dark-to-light transition
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Our circadian world shapes much of metabolic physiology. In mice ∼40% of the light and ∼80% of the dark phase time is characterized by bouts of increased energy expenditure (EE). These ultradian bouts have a higher body temperature (Tb) and thermal conductance and contain virtually all of the physical activity and awake time. Bout status is a better classifier of mouse physiology than photoperiod, with ultradian bouts superimposed on top of the circadian light/dark cycle. We suggest that the primary driver of ultradian bouts is a brain-initiated transition to a higher defended Tb of the active/awake state. Increased energy expenditure from brown adipose tissue, physical activity, and cardiac work combine to raise Tb from the lower defended Tb of the resting/sleeping state. Thus, unlike humans, much of mouse metabolic physiology is episodic with large ultradian increases in EE and Tb that correlate with the active/awake state and are poorly aligned with circadian cycling.
- MeSH
- bdění fyziologie MeSH
- cirkadiánní rytmus * fyziologie MeSH
- energetický metabolismus * fyziologie MeSH
- fotoperioda * MeSH
- hnědá tuková tkáň metabolismus fyziologie MeSH
- myši MeSH
- spánek fyziologie MeSH
- tělesná teplota * fyziologie MeSH
- ultradiánní rytmus * fyziologie MeSH
- zvířata MeSH
- Check Tag
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
The transition from vegetative to reproductive phases is the most fundamental and tightly controlled switch in the life of flowering plants. The short-day plant Chenopodium rubrum is a fast cycling annual plant lacking a juvenile phase. It can be induced to flowering at the seedling stage by exposure to a single period of darkness. This floral induction may then be cancelled by a short pulse of red light at midnight called night break (NB), which also inhibits the floral activator FLOWERING LOCUS T LIKE 1 (CrFTL1). We performed a comparative transcriptomic study between C. rubrum seedlings treated by NB and ones growing through uninterrupted night, and found about six hundred differentially expressed genes, including the B-BOX DOMAIN (BBX) genes. We focused on the CrBBX19 and BOLTING TIME CONTROL 1 (BTC1) genes, homologous to the upstream regulators of the BvFT2, a floral inducer in sugar beet. The transcription patterns of the two genes were compatible with their putative role as a sensor of the dark period length optimal for flowering (CrBBX19), and a signal of lights-on (CrBTC1), but the participation of other genes cannot be excluded. The expression profiles of CrBBX19 and the homolog of the core endogenous clock gene LATE ELONGATED HYPOCOTYL (LHY) were highly similar, which suggested their co-regulation.
BACKGROUND: With limited agricultural land and increasing human population, it is essential to enhance overall photosynthesis and thus productivity. Oxygenic photosynthesis begins with light absorption, followed by excitation energy transfer to the reaction centres, primary photochemistry, electron and proton transport, NADPH and ATP synthesis, and then CO2 fixation (Calvin-Benson cycle, as well as Hatch-Slack cycle). Here we cover some of the discoveries related to this process, such as the existence of two light reactions and two photosystems connected by an electron transport 'chain' (the Z-scheme), chemiosmotic hypothesis for ATP synthesis, water oxidation clock for oxygen evolution, steps for carbon fixation, and finally the diverse mechanisms of regulatory processes, such as 'state transitions' and 'non-photochemical quenching' of the excited state of chlorophyll a. SCOPE: In this review, we emphasize that mathematical modelling is a highly valuable tool in understanding and making predictions regarding photosynthesis. Different mathematical models have been used to examine current theories on diverse photosynthetic processes; these have been validated through simulation(s) of available experimental data, such as chlorophyll a fluorescence induction, measured with fluorometers using continuous (or modulated) exciting light, and absorbance changes at 820 nm (ΔA820) related to redox changes in P700, the reaction centre of photosystem I. CONCLUSIONS: We highlight here the important role of modelling in deciphering and untangling complex photosynthesis processes taking place simultaneously, as well as in predicting possible ways to obtain higher biomass and productivity in plants, algae and cyanobacteria.
- MeSH
- biomasa MeSH
- chlorofyl a * MeSH
- chlorofyl MeSH
- fotosyntéza * MeSH
- fotosystém II (proteinový komplex) MeSH
- kyslík MeSH
- lidé MeSH
- světlo MeSH
- transport elektronů MeSH
- voda MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- přehledy MeSH
Cyanobacteria are known for their ability to produce and release mixtures of up to thousands of compounds into the environment. Recently, the production of novel metabolites, retinoids, was reported for some cyanobacterial species along with teratogenic effects of samples containing these compounds. Retinoids are natural endogenous substances derived from vitamin A that play a crucial role in early vertebrate development. Disruption of retinoid signalling- especially during the early development of the nervous system- might lead to major malfunctions and malformations. In this study, the toxicity of cyanobacterial biomass samples from the field containing retinoids was characterized by in vivo and in vitro bioassays with a focus on the potential hazards towards nervous system development and function. Additionally, in order to identify the compounds responsible for the observed in vitro and in vivo effects the complex cyanobacterial extracts were fractionated (C18 column, water-methanol gradient) and the twelve obtained fractions were tested in bioassays. In all bioassays, all-trans retinoic acid (ATRA) was tested along with the environmental samples as a positive control. Retinoid-like activity (mediated via the retinoic acid receptor, RAR) was measured in the transgenic cell line p19/A15. The in vitro assay showed retinoid-like activity by specific interaction with RAR for the biomass samples. Neurotoxic effects of selected samples were studied on zebrafish (Danio rerio) embryos using the light/dark transition test (Viewpoint, ZebraLab system) with 120 hpf larvae. In the behavioural assay, the cyanobacterial extracts caused significant hyperactivity in zebrafish at 120 hpf after acute exposure (3 h prior to the measurement) at concentrations below the teratogenicity LOEC (0.2 g dw L-1). Similar effect was observed after exposure to fractions of the extracts with detected retinoid-like activity and additive effect was observed after combining the fractions. However, the effect on behaviour was not observed after exposure to ATRA only. To provide additional insight into the behavioural effects and describe the underlying mechanism gene expression of selected biomarkers was measured. We evaluated an array of 28 genes related to general toxicity, neurodevelopment, retinoid and thyroid signalling. We detected several affected genes, most notably, the Cyp26 enzymes that control endogenous ATRA concentration, which documents an effect on retinoid signalling.
- MeSH
- biomasa MeSH
- biotest MeSH
- chemické látky znečišťující vodu metabolismus toxicita MeSH
- chování zvířat účinky léků MeSH
- dánio pruhované růst a vývoj metabolismus MeSH
- embryo nesavčí účinky léků metabolismus MeSH
- exprese genu účinky léků MeSH
- myši MeSH
- nádorové buněčné linie MeSH
- receptory kyseliny retinové genetika metabolismus MeSH
- sinice růst a vývoj metabolismus MeSH
- tretinoin metabolismus toxicita MeSH
- zvířata MeSH
- Check Tag
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
Chlorophyll fluorescence kinetic analysis has become an important tool in basic and applied research on plant physiology and agronomy. While early systems recorded the integrated kinetics of a selected spot or plant, later systems enabled imaging of at least the slower parts of the kinetics (20-ms time resolution). For faster events, such as the rise from the basic dark-adapted fluorescence yield to the maximum (OJIP transient), or the fluorescence yield decrease during reoxidation of plastoquinone A after a saturating flash, integrative systems are used because of limiting speed of the available imaging systems. In our new macroscopic and microscopic systems, the OJIP or plastonique A reoxidation fluorescence transients are directly imaged using an ultrafast camera. The advantage of such systems compared to nonimaging measurements is the analysis of heterogeneity of measured parameters, for example between the photosynthetic tissue near the veins and the tissue further away from the veins. Further, in contrast to the pump-and-probe measurement, direct imaging allows for measuring the transition of the plant from the dark-acclimated to a light-acclimated state via a quenching analysis protocol in which every supersaturating flash is coupled to a measurement of the fast fluorescence rise. We show that pump-and-probe measurement of OJIP is prone to artifacts, which are eliminated with the direct measurement. The examples of applications shown here, zinc deficiency and cadmium toxicity, demonstrate that this novel imaging platform can be used for detection and analysis of a range of alterations of the electron flow around PSII.
- MeSH
- Arabidopsis cytologie metabolismus MeSH
- Brassicaceae cytologie účinky léků metabolismus MeSH
- chlorofyl chemie metabolismus MeSH
- design vybavení MeSH
- fluorescence MeSH
- fluorescenční mikroskopie přístrojové vybavení metody MeSH
- fotosyntéza MeSH
- Glycine max cytologie účinky léků metabolismus MeSH
- kinetika MeSH
- listy rostlin cytologie MeSH
- mezofylové buňky metabolismus MeSH
- plastochinon metabolismus MeSH
- zinek metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
MAIN CONCLUSION: The absence of state transitions in a Nt(Hn) cybrid is due to a cleavage of the threonine residue from the misprocessed N-terminus of the LHCII polypeptides. The cooperation between the nucleus and chloroplast genomes is essential for plant photosynthetic fitness. The rapid and specific interactions between nucleus-encoded and chloroplast-encoded proteins are under intense investigation with potential for applications in agriculture and renewable energy technology. Here, we present a novel model for photosynthesis research in which alien henbane (Hyoscyamus niger) chloroplasts function on the nuclear background of a tobacco (Nicotiana tabacum). The result of this coupling is a cytoplasmic hybrid (cybrid) with inhibited state transitions-a mechanism responsible for balancing energy absorption between photosystems. Protein analysis showed differences in the LHCII composition of the cybrid plants. SDS-PAGE analysis revealed a novel banding pattern in the cybrids with at least one additional 'LHCII' band compared to the wild-type parental species. Proteomic work suggested that the N-terminus of at least some of the cybrid Lhcb proteins was missing. These findings provide a mechanistic explanation for the lack of state transitions-the N-terminal truncation of the Lhcb proteins in the cybrid included the threonine residue that is phosphorylated/dephosphorylated in order to trigger state transitions and therefore crucial energy balancing mechanism in plants.
- MeSH
- buněčné jádro metabolismus MeSH
- chloroplasty metabolismus MeSH
- fosforylace MeSH
- fotosyntéza MeSH
- fotosystém II (proteinový komplex) genetika metabolismus MeSH
- genom chloroplastový genetika MeSH
- genom rostlinný genetika MeSH
- proteomika MeSH
- světlosběrné proteinové komplexy genetika metabolismus MeSH
- tabák genetika fyziologie MeSH
- threonin metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
Arctic microalgae experience long periods of continuous darkness during the polar night, when they are unable to photosynthesize. Despite numerous studies on overwintering strategies, such as utilization of stored energy products, formation of resting stages, reduction of metabolic rates and heterotrophic lifestyles, there have been few attempts to assess the in situ physiological state and restoration of the photosynthetic apparatus upon re-illumination. In this study, we found diverse and active marine phytoplankton communities during the polar night at 78°N. Furthermore, we observed rapid changes (≤20 min) in the efficiency of photosynthetic electron transport upon re-illumination. High photosynthetic capacity and net primary production were established after 24 h of re-illumination. Our results suggest that some Arctic autotrophs maintain fully functional photosystem II and downstream electron acceptors during the polar night even though the low in situ net primary production levels measured in January prove that light was not sufficient to support any measurable primary production. Due to low temperatures resulting in low respiratory rates as well as the absence of photodamage during the polar night, maintenance of basic photosynthetic machinery may actually pose relatively low metabolic costs for algal cells. This could allow Arctic microalgae to endure the polar night without the formation of dormant stages, enabling them to recover and take advantage of light immediately upon the suns return during the winter-spring transition.
- MeSH
- bílkoviny řas metabolismus MeSH
- fotosyntéza fyziologie MeSH
- fotosystém II (proteinový komplex) metabolismus MeSH
- fytoplankton fyziologie MeSH
- mikrořasy fyziologie MeSH
- roční období MeSH
- tma * MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Arktida MeSH
- Svalbard MeSH
Photosystem II (PSII) catalyses the photoinduced oxygen evolution and, by producing reducing equivalents drives, in concert with PSI, the conversion of carbon dioxide to sugars. Our knowledge about the architecture of the reaction centre (RC) complex and the mechanisms of charge separation and stabilisation is well advanced. However, our understanding of the processes associated with the functioning of RC is incomplete: the photochemical activity of PSII is routinely monitored by chlorophyll-a fluorescence induction but the presently available data are not free of controversy. In this work, we examined the nature of gradual fluorescence rise of PSII elicited by trains of single-turnover saturating flashes (STSFs) in the presence of a PSII inhibitor, permitting only one stable charge separation. We show that a substantial part of the fluorescence rise originates from light-induced processes that occur after the stabilisation of charge separation, induced by the first STSF; the temperature-dependent relaxation characteristics suggest the involvement of conformational changes in the additional rise. In experiments using double flashes with variable waiting times (∆τ) between them, we found that no rise could be induced with zero or short ∆τ, the value of which depended on the temperature - revealing a previously unknown rate-limiting step in PSII.
- MeSH
- chlorofyl a metabolismus MeSH
- fluorescence * MeSH
- fotosyntéza MeSH
- fotosystém II (proteinový komplex) antagonisté a inhibitory metabolismus MeSH
- Spinacia oleracea metabolismus MeSH
- Synechococcus metabolismus MeSH
- Synechocystis metabolismus MeSH
- teplota MeSH
- tylakoidy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Photo-reduction of O2to water mediated by flavodiiron proteins (FDPs) represents a safety valve for the photosynthetic electron transport chain in fluctuating light. So far, the FDP-mediated O2photo-reduction has been evidenced only in cyanobacteria and the moss Physcomitrella; however, a recent phylogenetic analysis of transcriptomes of photosynthetic organisms has also revealed the presence of FDP genes in several nonflowering plant groups. What remains to be clarified is whether the FDP-dependent O2photo-reduction is actually operational in these organisms. We have established a simple method for the monitoring of FDP-mediated O2photo-reduction, based on the measurement of redox kinetics of P700 (the electron donor of photosystem I) upon dark-to-light transition. The O2photo-reduction is manifested as a fast re-oxidation of P700. The validity of the method was verified by experiments with transgenic organisms, namely FDP knock-out mutants of Synechocystis and Physcomitrella and transgenic Arabidopsis plants expressing FDPs from Physcomitrella. We observed the fast P700 re-oxidation in representatives of all green plant groups excluding angiosperms. Our results provide strong evidence that the FDP-mediated O2photo-reduction is functional in all nonflowering green plant groups. This finding suggests a major change in the strategy of photosynthetic regulation during the evolution of angiosperms.
Aggregation induced conformational change of light harvesting antenna complexes is believed to constitute one of the pathways through which photosynthetic organisms can safely dissipate the surplus of energy while exposed to saturating light. In this study, Stark fluorescence (SF) spectroscopy is applied to minor antenna complexes (CP24, CP26 and CP29) both in their light-harvesting and energy-dissipating states to trace and characterize different species generated upon energy dissipation through aggregation (in-vitro) induced conformational change. SF spectroscopy could identify three spectral species in the dissipative state of CP24, two in CP26 and only one in CP29. The comprehensive analysis of the SF spectra yielded different sets of molecular parameters for the multiple spectral species identified in CP24 or CP26, indicating the involvement of different pigments in their formation. Interestingly, a species giving emission around the 730nm spectral region is found to form in both CP24 and CP26 following transition to the energy dissipative state, but not in CP29. The SF analyses revealed that the far red species has exceptionally large charge transfer (CT) character in the excited state. Moreover, the far red species was found to be formed invariably in both Zeaxanthin (Z)- and Violaxathin (V)-enriched CP24 and CP26 antennas with identical CT character but with larger emission yield in Z-enriched ones. This suggests that the carotenoid Z is not directly involved but only confers an allosteric effect on the formation of the far red species. Similar far red species with remarkably large CT character were also observed in the dissipative state of the major light harvesting antenna (LHCII) of plants [Wahadoszamen et al. PCCP, 2012], the fucoxanthin-chlorophyll protein (FCP) of brown algae [Wahadoszamen et al. BBA, 2014] and cyanobacterial IsiA [Wahadoszamen et al. BBA, 2015], thus pointing to identical sites and pigments active in the formation of the far red quenching species in different organisms.
- MeSH
- chlorofyl metabolismus účinky záření MeSH
- druhová specificita MeSH
- fluorescenční spektrometrie MeSH
- fotosyntéza * účinky záření MeSH
- konformace proteinů MeSH
- přenos energie MeSH
- Spinacia oleracea chemie metabolismus účinky záření MeSH
- světlo MeSH
- světlosběrné proteinové komplexy chemie metabolismus účinky záření MeSH
- vztahy mezi strukturou a aktivitou MeSH
- xanthofyly metabolismus MeSH
- zeaxanthiny metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
