Prolonged Darkness Research Articles

Survival of Prochlorococcus in extended darkness

AbstractProchlorococcus is the smallest oxygenic phototroph in the ocean, where it can be found in great abundance throughout the euphotic zone in mid‐latitude waters. Populations of this picocyanobacterium have been observed below the euphotic zone, but the viability of these cells is unclear. To explore the tolerance of Prochlorococcus to extended light‐deprivation, we subjected multiple strains of Prochlorococcus to varying periods of darkness and examined their ability to recover when placed back in the light. Some strains recovered after 35 h of darkness while others could not; this variability was not related to whether the strains were members of high‐ or low‐ light adapted ecotypes. The presence of a marine heterotroph, Alteromonas macleodii MIT1002, in the cultures extended their ability to survive prolonged darkness, in the most extreme case by 11 d. This could be attributed at least in part to the reduction of hydrogen peroxide in co‐cultures, consistent with known roles of “helper bacteria” in detoxifying hydrogen peroxide, and this effect could be mimicked to some degree by the addition of a known hydrogen peroxide quencher, sodium pyruvate. The addition of glucose alone to the cultures provided marginal enhancement, but when both pyruvate and glucose were added together, all strains were able to survive longer in darkness than they were with only the heterotroph added. Thus, it appears that Prochlorococcus dark‐survival depends on a multitude of factors. Limited analyses of Synechococcus suggest that its dark‐survival capacity is longer than that of Prochlorococcus, for reasons that are not yet clear.

Congenital stationary night blindness with hypoplastic discs, negative electroretinogram and thinning of the inner nuclear layer.

To describe congenital stationary night blindness (CSNB) with negative electroretinogram, hypoplastic discs, nystagmus and thinning of the inner nuclear layer (INL). Retinal structure was analyzed qualitatively with spectral domain optical coherence tomography and wide field imaging. Retinal function was evaluated with full-field electroretinography (ffERG). Molecular genetic testing included next-generation sequencing (NGS) of the known genes involved in CSNB. Patients presented with CSNB presented with nystagmus, high myopia, hypoplastic discs and negative ffERG with no measurable rod response. The retinas appeared normal and automated segmentation of retinal layers demonstrated a relative reduction of thickness of the INL. There was no significant change in the ffERG after prolonged 2hour dark adaptation compared to standard 30minute dark adaptation. Affected family members harboured the homozygous 1-bp deletion c.2394delC in exon 18 of the TRPM1 gene, whereas their unaffected parents were heterozygous carriers. This data expands the genotype and phenotype spectrum of CSNB. The lack of improvement of rod responses after prolonged dark adaptation, together with thinning of the INL, is compatible with postreceptoral transmission dysfunction in the bipolar cells. Such knowledge may prove useful in future development of treatment for outer retinal dystrophies, using opsin genes to restore light responses in survivor neurons in the inner retina.

Preserved visual function in retinal dystrophy due to hypomorphic RPE65 mutations

Background/aimsTo present detailed phenotypic and molecular findings in four patients from four families with atypical, mild, recessive RPE65-related retinal dystrophy and discuss potential implications for gene replacement therapy.MethodsFour patients from...

Systems Medicine of Cancer: Bringing Together Clinical Data and Nonlinear Dynamics of Genetic Networks

The last few years have witnessed major developments in experimental techniques for analysis of cancer, including full genome sequencing, measurement of multiple oncomarkers, DNA methylation profile, genomic profile, or transcriptome of the pathological tissue. Whilst these advances have provided some additional understanding of cancer onset and development, the problem of cancer is far from solved. Since the amounts of data emerging from these are very substantial, and the data itself can be extremely heterogeneous (qualitative, quantitative, and verbal descriptions), this makes standard data analysis techniques not practically applicable. One promising direction of addressing the problem of analysis of cancer data is to use modern and sophisticated methods from systems biology and cybernetics. Some challenges of this approach are connecting the results of mathematical analysis with real clinical data, and bridging the existing gaps between the communities of clinicians and applied mathematicians. This special issue showcases some of the most recent developments in the areas of nonlinear dynamics, mathematical analysis and modeling, data analysis, and simulations in the area of cancer. Having received 11 submissions, six best papers were chosen and published to provide an overview of the research field and to motivate further study. In “Optimal Placement of Irradiation Sources in the Planning of Radiotherapy: Mathematical Models and Methods of Solving,” O. Blyuss et al. analyse optimal choice of placement of irradiation sources during radiotherapy as an optimization problem. Using the techniques of nondifferentiable optimization and an approximate Klepper's algorithm, the authors derive a new approach for solving this problem and illustrate their methodology with actual numerical simulations of different scenarios. The paper “Time-Delayed Models of Gene Regulatory Networks” by K. Parmar et al. provide an overview of existing mathematical techniques applicable to modeling the dynamics of gene regulatory networks. The authors focus on the effects of transcriptional and translational time delays and demonstrate how stability of different steady states and the associated behavior change depending on system parameters and the time delays. They contrast the dynamics of the fast mRNA regime, as described by a reduced model, with the dynamics of the full system to illustrate possible differences in behaviour and to highlight the important role played by the time delays. H. Namazi and M. Kiminezhadmalale in their paper titled “Diagnosis of Lung Cancer by Fractal Analysis of Damaged DNA” discuss how DNA sequences emerging from patient blood plasma can be studied by analysing DNA walks. Comparing the features of DNA profiles for healthy individuals with those for lung cancer patients, the authors derive several predictive criteria for lung cancer based on Hurst exponents and fractal dimension. The circadian physiology, clock genes, and cell cycle may critically affect results of cancer chronotherapeutics; hence, investigation of gene regulatory networks controlling circadian rhythms is an irreplaceable part of systems medicine of cancer. R. Heussen and D. Whitmore study how the circadian clock is entrained by light, and they experimentally investigate whether there exists a threshold for this synchronization. Moreover, analysis of the constructed numerical model shows that stochastic effects are an essential feature of the circadian clock that provides an explanation of signal decay from the zebrafish cell lines in prolonged darkness. Some cancer types are especially dangerous because of the high progression rate, and malignant gliomas represent one of the most severe types of tumors. Modern medical approaches offer sophisticated treatment procedures, based on microsurgical tumor removal combined with radio- and chemotherapy. A success of these surgical resection depends on the clarity of intraoperative diagnostics of human gliomas, and the review of O. Tyurikova et al. surveys the wide diversity of modern diagnostic methods used in the course of glial tumor resections. Recent development in systems biology and medicine have enabled us to analyse and infer networks of interactions and to search for new network oncomarkers. S.-M. Wang et al. in their paper about the identification of dysregulated genes and pathways in clear cell renal cell carcinoma provide an example of this research direction. Using systematic tracking the dysregulated modules of reweighted protein-protein interaction networks they successfully identified dysregulated genes and pathways for this type of cancer, thus gaining insights into possible biological markers or targets for drug development. We hope that the readers will find the papers published in this special issue interesting, and this will encourage and foster further research on developing new and efficient techniques in systems biology and data analysis for predicting the onset and for monitoring the progression of cancer. Konstantin B. Blyuss Ranjit Manchanda Jurgen Kurths Ahmed Alsaedi Alexey Zaikin

NiFe]-hydrogenase is essential for cyanobacterium Synechocystis sp. PCC 6803 aerobic growth in the dark.

The cyanobacterium Synechocystis sp. PCC 6803 has a bidirectional [NiFe]-hydrogenase (Hox hydrogenase) which reversibly reduces protons to H2. This enzyme is composed of a hydrogenase domain and a diaphorase moiety, which is distinctly homologous to the NADH input module of mitochondrial respiratory Complex I. Hox hydrogenase physiological function is still unclear, since it is not required for Synechocystis fitness under standard growth conditions. We analyzed the phenotype under prolonged darkness of three Synechocystis knock-out strains, lacking either Hox hydrogenase (ΔHoxE-H) or one of the proteins responsible for the assembly of its NiFe active site (ΔHypA1 and ΔHypB1). We found that Hox hydrogenase is required for Synechocystis growth under this condition, regardless of the functional status of its catalytic site, suggesting an additional role beside hydrogen metabolism. Moreover, quantitative proteomic analyses revealed that the expression levels of several subunits of the respiratory NADPH/plastoquinone oxidoreductase (NDH-1) are reduced when Synechocystis is grown in the dark. Our findings suggest that the Hox hydrogenase could contribute to electron transport regulation when both photosynthetic and respiratory pathways are down-regulated, and provide a possible explanation for the close evolutionary relationship between mitochondrial respiratory Complex I and cyanobacterial [NiFe]-hydrogenases.

A subgroup of MATE transporter genes regulates hypocotyl cell elongation in Arabidopsis.

The growth of higher plants is under complex regulation to ensure the elaboration of developmental programmes under a changing environment. To dissect these regulatory circuits, we carried out genetic screens for Arabidopsis abnormal shoot (abs) mutants with altered shoot development. Here, we report the isolation of two dominant mutants, abs3-1D and abs4-1D, through activation tagging. Both mutants showed a 'bushy' loss of apical dominance phenotype. ABS3 and ABS4 code for two closely related putative Multidrug and Toxic Compound Extrusion (MATE) family of efflux transporters, respectively. ABS3 and ABS4, as well as two related MATE genes, ABS3-Like1 (ABS3L1) and ABS3L2, showed diverse tissue expression profiles but their gene products all localized to the late endosome/prevacuole (LE/PVC) compartment. The over-expression of these four genes individually led to the inhibition of hypocotyl cell elongation in the light. On the other hand, the quadruple knockout mutant (mateq) showed the opposite phenotype of an enhanced hypocotyl cell elongation in the light. Hypocotyl cell elongation and de-etiolation processes in the dark were also affected by the mutations of these genes. Exogenously applied sucrose attenuated the inhibition of hypocotyl elongation caused by abs3-1D and abs4-1D in the dark, and enhanced the hypocotyl elongation of mateq under prolonged dark treatment. We determined that ABS3 genetically interacts with the photoreceptor gene PHYTOCHROME B (PHYB). Our results demonstrate that ABS3 and related MATE family transporters are potential negative regulators of hypocotyl cell elongation and support a functional link between the endomembrane system, particularly the LE/PVC, and the regulation of plant cell elongation.

The Impact of the Branched-Chain Ketoacid Dehydrogenase Complex on Amino Acid Homeostasis in Arabidopsis.

The branched-chain amino acids (BCAAs) Leu, Ile, and Val are among nine essential amino acids that must be obtained from the diet of humans and other animals, and can be nutritionally limiting in plant foods. Despite genetic evidence of its importance in regulating seed amino acid levels, the full BCAA catabolic network is not completely understood in plants, and limited information is available regarding its regulation. In this study, transcript coexpression analyses revealed positive correlations among BCAA catabolism genes in stress, development, diurnal/circadian, and light data sets. A core subset of BCAA catabolism genes, including those encoding putative branched-chain ketoacid dehydrogenase subunits, is highly expressed during the night in plants on a diel cycle and in prolonged darkness. Mutants defective in these subunits accumulate higher levels of BCAAs in mature seeds, providing genetic evidence for their function in BCAA catabolism. In addition, prolonged dark treatment caused the mutants to undergo senescence early and overaccumulate leaf BCAAs. These results extend the previous evidence that BCAAs can be catabolized and serve as respiratory substrates at multiple steps. Moreover, comparison of amino acid profiles between mature seeds and dark-treated leaves revealed differences in amino acid accumulation when BCAA catabolism is perturbed. Together, these results demonstrate the consequences of blocking BCAA catabolism during both normal growth conditions and under energy-limited conditions.

Improvement of retinal function in L-ORD after prolonged dark adaptation

ObjectiveTo describe the changes in dark-adapted (DA) retinal electrophysiological function after prolonged dark adaptation in a cohort of patients with late-onset retinal degeneration (L-ORD). DesignProspective case series. ParticipantsNine patients with either stage 2 or 3 L-ORD. MethodsInternational Society for Clinical Electrophysiology of Vision standard DA electroretinograms (ERGs) were performed before and after a period of extended dark adaptation (16 hours) in a cohort of patients heterozygous for the Ser163Arg mutation in C1QTNF5. ResultsRod function was abnormal in 8 of 9 patients after standard (20 min) of dark adaptation. After extended dark adaptation, rod function normalized in 4 patients and there was a mean improvement in the DA 0.01 rod-specific ERG b-wave amplitude of 310% (p = 0.004). A significant improvement in DA 3.0 a-wave ERG amplitude localized the improvement in rod function at the level of the photoreceptor. ConclusionsThis study demonstrates that a significant proportion of rod dysfunction in L-ORD can be reversed by extended dark adaptation and suggests that an abnormality of the visual cycle contributes to the pathogenesis of the disease. These findings would suggest that some retinal function could be restored, even in advanced cases of the disease if a suitable treatment is found.

Modelling the quality of potted plants after dark storage

Prolonged dark storage affects the quality of potted plants. A model was designed to quantify the effect of storage time and temperature on the display life of potted plants, such that logistics can be optimized, resulting in increased remaining quality and less rejected plants. Experiments were carried out with two Phalaenopsis cultivars, two Anthurium cultivars and two Cyclamen cultivars, the latter with two colour variants per cultivar. Plants were stored for different storage times at different temperatures. The aim of the chosen times and temperatures was to determine the quality effect of transport at optimal and suboptimal temperatures. After storage, plants were stored at 20°C for 14 days, for simulating a display period. Different quality aspects were scored immediately after storage and after 7 and 14 days of display.For each cultivar, a model was fitted consisting of a logistic function for representing the storage-time dependency of quality. In order to cope with both senescence symptoms at higher temperatures and chilling injury at lower temperatures, two non-interfering Arrhenius equations were incorporated. Because the effects of chilling exposure are commonly manifest only when the chilled plants are returned to ambient temperatures, the quality of Phalaenopsis and Anthurium plants measured immediately after storage at low temperatures was not taken into account. The behaviour of the Phalaenopsis and the Anthurium cultivars was well described by their models. The coefficients of determination based on the unexplained variation due to lack of fit were in the range of 0.89–0.99.

The greening after extended darkness1 is an N-end rule pathway mutant with high tolerance to submergence and starvation.

Plants respond to reductions in internal oxygen concentrations with adaptive mechanisms (for example, modifications of metabolism to cope with reduced supply of ATP). These responses are, at the transcriptional level, mediated by the group VII Ethylene Response Factor transcription factors, which have stability that is regulated by the N-end rule pathway of protein degradation. N-end rule pathway mutants are characterized by a constitutive expression of hypoxia response genes and abscisic acid hypersensitivity. Here, we identify a novel proteolysis6 (prt6) mutant allele, named greening after extended darkness1 (ged1), which was previously discovered in a screen for genomes uncoupled-like mutants and shows the ability to withstand long periods of darkness at the seedling stage. Interestingly, this ethyl methanesulfonate-derived mutant shows unusual chromosomal rearrangement instead of a point mutation. Furthermore, the sensitivity of N-end rule pathway mutants ged1 and prt6-1 to submergence was studied in more detail to understand previously contradicting experiments on this topic. Finally, it was shown that mutants for the N-end rule pathway are generally more tolerant to starvation conditions, such as prolonged darkness or submergence, which was partially associated with carbohydrate conservation.

Role of laccases and peroxidases in saprotrophic activities in the lichen Usnea undulata

Abstract Lichens produce various oxidoreductases including heme-containing peroxidases and the copper-containing phenol oxidases tyrosinase and laccase. Our earlier findings suggested that significant oxidoreductase activity occurs mainly in lichens from the order Peltigerales. Here we show that the non-Peltigeralean lichen Usnea can display significant activities of peroxidases and laccases. Strong evidence for the involvement of peroxidases and laccases in saprotrophic activities comes from the observation that their activities are induced by “starvation” due to prolonged dark storage, and also by treatment with soluble cellulose and lignin breakdown products. We also show that, given a quinone and chelated Fe, Usnea can produce hydroxyl radicals; these radicals contribute to the break down of carbohydrates or lignin. However, hydroxyl radical production is independent of laccase and peroxidase activity. Laccases and peroxidases are involved in other aspects of lichen biology; here we show that peroxidases, but not laccases, can break down lichen substances. Reduction in the amounts of lichen substances will reduce photoprotection, which will increase the photosynthetic capacity of thalli during winter when light intensities are low.

Expression of the BTB/POZ domain-containing protein At1g63850-like gene CsFDI1 is enhanced by sugar starvation in cucumber fruit

The cDNA of Cucumis sativus Fruit Defoliation Induced 1 (CsFDI1) was newly cloned using the subtraction method from a fruit of a defoliated cucumber (Cucumis sativus L. cv. Tokiwa) plant. An expression analysis of CsFDI1 in fruits and leaves was conducted along with those of the asparagine synthetase 1-like gene (AS) and Cucumis sativus Somatic Embryogenesis Zinc Finger 1 (CsSEF1), previously reported as control marker genes for sugar starvation. The transcript level of CsFDI1 and AS was relatively high, whereas that of CsSEF1 was very low under normal fruit development. The time course of the transcript levels of the three genes under prolonged darkness was compared with that of the fruit respiration rate and leaf starch concentration. The fruit respiration rate suggested that photoassimilate translocation to fruit ceased abruptly under prolonged darkness. The transcript level of CsFDI1, AS, and CsSEF1 increased in fruits, but the time course of the change was quite different in fruits and leaves under the condition of sugar starvation. The response of AS in leaves and CsSEF1 in fruits was close to all-or-none.

The Importance of Stochastic Effects for Explaining Entrainment in the Zebrafish Circadian Clock.

The circadian clock plays a pivotal role in modulating physiological processes and has been implicated, either directly or indirectly, in a range of pathological states including cancer. Here we investigate how the circadian clock is entrained by external cues such as light. Working with zebrafish cell lines and combining light pulse experiments with simulation efforts focused on the role of synchronization effects, we find that even very modest doses of light exposure are sufficient to trigger some entrainment, whereby a higher light intensity or duration correlates with strength of the circadian signal. Moreover, we observe in the simulations that stochastic effects may be considered an essential feature of the circadian clock in order to explain the circadian signal decay in prolonged darkness, as well as light initiated resynchronization as a strong component of entrainment.

Photosystem activity and state transitions of the photosynthetic apparatus in cyanobacterium Synechocystis PCC 6803 mutants with different redox state of the plastoquinone pool.

To better understand how photosystem (PS) activity is regulated during state transitions in cyanobacteria, we studied photosynthetic parameters of photosystem II (PSII) and photosystem I (PSI) in Synechocystis PCC 6803 wild type (WT) and its mutants deficient in oxidases (Ox(-)) or succinate dehydrogenase (SDH(-)). Dark-adapted Ox(-) mutant, lacking the oxidation agents, is expected to have a reduced PQ pool, while in SDH(-) mutant the PQ pool after dark adaptation will be more oxidized due to partial inhibition of the respiratory chain electron carriers. In this work, we tested the hypothesis that control of balance between linear and cyclic electron transport by the redox state of the PQ pool will affect PSII photosynthetic activity during state transition. We found that the PQ pool was reduced in Ox(-) mutant, but oxidized in SDH(-) mutant after prolonged dark adaptation, indicating different states of the photosynthetic apparatus in these mutants. Analysis of variable fluorescence and 77K fluorescence spectra revealed that the WT and SDH(-) mutant were in State 1 after dark adaptation, while the Ox(-) mutant was in State 2. State 2 was characterized by ~1.5 time lower photochemical activity of PSII, as well as high rate of P700 reduction and the low level of P700 oxidation, indicating high activity of cyclic electron transfer around PSI. Illumination with continuous light 1 (440nm) along with flashes of light 2 (620nm) allowed oxidation of the PQ pool in the Ox(-) mutant, thus promoting it to State 1, but it did not affect PSII activity in dark adapted WT and SDH(-) mutant. State 1 in the Ox(-) mutant was characterized by high variable fluorescence and P700(+) levels typical for WT and the SDH(-) mutant, indicating acceleration of linear electron transport. Thus, we show that PSII of cyanobacteria has a higher photosynthetic activity in State 1, while it is partially inactivated in State 2. This process is controlled by the redox state of PQ in cyanobacteria through enhancement/inhibition of electron transport on the acceptor side of PSII.

Effects of photoperiod on nutrient removal, biomass production, and algal-bacterial population dynamics in lab-scale photobioreactors treating municipal wastewater

Effects of photoperiod were investigated in lab-scale photobioreactors containing algal-bacterial consortia to reduce organic nutrients from municipal wastewater. Under three photoperiod conditions (12 h:12 h, 36 h:12 h, and 60 h:12 h dark–light cycles), nutrient removals and biomass productions were measured along with monitoring microbial population dynamics. After a batch operation for 12 days, 59–80% carbon, 35–88% nitrogen, and 43–89% phosphorus were removed from influents, respectively. In this study, carbon removal was related positively to the length of dark cycles, while nitrogen and phosphorus removals inversely. On the contrast, the highest microbial biomass in terms of chlorophyll a, dry cell weight, and algal/bacterial rRNA gene markers was produced under the 12 h:12 h dark–light cycle among the three photoperiods. The results showed 1) simultaneous growths between algae and bacteria in the microbial consortia and 2) efficient nitrogen and phosphorus removals along with high microbial biomass production under prolonged light conditions. Statistical analyses indicated that carbon removal was significantly related to the ratio of bacteria to algae in the microbial consortia along with prolonged dark conditions (p < 0.05). In addition, the ratio of nitrogen removal to phosphorus removal decreased significantly under prolonged dark conditions (p < 0.001). These results indicated that the photoperiod condition has remarkable impacts on adjusting nutrient removal, producing microbial biomass, and altering algal-bacterial population dynamics. Therefore, the control of photoperiod was suggested as an important operating parameter in the algal wastewater treatment.

The effect of light factor on the development of thallus and generative organs in Chara vulgaris L.

During long-term axenic culture of Chara continuous illumination (L=24) increases mitotic activity of almost all types of cells. In such conditions only initiation of oogonia is inhibited, leading into a strong predomination of male generative organs. Prolonged darkness (L:D=1:23) exerts a mitodepressing effect. Oogonia and antheridia are especially susceptible to the reduction of the light period. Modifications of the elongating growth in various photoperiods are different in the polyploid regions of the vegetative thallus and in haploid cells of the antheridial filaments. Segments of both axial internodes and lateral pleuridia increase their dimensions at L:D=1:23, whereas at L=24 their growth is significantly inhibited. Different reaction is noted in the cells of antheridial filaments: at L=24 they are about 10% longer than in the control (L:D=14:10). The duration of the antheridium aevelopment, from the stage of unicellular filaments to the moment of antheridium opening, is 1.5 days shorter at L=24 as compared with the control. This shortening includes proportionally both the period of divisions within antheridial filaments and the period of spermatozoid differentiation.

Leghaemoglobin Sub-Fractional Components in Chickpea Root Nodules during Extended Darkness

The aim of study was to investigate qualitative behavior of leghaemoglobin sub-fractional components during dark induced nodular senescence. A conventional protein purification method using ion exchange chromatography (HPLC) readily resolved ferric Lb into eight sub-fractional components namely a1, a2; b; c1, c2 and d1, d2 d3 in the unstressed chickpea nodules. Lb complexes behave differently during growth phases of the nodules. Lb ‘a’ complex is directly related to the growth and developmental of nodules wherein proportion of Lb a2 content increases with age of nodule accompanying concurrent decrease Lb a1. Early appearance of senescence related isoprotein Lb a2 at vegetative phase of chickpea cultivar correlates its stress-susceptible nature. Further, the turnover rates of Lb a1 to a2 and Lb b were insensitive to reduced supply of photosynthesis during dark stress and even re-illumination. The relative proportion of c2 to c1 inversion increases during darkness. Further, Lb‘d’ complex is affected the most during prolonged darkness. Thus, ratio between individual sub-fractional components of Lbs’ can be correlated with the development phase, longevity and supply of carbohydrates to nodules.

Evidence for a Clathrin-independent mode of endocytosis at a continuously active sensory synapse

Synaptic vesicle exocytosis at chemical synapses is followed by compensatory endocytosis. Multiple pathways including Clathrin-mediated retrieval of single vesicles, bulk retrieval of large cisternae, and kiss-and-run retrieval have been reported to contribute to vesicle recycling. Particularly at the continuously active ribbon synapses of retinal photoreceptor and bipolar cells, compensatory endocytosis plays an essential role to provide ongoing vesicle supply. Yet, little is known about the mechanisms that contribute to endocytosis at these highly complex synapses. To identify possible specializations in ribbon synaptic endocytosis during different states of activity, we exposed mice to controlled lighting conditions and compared the distribution of endocytotic proteins at rod and cone photoreceptor, and ON bipolar cell ribbon synapses with light and electron microscopy. In mouse ON bipolar cell terminals, Clathrin-mediated endocytosis seemed to be the dominant mode of endocytosis at all adaptation states analyzed. In contrast, in mouse photoreceptor terminals in addition to Clathrin-coated pits, clusters of membranously connected electron-dense vesicles appeared during prolonged darkness. These clusters labeled for Dynamin3, Endophilin1, and Synaptojanin1, but not for AP180, Clathrin LC, and hsc70. We hypothesize that rod and cone photoreceptors possess an additional Clathrin-independent mode of vesicle retrieval supporting the continuous synaptic vesicle supply during prolonged high activity.

Questioning photostasis

Photostasis is a phenomenon where the photoreceptor outer segment (OS) length and its rhodopsin content vary depending on environmental lighting. When light is reduced for extended periods, it is argued that OS lengthen and its rhodopsin concentration rises to increase photon capture in darker environment. Increases in OS length may occur because the retinal pigment epithelium (RPE) cells reduce OS consumption in prolonged darkness. But sample sizes in assessing changes in OS length have been small, and results highly varied with no statistical analysis ever offered. Further, animals used were often albinos, which have abnormal RPE cells. Here we keep pigmented and albino mice for 21 days in darkness and compare OS length with those in a normal 12:12 light/dark environment. We measured approximately 1300 OS but found no statistically significant difference in their lengths between light and dark groups in either pigmentation phenotype, although there was a small trend in the data favoring OS extension in the dark. Given that earlier studies were undertaken on limited samples with no statistical analysis, our data pose serious questions for the notion of mammalian photostasis in terms of significant OS plasticity.

Diversity and germination patterns of diatom resting stages at a coastal Mediterranean site

Many planktonic diatoms produce resting stages that survive in the sediment and allow species persistence over periods in which vegetative growth does not occur. With the aim of depicting the annual variability of diatom benthic stage production and understanding the rela- tionships between planktonic and benthic dynamics, we quantified diatoms in surface waters and their viable resting stages in surface sediments at the long-term ecological research station MareChiara (LTER-MC) in the Gulf of Naples (Mediterranean Sea) over 15 mo. A considerable fraction of the diatom species recorded in the water column was also obtained from germination in surface sediments, showing that the formation of resting stages is a widespread life strategy in coastal areas. The most abundant taxa recorded in the plankton were several species of the genera Chaetoceros, Skeletonema, Thalassiosira, Cyclotella, Pseudo-nitzschia and Bacteriastrum. Species of the latter 2 genera were never retrieved from the sediment. Peaks of viable resting stages were generally recorded in the same period as blooms of the individual species in the plankton. Repeated germination experiments with the same sediments demonstrated that some species are more resistant than others to prolonged darkness, while different daylength conditions did not produce a clear effect on germination patterns. This first time-series analysis of a coastal seed bank demonstrates that the assemblage of viable diatoms in the sediment varies over the year, reflecting the diatom dyna mics in the water column, but also species-specific characteristics in survival capability and likely the disturbance due to biotic and abiotic factors.