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Raymond A. Cloyd, Cindy L. Galle, Stephen R. Keith, and Kenneth E. Kemp

mitochondria electron transport inhibitors or METIs ( Ware and Whitacre, 2004 ; Yu, 2008 ). The mitochondrion (plural: mitochondria) is a membrane-bounded organelle that is associated with intracellular respiration. The mitochondrion is a major site of

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Shuang Han, Jiafu Jiang, Huiyun Li, Aiping Song, Sumei Chen, and Fadi Chen

., 2002 ), since this technique delivers information regarding the saturation characteristics of electron transport, as well as being able to quantify overall photosynthetic performance ( Ralph and Gademann, 2005 ). A clear effect of low light intensity

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Lailiang Cheng, Leslie H. Fuchigami, and Patrick J. Breen

Bench-grafted `Fuji' apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] trees on Malling 26 (M.26) rootstocks were fertigated for 6 weeks with N concentrations ranging from 0 to 20 mm. These treatments produced levels of leaf N ranging from 0.9 to 4.3 g·m-2. Over this range, leaf absorptance increased curvilinearly from 74.8% to 92.5%. The light saturation point for CO2 assimilation expressed on the basis of absorbed light increased linearly at first with increasing leaf N, then reached a plateau at a leaf N content of ≈3 g·m-2. Under high light conditions (photosynthetic photon flux of 1500 μmol·m-2·s-1), the amount of absorbed light in excess of that required to saturate CO2 assimilation decreased with increasing leaf N. Chlorophyll fluorescence measurements revealed that the maximum photosystem II (PSII) efficiency of dark-adapted leaves was relatively constant over the leaf N range, except for a slight decrease at the lower end. As leaf N increased, nonphotochemical quenching declined under high light, and there was an increase in the efficiency with which the absorbed photons were delivered to open PSII centers. The photochemical quenching coefficient remained high except for a decrease at the lower end of the leaf N range. Actual PSII efficiency increased curvilinearly with increasing leaf N, and was highly correlated with light-saturated CO2 assimilation. The fraction of absorbed light potentially going into singlet oxygen formation was estimated to be ≈10%, regardless of leaf N status. It was concluded that there was more excess absorbed light in low N leaves than in high N leaves under high light conditions. Nonphotochemical quenching was enhanced with decreasing leaf N to reduce both the PSII efficiency and the probability of damage from photooxidation by excess absorbed light.

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Shuyang Zhen and Marc W. van Iersel

dissipated as heat and a small fraction is re-emitted as chlorophyll fluorescence ( Maxwell and Johnson, 2000 ). The quantum yield of photosystem II, the efficiency with which photosystem II (PSII) uses absorbed photons for electron transport, or the moles of

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Geoffrey Weaver and Marc W. van Iersel

hydrogen (NADPH) via the electron transport chain, and a proton gradient across the thylakoid membrane drives adenosine triphosphate (ATP) synthase, regenerating ATP. These energy-rich molecules—NADPH and ATP—provide the reducing power and chemical energy

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Marc W. van Iersel, Geoffrey Weaver, Michael T. Martin, Rhuanito S. Ferrarezi, Erico Mattos, and Mark Haidekker

estimate electron transport rate through PSII ( Baker and Rosenqvist, 2004 ; Genty et al., 1989 ). Because chlorophyll fluorescence is relatively easy to measure and provides detailed physiological information, such measurements can be a valuable tool to

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Steven J. McArtney, John D. Obermiller, and Consuelo Arellano

electron transfer between the primary and secondary quinones of PSII (see Abbaspoor et al., 2006 , and references cited therein). Interruption of photosynthetic electron transport inhibits adenosine 5′-triphosphate production and carbon fixation. If this

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Meijun Zhang, Duanduan Zhao, Zengqiang Ma, Xuedong Li, and Yulan Xiao

were the same as the first experiment for the PM and PA treatments, respectively. The experiment was conducted once. Chlorophyll content, the ratio of variable to maximum chlorophyll fluorescence (F v /F m ), and electron transport rate (ETR) were not

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Yuting Meng, Boling Liu, Ping Zhang, Ping Cui, Yuguang Song, Nianwei Qiu, Guoliang Han, and Feng Zhou

the membranes directly and affect the electron transport of chloroplasts and mitochondria, leading to the electron leakage and the generation of ROS ( Begović et al., 2016 ; Pazin et al., 2015 ; Pereira et al., 2013 ; Qiu et al., 2018 ). The

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Zengqiang Ma, Shishang Li, Meijun Zhang, Shihao Jiang, and Yulan Xiao

) and calculated using the formula of Moran (1982) . The ratio of variable to maximum chlorophyll fluorescence (F v /F m ) and electron transport rate (ETR) were measured and calculated with a Maxi-Imaging-PAM chlorophyll fluorescence measuring system