ChloroSpec: A new in vivo chlorophyll fluorescence spectrometer for simultaneous wavelength- and time-resolved detection.

Chlorophyll fluorescence is a ubiquitous tool in basic and applied plant science research. Various standard commercial instruments are available for characterization of photosynthetic material like leaves or microalgae, most of which integrate the overall fluorescence signals above a certain cut-off wavelength. However, wavelength-resolved (fluorescence signals appearing at different wavelengths having different time dependent decay) signals contain vast information required to decompose complex signals and processes into their underlying components that can untangle the photo-physiological process of photosynthesis.

The role of the pigment-protein complex LHCBM1 in nonphotochemical quenching in Chlamydomonas reinhardtii.

Nonphotochemical quenching (NPQ) is the process that protects photosynthetic organisms from photodamage by dissipating the energy absorbed in excess as heat. In the model green alga Chlamydomonas reinhardtii, NPQ is abolished in the knock-out mutants of the pigment-protein complexes LHCSR3 and LHCBM1. However, while LHCSR3 is a pH sensor and switches to a quenched conformation at low pH, the role of LHCBM1 in NPQ has not been elucidated yet.

Drought affects both photosystems in Arabidopsis thaliana.

Drought is a major abiotic stress that impairs plant growth and development. Despite this, a comprehensive understanding of drought effects on the photosynthetic apparatus is lacking. In this work, we studied the consequences of 14-d drought treatment on Arabidopsis thaliana.

Weak acids produced during anaerobic respiration suppress both photosynthesis and aerobic respiration.

While photosynthesis transforms sunlight energy into sugar, aerobic and anaerobic respiration (fermentation) catabolizes sugars to fuel cellular activities. These processes take place within one cell across several compartments, however it remains largely unexplored how they interact with one another. Here we report that the weak acids produced during fermentation down-regulate both photosynthesis and aerobic respiration.

Photosynthetic Light Harvesting and Thylakoid Organization in a CRISPR/Cas9 Arabidopsis Thaliana LHCB1 Knockout Mutant.

Light absorbed by chlorophylls of Photosystems II and I drives oxygenic photosynthesis. Light-harvesting complexes increase the absorption cross-section of these photosystems. Furthermore, these complexes play a central role in photoprotection by dissipating the excess of absorbed light energy in an inducible and regulated fashion.

Molecular origins of induction and loss of photoinhibition-related energy dissipation q.

Photosynthesis fuels life on Earth using sunlight as energy source. However, light has a simultaneous detrimental effect on the enzyme triggering photosynthesis and producing oxygen, photosystem II (PSII). Photoinhibition, the light-dependent decrease of PSII activity, results in a major limitation to aquatic and land photosynthesis and occurs upon all environmental stress conditions.

Long-term adaptation of Arabidopsis thaliana to far-red light.

Vascular plants use carotenoids and chlorophylls a and b to harvest solar energy in the visible region (400-700 nm), but they make little use of the far-red (FR) light. Instead, some cyanobacteria have developed the ability to use FR light by redesigning their photosynthetic apparatus and synthesizing red-shifted chlorophylls. Implementing this strategy in plants is considered promising to increase crop yield.

PSI of the Colonial Alga Has an Unusually Large Antenna Size.

PSI is an essential component of the photosynthetic apparatus of oxygenic photosynthesis. While most of its subunits are conserved, recent data have shown that the arrangement of the light-harvesting complexes I (LHCIs) differs substantially in different organisms. Here we studied the PSI-LHCI supercomplex of a colonial green alga with potential for lipid and sugar production, using functional analysis and single-particle electron microscopy of the isolated PSI-LHCI supercomplexes complemented by time-resolved fluorescence spectroscopy in vivo.

Photosynthesis without β-carotene.

Carotenoids are essential in oxygenic photosynthesis: they stabilize the pigment-protein complexes, are active in harvesting sunlight and in photoprotection. In plants, they are present as carotenes and their oxygenated derivatives, xanthophylls. While mutant plants lacking xanthophylls are capable of photoautotrophic growth, no plants without carotenes in their photosystems have been reported so far, which has led to the common opinion that carotenes are essential for photosynthesis.

Disentangling the sites of non-photochemical quenching in vascular plants.

In nature, plants experience large fluctuations in light intensity and they need to balance the absorption and utilization of this energy appropriately. Non-photochemical quenching (NPQ) is a rapidly switchable mechanism that protects plants from photodamage caused by high light exposure by dissipating the excess absorbed energy as heat. It is triggered by the pH gradient across the thylakoid membrane and requires the protein PsbS and the xanthophyll zeaxanthin.

Exhibits De Facto Constitutive NPQ Capacity in Physiologically Relevant Conditions.

The photosynthetic apparatus must be able to withstand light conditions that exceed its capacity for carbon fixation. Photosynthetic organisms developed nonphotochemical quenching (NPQ), a process that dissipates excess absorbed light energy as heat and limits the production of reactive oxygen species and cellular damage. In the green alga , the LHCSR pigment-binding proteins are essential for NPQ.

pH dependence, kinetics and light-harvesting regulation of nonphotochemical quenching in .

Sunlight drives photosynthesis but can also cause photodamage. To protect themselves, photosynthetic organisms dissipate the excess absorbed energy as heat, in a process known as nonphotochemical quenching (NPQ). In green algae, diatoms, and mosses, NPQ depends on the light-harvesting complex stress-related (LHCSR) proteins.

The mechanism of cyclic electron flow.

Apart from the canonical light-driven linear electron flow (LEF) from water to CO, numerous regulatory and alternative electron transfer pathways exist in chloroplasts. One of them is the cyclic electron flow around Photosystem I (CEF), contributing to photoprotection of both Photosystem I and II (PSI, PSII) and supplying extra ATP to fix atmospheric carbon. Nonetheless, CEF remains an enigma in the field of functional photosynthesis as we lack understanding of its pathway.

Maximal cyclic electron flow rate is independent of PGRL1 in Chlamydomonas.

Cyclic electron flow (CEF) is defined as a return of the reductants from the acceptor side of Photosystem I (PSI) to the pool of its donors via the cytochrome bf. It is described to be complementary to the linear electron flow and essential for photosynthesis. However, despite many efforts aimed to characterize CEF, its pathway and its regulation modes remain equivocal, and its physiological significance is still not clear.

Lineage tracing of Notch1-expressing cells in intestinal tumours reveals a distinct population of cancer stem cells.

Colon tumours are hierarchically organized and contain multipotent self-renewing cells, called Cancer Stem Cells (CSCs). We have previously shown that the Notch1 receptor is expressed in Intestinal Stem Cells (ISCs); given the critical role played by Notch signalling in promoting intestinal tumourigenesis, we explored Notch1 expression in tumours. Combining lineage tracing in two tumour models with transcriptomic analyses, we found that Notch1+ tumour cells are undifferentiated, proliferative and capable of indefinite self-renewal and of generating a heterogeneous clonal progeny.

Chlororespiration Controls Growth Under Intermittent Light.

Whereas photosynthetic function under steady-state light conditions has been well characterized, little is known about its changes that occur in response to light fluctuations. Chlororespiration, a simplified respiratory chain, is widespread across all photosynthetic lineages, but its role remains elusive. Here, we show that chlororespiration plays a crucial role in intermittent-light conditions in the green alga Chlororespiration, which is localized in thylakoid membranes together with the photosynthetic electron transfer chain, involves plastoquinone reduction and plastoquinol oxidation by a Plastid Terminal Oxidase (PTOX).

State transitions redistribute rather than dissipate energy between the two photosystems in Chlamydomonas.

Photosynthesis converts sunlight into biologically useful compounds, thus fuelling practically the entire biosphere. This process involves two photosystems acting in series powered by light harvesting complexes (LHCs) that dramatically increase the energy flux to the reaction centres. These complexes are the main targets of the regulatory processes that allow photosynthetic organisms to thrive across a broad range of light intensities.

The plastid terminal oxidase: its elusive function points to multiple contributions to plastid physiology.

Plastids have retained from their cyanobacterial ancestor a fragment of the respiratory electron chain comprising an NADPH dehydrogenase and a diiron oxidase, which sustain the so-called chlororespiration pathway. Despite its very low turnover rates compared with photosynthetic electron flow, knocking out the plastid terminal oxidase (PTOX) in plants or microalgae leads to severe phenotypes that encompass developmental and growth defects together with increased photosensitivity. On the basis of a phylogenetic and structural analysis of the enzyme, we discuss its physiological contribution to chloroplast metabolism, with an emphasis on its critical function in setting the redox poise of the chloroplast stroma in darkness.

Transient states in electrical circuits with a nanowire.

We have observed conductance quantization of macroscopic metallic contacts in a circuit with a mechanical relay and LC circuit. The investigation has been performed outdoors at room temperature, and it was focused on measuring the conductance between two vibrating metal wires. Transient states of the current in a circuit are also described in the paper, this description includes a contact with quantized conductance.