As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

BIOPHYSICAL BASIS O F FLUORESCENCE EMISSION FROM CHLOROPLASTS . . . . .. . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . 314 Fluorescence as a Reaction Competing in the Deactivation of Excited Chlorophyll . . . . . . . . . . ... . . .. . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Lifetimes of Fluorescence . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . 317 Origin of Fluorescence Emission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 1 Fluorescence of PS 11 and PS I at Ambient and Low Temperatures . . . . . . . . . . . . . . . . . . . 323 FLUORESCENCE INDUCTION AND PS II HETEROGENEITy 325 Fluorescence Transient from Fo to FM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 The FI Level and Inactive PS11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... .... . .. . . . .. . . . . . . . . . 326 Fluorescence Induction in High Ught .. . . . . . . . . 327 Rise in the Presence of DCMU and a/{3 Heterogeneity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327 FLUORESCENCE QUENCHING 329 Resolution of Quenching Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . ........ . .. . . . . . . . . . . . . . . 330 Mechanism of Energy·Dependent Quenching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 1 Quenching Related t o State Transition . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . .. . ......... . . .. .. . . . . . . . 334 Photoinhibitory Quenching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334 Further Quenching Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 Physiological Aspects of Quenching . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 338 CONCLUSIONS AND PERSPECTiVES 341

Chlorophyll Fluorescence and Photosynthesis: The Basics

An overview of the self-organizing map algorithm, on which the papers in this issue are based, is presented in this article.

The Self-Organizing Map

PHOTO PROTECTION 604 Prevention oj Excessive Light Absorption... 604 Removal of Excess Excitation Energy Directly within the Light-Capturing System ......... ...... . . ..... ..... . .... . ..... ...... .... . .. . .. . . ..... . . . ... ... . 604 Removal oj Active Oxygen Formed in the Photochemical Apparatus ........ . . .. . . . . . . 605 INACTIV A TIONiTURNOVER OF PS II 606 THE XANTHOPHYLL CYCLE AND THERMAL ENERGY DISSIPATION: A PHOTOPROTECTIVE RESPONSE 608 Characteristics oj the Xanthophyll Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 608 Association Among the De-epoxidized State oj the Xanthophyll Cycle, Thermal Energy Dissipation. and Photoprotection .. .. . . . .. . . ...... .. .. ... ... 609 Operation of the Xanthophyll Cycle in the Field . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . .... . . . .. . . . . 611 CONCLUSIONS 618

Photoprotection and Other Responses of Plants to High Light Stress

Photoinhibition of photosystem II : inactivation, protein damage and turnover

subcellular levels. ChlF is now measurable from remote sensing platforms. This provides a new optical means to track photosynthesis and gross primary productivity of terrestrial ecosystems. Importantly, the spatiotemporal and methodological context of the new applications is dramatically different compared with most of the available ChlF literature, which raises a number of important considerations. Although we have a good mechanistic understanding of the processes that control the ChlF signal over the short term, the seasonal link between ChlF and photosynthesis remains obscure. Additionally, while the current understanding of in vivo ChlF is based on pulse amplitude-modulated (PAM) measurements, remote sensing applications are based on the measurement of the passive solar-induced chlorophyll fluorescence (SIF), which entails important differences and new challenges that remain to be solved. In this review we introduce and revisit the physical, physiological, and methodological factors that control the leaf-level ChlF signal in the context of the new remote sensing applications. Specifically, we present the basis of photosynthetic acclimation and its optical signals, we introduce the physical and physiological basis of ChlF from the molecular to the leaf level and beyond, and we introduce and compare PAM and SIF methodology. Finally, we evaluate and identify the challenges that still remain to be answered in order to consolidate our mechanistic understanding of the remotely sensed SIF signal.

/pdf/linking-chlorophyll-a-fluorescence-to-photosynthesis-for-1ouimcww8h.pdf

Linking chlorophyll a fluorescence to photosynthesis for remote sensing applications: mechanisms and challenges

Pumpkin leaves grown under high light (500-700 micromol of photons m-2.s-1) were illuminated under photon flux densities ranging from 6.5 to 1500 micromol.m-2.s-1 in the presence of lincomycin, an inhibitor of chloroplast protein synthesis. The illumination at all light intensities caused photoinhibition, measured as a decrease in the ratio of variable to maximum fluorescence. Loss of photosystem II (PSII) electron transfer activity correlated with the decrease in the fluorescence ratio. The rate constant of photoinhibition, determined from first-order fits, was directly proportional to photon flux density at all light intensities studied. The fluorescence ratio did not decrease if the leaves were illuminated in low light in the absence of lincomycin or incubated in darkness in the presence of lincomycin. The constancy of the quantum yield of photoinhibition under different photon flux densities strongly suggests that photoinhibition in vivo occurs by one dominant mechanism under all light intensities. This mechanism probably is not the acceptor side mechanism characterized in the anaerobic case in vitro. Furthermore, there was an excellent correlation between the loss of PSII activity and the loss of the D1 protein from thylakoid membranes under low light. At low light, photoinhibition occurs so slowly that inactive PSII centers with the D1 protein waiting to be degraded do not accumulate. The kinetic agreement between D1 protein degradation and the inactivation of PSII indicates that the turnover of the D1 protein depends on photoinhibition under both low and high light.

https://www.pnas.org/content/pnas/93/5/2213.full.pdf

The rate constant of photoinhibition, measured in lincomycin-treated leaves, is directly proportional to light intensity.

Photoinhibition of Photosystem II (PSII) is the light-induced loss of PSII electron-transfer activity. Although photoinhibition has been studied for a long time, there is no consensus about its mechanism. On one hand, production of singlet oxygen ((1)O(2)) by PSII has promoted models in which this reactive oxygen species (ROS) is considered to act as the agent of photoinhibitory damage. These chemistry-based models have often not taken into account the photophysical features of photoinhibition-like light response and action spectrum. On the other hand, models that reproduce these basic photophysical features of the reaction have not considered the importance of data about ROS. In this chapter, it is shown that the evidence behind the chemistry-based models and the photophysically oriented models can be brought together to build a mechanism that confirms with all types of experimental data. A working hypothesis is proposed, starting with inhibition of the manganese complex by light. Inability of the manganese complex to reduce the primary donor promotes recombination between the oxidized primary donor and Q(A), the first stable quinone acceptor of PSII. (1)O(2) production due to this recombination may inhibit protein synthesis or spread the photoinhibitory damage to another PSII center. The production of (1)O(2) is transient because loss of activity of the oxygen-evolving complex induces an increase in the redox potential of Q(A), which lowers (1)O(2) production.

Photoinhibition of Photosystem II

Evidence for the role of the oxygen-evolving manganese complex in photoinhibition of Photosystem II.

Photoinhibition of photosystem II was studied in vivo with bean (Phaseolus vulgaris) plants grown in the presence of 03 (control), 4, or 15 μm Cu2+ Although photoinhibition, measured in the presence of lincomycin to block concurrent recovery, is faster in leaves of Cu2+-treated plants than in control leaves, thylakoids isolated from Cu-treated plants did not show high sensitivity to photoinhibition Direct effects of excess Cu2+ on chloroplast metabolism are actually unlikely, because the Cu concentration of chloroplasts of Cu-treated plants was lower than that of their leaves Excess Cu in the growth medium did not cause severe oxidative stress, collapse of antioxidative defenses, or loss of photoprotection Thus, these hypothetical effects can be eliminated as causes for Cu-enhanced photoinhibition in intact leaves However, Cu treatment lowered the leaf chlorophyll (Chl) concentration and reduced the thylakoid membrane network The loss of Chl and sensitivity to photoinhibition could be overcome by adding excess Fe together with excess Cu to the growth medium The addition of Fe lowered the Cu2+ concentration of the leaves, suggesting that Cu outcompetes Fe in Fe uptake We suggest that the reduction of leaf Chl concentration, caused by the Cu-induced iron deficiency, causes the high photosensitivity of photosystem II in Cu2+-treated plants A causal relationship between the susceptibility to photoinhibition and the leaf optical density was established in several plant species Plant species adapted to high-light habitats apparently benefit from thick leaves because the rate of photoinhibition is directly proportional to light intensity, but photosynthesis becomes saturated by moderate light

/pdf/excess-copper-predisposes-photosystem-ii-to-photoinhibition-4pk5f3tr1q.pdf

Esa Tyystjärvi

Papers

Linking chlorophyll a fluorescence to photosynthesis for remote sensing applications: mechanisms and challenges

The rate constant of photoinhibition, measured in lincomycin-treated leaves, is directly proportional to light intensity.

Photoinhibition of Photosystem II

Evidence for the role of the oxygen-evolving manganese complex in photoinhibition of Photosystem II.

Excess Copper Predisposes Photosystem II to Photoinhibition in Vivo by Outcompeting Iron and Causing Decrease in Leaf Chlorophyll