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Ascorbic Acid
Published in Ruth G. Alscher, John L. Hess, Antioxidants in Higher Plants, 2017
Oxygen competes with NADP for reducing equivalents (Figure 7). Electron flow to oxygen has always been considered to be rather low under steady-state conditions, accounting for less than 20% of the net steady-state rate of oxygen evolution during CO2 assimilation at high irradiances.87,88 However, when CO2 assimilation is restricted and the NADP pool becomes relatively reduced, electron flow to O2 is favored. Such a situation arises during the induction phase of photosynthesis that follows a transition from darkness to light or a transition from low irradiance to high irradiance.89-92 In this situation, over-reduction is necessary to force the thiol-dependent activation of the light-modulated enzymes of the Benson-Calvin cycle.90 During the induction phase, the processes of psudocyclic and cyclic electron flow serve to generate ATP because noncyclic electron flow is limited by the availability of NADP.90 Once the thiol-modulated enzymes of the Benson-Calvin cycle are activated, the turnover of this cycle increases the demand for NADPH, and ATP also increases such that the NADPH to NADP ratio falls to a level very close to the dark value, and noncyclic electron flow is predominant.90
Crystallizing Membrane Proteins: Experiments on Different Systems
Published in Hartmut Michel, Crystallization of Membrane Proteins, 1991
As in plants, cyanobacteria have two photosystems in their photosynthetic apparatus: photosystem II which is involved in oxygen evolution and H+ pumping and photosystem I which provides reducing equivalents for the production of NADPH.42 Intact and active photosystem I reaction center (PS1-rc) complexes can be easily isolated from a number of cyanobacteria. From the thermophilic cyanobacterium Phormidium laminosum, we have isolated a 450 kDa complex which is stable in a number of detergents including SDS10. The PS1-rc is an extremely heterogeneous complex consisting of at least four distinct polypeptides, iron-suffer centers, and about 60 light-harvesting pigment molecules. The proper choice of detergent is very important here as we wish to keep this complex intact. Some small detergent like β-OG are inadequate for this task and result in pigment loss. Instead, the PS1-rc complex was generally handled in Triton X-100 or dodecyl maltoside (C12-M).
Carbon Dioxide Sequestration by Microalgae
Published in Gokare A. Ravishankar, Ranga Rao Ambati, Handbook of Algal Technologies and Phytochemicals, 2019
G.V. Swarnalatha, Ajam Shekh, P.V. Sijil, C.K. Madhubalaji, Vikas Singh Chauhan, Ravi Sarada
The photosynthetic growth of the microalgae and their CO2 fixation ability is influenced by the light intensity. Light intensity is a limiting factor which influences photosynthesis process, CO2 fixation, biomass production, and overall metabolic activity and growth of microalgae. High light intensities also cause photo inhibition for surface layer of algae. The daily growth rate of microalgae with respect to biomass is increased by avoiding photo inhibition (Chisti 2007). Increased removal of CO2 by C. vulgaris and D. tertiolecta was noted with increase in light intensity (10, 20, and 50 Wm−3 under 4% CO2 supplementation (Hulatt and Thomas 2011)). Also, 4.2-fold increased biomass production was noted for cyanobacterium Synechococcus sp. with increasing light intensity from 156 to 1250 lx (2.5–20 µE m−2 s−1). In general, increasing light intensity generally increases microalgal CO2 fixation rates. Oxygen evolution and CO2 capture will have a positive correlation with increasing light intensity till reaching the light saturation point (Fan et al. 2007). Chlorella sp. was investigated with sunlight, xenon lamps, and fluorescent lamps, and it has variable effects on CO2 fixation rates. Researchers concluded that the highest CO2 fixation rate (0.865 g L−1 d−1), biomass productivity (0.437 g L−1 d−1), and biomass concentration (0.842 g L−1) were achieved with white fluorescent lamps (Hirata et al. 1996). The self-shading effect of microalgal cells also affects the light distribution in the culture. Self-shading, therefore, leads to decreased productivities. However, in the case of airlift photobioreactor systems, this limitation can be overcome by sparging air from the bottom which increases the light delivery to the cells due to Brownian motion.
Mechanism of long-term toxicity of CuO NPs to microalgae
Published in Nanotoxicology, 2018
Xingkai Che, Ruirui Ding, Yuting Li, Zishan Zhang, Huiyuan Gao, Wei Wang
The net photosynthetic O2 evolution activities and the respiratory O2 uptake activities were measured at 25 °C with an Oxytherm O2 electrode (Hansatech, UK) according to Zhang et al. (Zhang et al. 2011; Zhang, He, and Liu 2014). About 1.9mL algae medium was placed into electrode chamber to which 0.1mL saturated KHCO3 were added to generate sufficient CO2 for the photosynthetic reaction. Subsequently, electrode chamber was sealed by electrode lib and then O2 evolution was measured under actinic light intensities (800mmol/m2/s). Dark respiration was estimated from O2 uptake by cells incubated in the dark. The rate of true photosynthesis is equal to the sum of oxygen evolution and dark respiration.