Tailoring confocal microscopy for real-time analysis of photosynthesis at single-cell resolution

Photoautotrophs' environmental responses have been extensively studied at the organism and ecosystem level. However, less is known about their photosynthesis at the single-cell level. This information is needed to understand photosynthetic acclimation processes, as light changes as it penetrates cells, layers of cells, or organs. Furthermore, cells within the same tissue may behave differently, being at different developmental/physiological stages. Here, we describe an approach for single-cell and subcellular photophysiology based on the customization of confocal microscopy to assess chlorophyll fluorescence quenching by the saturation pulse method. We exploit this setup to (1) reassess the specialization of photosynthetic activities in developing tissues of non-vascular plants; (2) identify a specific subpopulation of phytoplankton cells in marine photosymbiosis, which consolidate energetic connections with their hosts; and (3) examine the link between light penetration and photoprotection responses inside the different tissues that constitute a plant leaf anatomy.

A metabolic, phylogenomic and environmental atlas of diatom plastid transporters from the model species Phaeodactylum

Diatoms are an important group of algae, contributing nearly 40% of total marine photosynthetic activity. However, the specific molecular agents and transporters underpinning the metabolic efficiency of the diatom plastid remain to be revealed. We performed in silico analyses of 70 predicted plastid transporters identified by genome-wide searches of Phaeodactylum tricornutum. We considered similarity with Arabidopsis thaliana plastid transporters, transcriptional co-regulation with genes encoding core plastid metabolic pathways and with genes encoded in the mitochondrial genomes, inferred evolutionary histories using single-gene phylogeny, and environmental expression trends using Tara Oceans meta-transcriptomics and meta-genomes data. Our data reveal diatoms conserve some of the ion, nucleotide and sugar plastid transporters associated with plants, such as non-specific triose phosphate transporters implicated in the transport of phosphorylated sugars, NTP/NDP and cation exchange transporters. However, our data also highlight the presence of diatom-specific transporter functions, such as carbon and amino acid transporters implicated in intricate plastid-mitochondria crosstalk events. These confirm previous observations that substrate non-specific triose phosphate transporters (TPT) may exist as principal transporters of phosphorylated sugars into and out of the diatom plastid, alongside suggesting probable agents of NTP exchange. Carbon and amino acid transport may be related to intricate metabolic plastid-mitochondria crosstalk. We additionally provide evidence from environmental meta-transcriptomic/meta- genomic data that plastid transporters may underpin diatom sensitivity to ocean warming, and identify a diatom plastid transporter (J43171) whose expression may be positively correlated with temperature.

Impaired photoprotection in Phaeodactylum tricornutum KEA3 mutants reveals the proton regulatory circuit of diatoms light acclimation

Diatoms are successful phytoplankton clades able to acclimate to changing environmental conditions, including e.g. variable light intensity. Diatoms are outstanding at dissipating light energy exceeding the maximum photosynthetic electron transfer (PET) capacity via the nonphotochemical quenching (NPQ) process. While the molecular effectors of NPQ as well as the involvement of the proton motive force (PMF) in its regulation are known, the regulators of the PET/PMF relationship remain unidentified in diatoms. We generated mutants of the H⁺ /K⁺ antiporter KEA3 in the model diatom Phaeodactylum tricornutum. Loss of KEA3 activity affects the PET/PMF coupling and NPQ responses at the onset of illumination, during transients and in steady-state conditions. Thus, this antiporter is a main regulator of the PET/PMF coupling. Consistent with this conclusion, a parsimonious model including only two free components, KEA3 and the diadinoxanthin de-epoxidase, describes most of the feedback loops between PET and NPQ. This simple regulatory system allows for efficient responses to fast (minutes) or slow (e.g. diel) changes in light environment, thanks to the presence of a regulatory calcium ion (Ca²⁺ )-binding domain in KEA3 modulating its activity. This circuit is likely tuned by the NPQ-effector proteins, LHCXs, providing diatoms with the required flexibility to thrive in different ocean provinces.

Inactivation of mitochondrial complex I stimulates chloroplast ATPase in Physcomitrium patens

Light is the ultimate source of energy for photosynthetic organisms, but respiration is fundamental for supporting metabolism during the night or in heterotrophic tissues. In this work, we isolated Physcomitrella (Physcomitrium patens) plants with altered respiration by inactivating Complex I (CI) of the mitochondrial electron transport chain by independently targeting on two essential subunits. Inactivation of CI caused a strong growth impairment even in fully autotrophic conditions in tissues where all cells are photosynthetically active, demonstrating that respiration is essential for photosynthesis. CI mutants showed alterations in the stoichiometry of respiratory complexes while the composition of photosynthetic apparatus was substantially unaffected. CI mutants showed altered photosynthesis with high activity of both Photosystems I and II, likely the result of high chloroplast ATPase activity that led to smaller ΔpH formation across thylakoid membranes, decreasing photosynthetic control on cytochrome b6f in CI mutants. These results demonstrate that alteration of respiratory activity directly impacts photosynthesis in P. patens and that metabolic interaction between organelles is essential in their ability to use light energy for growth.

Consequences of Mixotrophy on Cell Energetic Metabolism in Microchloropsis gaditana Revealed by Genetic Engineering and Metabolic Approaches

Algae belonging to the Microchloropsis genus are promising organisms for biotech purposes, being able to accumulate large amounts of lipid reserves. These organisms adapt to different trophic conditions, thriving in strict photoautotrophic conditions, as well as in the concomitant presence of light plus reduced external carbon as energy sources (mixotrophy). In this work, we investigated the mixotrophic responses of Microchloropsis gaditana (formerly Nannochloropsis gaditana). Using the Biolog growth test, in which cells are loaded into multiwell plates coated with different organic compounds, we could not find a suitable substrate for Microchloropsis mixotrophy. By contrast, addition of the Lysogeny broth (LB) to the inorganic growth medium had a benefit on growth, enhancing respiratory activity at the expense of photosynthetic performances. To further dissect the role of respiration in Microchloropsis mixotrophy, we focused on the mitochondrial alternative oxidase (AOX), a protein involved in energy management in other algae prospering in mixotrophy. Knocking-out the AOX1 gene by transcription activator-like effector nuclease (TALE-N) led to the loss of capacity to implement growth upon addition of LB supporting the hypothesis that the effect of this medium was related to a provision of reduced carbon. We conclude that mixotrophic growth in Microchloropsis is dominated by respiratory rather than by photosynthetic energetic metabolism and discuss the possible reasons for this behavior in relationship with fatty acid breakdown via β-oxidation in this oleaginous alga.

Regulation of electron transport is essential for photosystem I stability and plant growth

Photosynthetic electron transport is regulated by cyclic and pseudocyclic electron flow (CEF and PCEF) to maintain the balance between light availability and metabolic demands. CEF transfers electrons from photosystem I to the plastoquinone pool with two mechanisms, dependent either on PGR5/PGRL1 or on the type I NADH dehydrogenase-like (NDH) complex. PCEF uses electrons from photosystem I to reduce oxygen and in many groups of photosynthetic organisms, but remarkably not in angiosperms, it is catalyzed by flavodiiron proteins (FLVs). In this study, Physcomitrella patens plants depleted in PGRL1, NDH and FLVs in different combinations were generated and characterized, showing that all these mechanisms are active in this moss. Surprisingly, in contrast to flowering plants, Physcomitrella patens can cope with the simultaneous inactivation of PGR5- and NDH-dependent CEF but, when FLVs are also depleted, plants show strong growth reduction and photosynthetic activity is drastically reduced. The results demonstrate that mechanisms for modulation of photosynthetic electron transport have large functional overlap but are together indispensable to protect photosystem I from damage and they are an essential component for photosynthesis in any light regime.

The chloroplast NADH dehydrogenase-like complex influences the photosynthetic activity of the moss Physcomitrella patens

Alternative electron pathways contribute to regulation of photosynthetic light reactions to adjust to metabolic demands in dynamic environments. The chloroplast NADH dehydrogenase-like (NDH) complex mediates the cyclic electron transport pathway around PSI in different cyanobacteria, algae, and plant species, but it is not fully conserved in all photosynthetic organisms. In order to assess how the physiological role of this complex changed during plant evolution, we isolated Physcomitrella patens lines knocked out for the NDHM gene that encodes a subunit fundamental for the activity of the complex. ndhm knockout mosses indicated high PSI acceptor side limitation upon abrupt changes in illumination. In P. patens, pseudo-cyclic electron transport mediated by flavodiiron proteins (FLVs) was also shown to prevent PSI over-reduction in plants exposed to light fluctuations. flva ndhm double knockout mosses had altered photosynthetic performance and growth defects under fluctuating light compared with the wild type and single knockout mutants. The results showed that while the contribution of NDH to electron transport is minor compared with FLV, NDH still participates in modulating photosynthetic activity, and it is critical to avoid PSI photoinhibition, especially when FLVs are inactive. The functional overlap between NDH- and FLV-dependent electron transport supports PSI activity and prevents its photoinhibition under light variations.

Role of cyclic and pseudo-cyclic electron transport in response to dynamic light changes in Physcomitrella patens

Photosynthetic organisms support cell metabolism by harvesting sunlight and driving the electron transport chain at the level of thylakoid membranes. Excitation energy and electron flow in the photosynthetic apparatus is continuously modulated in response to dynamic environmental conditions. Alternative electron flow around photosystem I plays a seminal role in this regulation contributing to photoprotection by mitigating overreduction of the electron carriers. Different pathways of alternative electron flow coexist in the moss Physcomitrella patens, including cyclic electron flow mediated by the PGRL1/PGR5 complex and pseudo-cyclic electron flow mediated by the flavodiiron proteins FLV. In this work, we generated P. patens plants carrying both pgrl1 and flva knock-out mutations. A comparative analysis of the WT, pgrl1, flva, and pgrl1 flva lines suggests that cyclic and pseudo-cyclic processes have a synergic role in the regulation of photosynthetic electron transport. However, although both contribute to photosystem I protection from overreduction by modulating electron flow following changes in environmental conditions, FLV activity is particularly relevant in the first seconds after a light change whereas PGRL1 has a major role upon sustained strong illumination.

Balancing protection and efficiency in the regulation of photosynthetic electron transport across plant evolution

Contents Summary 105 I. Introduction 105 II. Diversity of molecular mechanisms for regulation of photosynthetic electron transport 106 III. Role of FLVs in the regulation of photosynthesis in eukaryotes 107 IV. Why were FLVs lost in angiosperms? 108 V. Conclusions 108 Acknowledgements 109 References 109 SUMMARY: Photosynthetic electron transport requires continuous modulation to maintain the balance between light availability and metabolic demands. Multiple mechanisms for the regulation of electron transport have been identified and are unevenly distributed among photosynthetic organisms. Flavodiiron proteins (FLVs) influence photosynthetic electron transport by accepting electrons downstream of photosystem I to reduce oxygen to water. FLV activity has been demonstrated in cyanobacteria, green algae and mosses to be important in avoiding photosystem I overreduction upon changes in light intensity. FLV-encoding sequences were nevertheless lost during evolution by angiosperms, suggesting that these plants increased the efficiency of other mechanisms capable of accepting electrons from photosystem I, making the FLV activity for protection from overreduction superfluous or even detrimental for photosynthetic efficiency.

Systemic Calcium Wave Propagation in Physcomitrella patens

The adaptation to dehydration and rehydration cycles represents a key step in the evolution of photosynthetic organisms and requires the development of mechanisms by which to sense external stimuli and translate them into signaling components. In this study, we used genetically encoded fluorescent sensors to detect specific transient increases in the Ca2+ concentration in the moss Physcomitrella patens upon dehydration and rehydration treatment. Observation of the entire plant in a single time-series acquisition revealed that various cell types exhibited different sensitivities to osmotic stress and that Ca2+ waves originated from the basal part of the gametophore and were directionally propagated towards the top of the plant. Under similar conditions, the vascular plant Arabidopsis thaliana exhibited Ca2+ waves that propagated at a higher speed than those of P. patens. Our results suggest that systemic Ca2+ propagation occurs in plants even in the absence of vascular tissue, even though the rates can be different.

IV Valproate in generalized convulsive status epilepticus: a systematic review

Aim of this review was to evaluate efficacy and safety of intravenous valproate (IV VPA) in the treatment of generalized convulsive status epilepticus (GCSE) in patients of any age, synthesizing available evidences from randomized controlled trials (RCTs). RCTs on IV VPA administered in patients (no age restriction) for GCSE at any stage were searched in MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials. Studies were selected and data independently extracted. Following outcomes were considered: clinical seizure cessation after drug administration, seizure freedom at 24 h, and adverse effects. Outcomes were assessed using standard methods to calculate risk ratio (RR) with 95% confidence intervals. Five trials met inclusion criteria. Two different comparisons were available (IV VPA versus phenytoin (PHT), IV VPA versus IV Diazepam), but only the former included more than one study with enough information to permit a meta-analysis. Compared with PHT, VPA had statistically lower risk of adverse effects (RR 0.31, 95% CI 0.12-0.85), with no differences in GCSE cessation after drug administration (RR 1.31, 95% CI 0.93-1.84) and in seizure freedom at 24 h (RR 0.96, 95% CI 0.88-1.06). This review suggests that IV VPA has a better tolerability than PHT in treatment of GCSE, without any statistically significant differences in terms of efficacy. More rigorous RCTs of VPA versus an appropriate comparator, in a well-defined population with a systematic definition of SE, are however required to conclude about efficacy and tolerability of VPA in clinical practice.

[Does the use of a polyurethane patch in the CVC dressing further reduce the risk of infection compared with sterile gauze dressing?]

Half of the patients hospitalized in intensive care units have a central venous catheter (CVC) inserted. Management of CVC is not simple and the wrong medication on the insertion site may cause many complications including sepsis. Among the various modes of dressing are transparent polyurethane patches and sterile gauze, and both have both advantages and drawbacks. The aim of this literature review is to compare these two methods in terms of effectiveness in reducing infections. Seven bio-medical databases of the primary and secondary literature were consulted. We considered all articles published in the last five years, in Italian or English, and research that studies purely human subjects. Moreover, the work was limited to all RCT, all systematic reviews and guidelines published on the databases consulted. Only five studies tackled the research question. The results show that CVC-related infections are a frequent problem in intensive care units. This research found two systematic reviews and two randomized controlled trials. None of the studies show any evidence of the type of dressing applied to the CVC. In conclusion, despite consulting several databases, we found no evidence recommending the type of medication to apply.

Comparison of two protocols of conscious analgosedation in video-assisted talc pleurodesis

AIM

Video-assisted thoracoscopy surgery (VATS) is classically performed using general anesthesia with a double-lumen endotracheal tube to allow collapse of the operated lung. However, according to our opinion, the risks of general anesthesia with one-lung ventilation could be accepted when major thoracic operation is planned, but it should be avoided or kept at minimum when performing less invasive procedures such as video-assisted talc pleurodesis. In this paper, 2 different protocols are described in order to demonstrate the effectiveness and safety of Monitored Anesthesia Care (MAC) for performing VATS talc pleurodesis.

METHODS

We studied 65 neoplastic patients ASA III-IV who underwent video-assisted pleurodesis with talc nebulization. They were randomized into 2 homogenous groups: Group 1, received midazolam (0.015-0.030 mg/kg) and sufentanil (0.15-0.20 microg/kg); Group 2, received midazolam (0.15-0.2 mg/kg) and continuous remifentanil infusion 0.5-1 microg/kg/min in the first minute, followed by 0.05 microg/kg/min. Local anesthesia with 0.2% ropivacaine was employed before the thoracoscopic trocar was inserted in both groups. Intraoperative standard monitoring required ECG, heart rate, non-invasive blood pressure, transcutaneous carbon dioxide and oxygen saturation. Consciousness status has been evaluated by Ramsey scale, while pain intensity by VAS scale.

RESULTS

No statistically significant fluctuations were observed for mean arterial pressure, heart rate, SpO(2), tCO(2), VAS and Ramsey score. No postoperative complications and hospital mortality occurred.

CONCLUSIONS

Both the protocols offer an efficient control of analgosedation with a minimum incidence of intraoperative and postoperative side effects. Anyway, the titration of the drug is very important.

Effects of short-term lithium treatment on peripheral blood lymphocytes and granulocytes in healthy volunteers

The effects of a short-term treatment with lithium carbonate on lymphocytes and granulocytes were studied in six normal subjects. The lithium effects are related to a direct, immediate and quickly reversible action of the drug on the bone marrow, as demonstrated by the granulocyte number and variations in Arneth's index. Although lymphocyte and granulocyte functions do not seem to be affected by lithium when investigated by the usual methods, the ability of the drug to counteract the theophylline-induced inhibition of cellular functions would suggest that lithium acts mainly through the modulation of intracellular levels of cyclic nucleotides. This is confirmed by evaluation of cellular cyclic 3',5'-adenosine monophosphate (cAMP). The above hypothesis could explain the quick onset and loss of lithium action on granulopoiesis.