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Plastids - Plant Cell Biology For Masters- by G. R. Kantharaj

Photosynthesis - Wikipedia

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MIRON Violett Glas | Biophotonics | Biophotonic

Submergence is a common type of environmental stress for plants. It hampers survival and decreases crop yield, mainly by inhibiting plant photosynthesis. The inhibition of photosynthesis and photochemical efficiency by submergence is primarily due to leaf senescence and excess excitation energy, caused by signals from hypoxic roots and inhibition of gas exchange, respectively. However, the influence of mere leaf-submergence on the photosynthetic apparatus is currently unknown. Therefore, we studied the photosynthetic apparatus in detached leaves from four plant species under dark-submergence treatment (DST), without influence from roots and light. Results showed that the donor and acceptor sides, the reaction center of photosystem II (PSII) and photosystem I (PSI) in leaves were significantly damaged after 36 h of DST. This is a photoinhibition-like phenomenon similar to the photoinhibition induced by high light, as further indicated by the degradation of PsaA and D1, the core proteins of PSI and PSII. In contrast to previous research, the chlorophyll content remained unchanged and the H2O2 concentration did not increase in the leaves, implying that the damage to the photosynthetic apparatus was not caused by senescence or over-accumulation of reactive oxygen species (ROS). DST-induced damage to the photosynthetic apparatus was aggravated by increasing treatment temperature. This type of damage also occurred in the anaerobic environment (N2) without water, and could be eliminated or restored by supplying air to the water during or after DST. Our results demonstrate that DST-induced damage was caused by the hypoxic environment. The mechanism by which DST induces the photoinhibition-like damage is discussed below.

Plastid is another important energy transducing cell organelle found only in plants

To further investigate the effect of O2 on the photosynthetic apparatus after 36 h of DST, air or N2 were pumped into the water, and the photochemical activity of leaves was analyzed after 36 h of DST. Results showed that both the Ψo and Fv/Fm recovered to 93.2%~100% of the control after pumping air into the water after 36 h of DST (). However, both Ψo and Fv/Fm continuously declined after N2 was pumped into the water (), which indicates that the damage to the photosynthetic apparatus was effectively recovered by supplying O2 after DST. This result further demonstrates that the damage of the photosynthetic apparatus caused by DST is caused by the hypoxic condition of the water.

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Signals from hypoxic roots and light-induced excess excitation energy are harmful to the photosynthetic apparatus. However, it is unclear whether mere leaf submergence affects photosynthetic activity without the influence of the factors mentioned above.

Most previous studies show that the photosynthesis rate and photochemical efficiency decrease in the leaves of submerged plants , , . The decline in activity of the photosynthetic apparatus is induced, firstly, by the inhibition of root respiration by low O2 levels in submerged soil, which decreases the absorptive capacity for water and nutrients , , . Secondly, signals such as abscisic acid (ABA) and ethylene from the hypoxic roots lead to stomatal closure and leaf senescence, thereby inhibiting photosynthesis and causing photoinhibition , , . Thirdly, the low CO2 concentration in water inhibits photosynthetic carbon assimilation, triggering excess excitation energy –.

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Max Bracher All living organisms consist of cells, whether bacterium, plant, animal or human

Decarbonization of the transport system and a transition to a new diversified energy system that is scalable and sustainable, requires a widespread implementation of carbon-neutral fuels. In biomimetic supramolecular nanoreactors for solar-to-fuel conversion, water-splitting catalysts can be coupled to photochemical units to form complex electrochemical nanostructures, based on a systems integration approach and guided by magnetic resonance knowledge of the operating principles of biological photosynthesis, to bridge between long-distance energy transfer on the short time scale of fluorescence, ~10−9 s, and short-distance proton-coupled electron transfer and storage on the much longer time scale of catalysis, ~10−3 s. A modular approach allows for the design of nanostructured optimized topologies with a tunneling bridge for the integration of storage with catalysis and optimization of proton chemical potentials, to mimic proton-coupled electron transfer processes in photosystem II and hydrogenase.

Xanthophylls (oxygenated carotenoids) are also found in zooxanthellae. Two xanthophylls (diadinoxanthin and diatoxanthin) play an important role in protecting symbiotic algae and coral hosts from excessive light energy. When light energy is sufficient enough to effect pH changes within the photosynthetic apparatus of zooxanthellae, diadinoxanthin is converted to diatoxanthin. This conversion shunts light energy away from photosynthesis. In darkness, the process reverses, and diatoxanthin becomes diadinoxanthin. Note that these xanthophylls both absorb some violet but most strongly blue wavelengths at ~450 - 490nm. See Figure 28.

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Photosynthetic response of Populus euphratica to salt ..

In nature, the photosynthetic apparatus is connected to a steady-state network of catalytic conversion reactions in the organism that is continuously dissipating energy and generating entropy. From a biological perspective, photosynthesis is an expensive process in terms of resources required, and organisms generally produce only the photosynthetic capacity that they need to serve their requirements within the limits of the environmental and developmental constraints. At low light intensities, however, the productive storage of energy is an efficient chemical thermodynamics process, which is optimized against depletion by wasteful back reactions that feed into the decay of the absorber with rate g = 1/τ from the excited chlorophyll state into the ground state at the start of the conversion chain []. Natural photosynthesis requires coupling of primary conversion into biochemical networks and catalytic cycles that are subject to regulation for protection against excess light, leading to limited photosynthetic capacity. In contrast, for artificial photosynthesis it is necessary to consider the minimal design requirements for the most efficient solar-to-fuel conversion process, operating close to the theoretical limits on solar energy conversion.

View and Download Heinz Walz JUNIOR PAM operator's manual ..

To understand how thermodynamic constraints can guide the design of artificial systems for photochemical storage, it is best to start from minimal models that consider the thermodynamic constraints on the photovoltaic or photochemical solar energy conversion by exploring the analogy with efficient conversion in the solar or photovoltaic cell [–]. In productive photochemical conversion, the storage or downstream utilization is described as a single step conversion of solar energy into Gibbs free energy. Like the silicon solar cell, the photosynthetic solar cell is in its simplest form a molecular absorber that is excited and produces energy conversion by charge separation with rate I into an electron and hole in dynamic equilibrium with the absorber (Fig. ). The excitation of a molecular Chl absorber in exchange with the field of solar irradiation leads to a difference in chemical potential

idling state of photosynthesis at which PS ..

Although solar energy plays a major role in all scenarios for a secure, sustainable and efficient energy supply, direct solar-to-fuel conversion remains a distant goal due to major scientific and technological challenges. During his career, Lubitz et al. [] has been one of the pioneers in the scientific underpinning of the principles of photosynthetic energy conversion, with a particular focus on resolving molecular mechanisms of multi-electron catalysis in photosystem II and in hydrogenases. The recent scientific breakthroughs in basic research in photosynthesis have made it possible to learn from Nature how to construct artificial devices that can be put to use for harnessing solar energy for sustainable production of primary energy carriers, like hydrogen from water or carbon-based fuels from CO2. Building bio-inspired photoelectrochemical cells for fuel production from solar energy will require the development and systems design of integrated supramolecular modular systems that combine functionalities for light harvesting, charge separation, proton-coupled electron transfer and multi-electron catalysis (Fig. ). With a nanostructured device, it is possible to use the physical–chemical principles for efficient photochemical conversion and storage at early stages of natural photosynthesis as a blueprint for the construction of artificial systems that convert solar energy into fuel in a rational higher order supramolecular assembly design by systems integration. The crucial point that is brought forward in this contribution, is that a full merger between catalysis and storage will allow for optimal matching of time, length and energy scales for solar energy to fuel conversion [].

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