetitive intense flash treatment,indicating that the reduction of carbon assimilation induced by repetitive intense flash treatment is not limited by stomata.Therefore,we believe that the repetitive intense flash treatment not only induces inactivation of PSI,but also leads to PSⅡphotoinhibition and the decrease of thermal dissipation.The suppression of photosynthetic electron transport activity may play important role in the decrease of photosynthetic rate after repetitive intense flash treatment.