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The control of seed dormancy by abscisic acid (ABA) has been extensively studied, but the underlying mechanism is not fully understood. Here, we report the characterization of two ABA-related seed dormancy regulators in Arabidopsis (Arabidopsis thaliana): ODR1 (for reversal of rdo5), an ortholog of the rice (Oryza sativa) Seed dormancy4 (Sdr4), and the basic helix-loop-helix transcription factor bHLH57. ODR1, whose transcript levels are directly suppressed by the transcription factor ABA INSENSITIVE3 (ABI3), negatively regulates seed dormancy by affecting ABA biosynthesis and ABA signaling. By contrast, bHLH57 positively regulates seed dormancy by inducing the expression of the genes 9-CIS-EPOXYCAROTENOID DIOXYGENASE6 (NCED6) and NCED9, which encode ABA biosynthetic enzymes, and thus leads to higher ABA levels. ODR1 interacts with bHLH57 and inhibits bHLH57-modulated NCED6 and NCED9 expression in the nucleus. bhlh57 loss-of-function alleles can partially counteract the enhanced NCED6 and NCED9 expression seen in odr1 mutants and can therefore rescue their associated hyper-dormancy phenotype. Thus, we identified a novel ABI3-ODR1-bHLH57-NCED6/9 network that provides insights into the regulation of seed dormancy by ABA biosynthesis and signaling.

The life cycles of plants are characterized by two major life history transitions—germination and the initiation of flowering—the timing of which are important determinants of fitness. Unlike annuals, which make the transition from the vegetative to reproductive phase only once, perennials iterate reproduction in successive years. The floral repressor PERPETUAL FLOWERING 1 (PEP1), an ortholog of FLOWERING LOCUS C, in the alpine perennial Arabis alpina ensures the continuation of vegetative growth after flowering and thereby restricts the duration of the flowering episode. We performed greenhouse and garden experiments to compare flowering phenology, fecundity and seed traits between A. alpina accessions that have a functional PEP1 allele and flower seasonally and pep1 mutants and accessions that carry lesions in PEP1 and flower perpetually. In the garden, perpetual genotypes flower asynchronously and show higher winter mortality than seasonal ones. PEP1 also pleiotropically regulates seed dormancy and longevity in a way that is functionally divergent from FLC. Seeds from perpetual genotypes have shallow dormancy and reduced longevity regardless of whether they after‐ripened in plants grown in the greenhouse or in the experimental garden. These results suggest that perpetual genotypes have higher mortality during winter but compensate by showing higher seedling establishment. Differences in seed traits between seasonal and perpetual genotypes are also coupled with differences in hormone sensitivity and expression of genes involved in hormonal pathways. Our study highlights the existence of pleiotropic regulation of seed traits by hub developmental regulators such as PEP1, suggesting that seed and flowering traits in perennial plants might be optimized in a coordinated fashion., https://doi.org/10.1111/mec.15003

The time of seed germination is a major decision point in the life of plants determining future growth and development. This timing is controlled by seed dormancy, which prevents germination under favourable conditions. The plant hormone abscisic acid (ABA) and the protein DELAY OF GERMINATION 1 (DOG1) are essential regulators of dormancy. The function of ABA in dormancy is rather well understood, but the role of DOG1 is still unknown. Here, we describe four phosphatases that interact with DOG1 in seeds. Two of them belong to clade A of type 2C protein phosphatases: ABA-HYPERSENSITIVE GERMINATION 1 (AHG1) and AHG3. These phosphatases have redundant but essential roles in the release of seed dormancy epistatic to DOG1. We propose that the ABA and DOG1 dormancy pathways converge at clade A of type 2C protein phosphatases., The DOG1 protein is a major regulator of seed dormancy in Arabidopsis. Here, Née et al. provide evidence that DOG1 can interact with the type 2C protein phosphatases AHG1 and AHG3 and that this represents the convergence point of the DOG1-regulated dormancy pathway and signalling by the plant hormone abscisic acid.

A round-robin proficiency test (RR PT) on thin-film multi-junction (MJ) photovoltaic (PV) cells was run between 13 laboratories within the European project CHEETAH. Five encapsulated PV cells were circulated to participants for being tested at Standard Test Conditions (STC). Three cells were a-Si/μc-Si tandem PV devices, each of which had a different short-circuit current ratio between the top junction and the bottom one; the remaining two cells were single-junction PV devices made with material representative of the individual junctions in the MJ cells. The RR PT's main purpose was to assess the capability of the participating laboratories, in terms of employed facilities and procedures, to test MJ PV devices. Therefore, participants were requested to perform STC measurements of all cells according to their own procedure, which might not include external quantum efficiency measurements. The European Solar Test Installation (ESTI) of the Joint Research Centre (JRC) provided the reference calibrations against which the participants' results are compared. ESTI made also a verification of the cells performance at STC at the end of the RR PT, in order to allow a comparison between the initial stable state at which the cells were calibrated (just before circulation) and the one they had reached at the end of the RR PT. The overall results of the RR PT are here presented and discussed together with some aspects of MJ PV testing that emerged as not adequately applied or largely missing. Their full implementation is expected to improve the consistency of future results.

The molecular mechanisms underlying seed dormancy and germination are not fully understood. Here, we show that Arabidopsis thaliana SEED DORMANCY 4-LIKE (AtSdr4L) is a novel specific regulator of dormancy and germination. AtSdr4L encodes a protein with an unknown biochemical function that is localized in the nucleus and is expressed specifically in seeds. Loss of function of AtSdr4L results in increased seed dormancy. The germination of freshly harvested seeds of the Atsdr4l mutant is insensitive to gibberellin (GA). After-ripened mutant seeds are hypersensitive to the GA biosynthesis-inhibitor paclobutrazol but show unaltered sensitivity to abscisic acid. Several GA biosynthesis genes and GA-regulated cell wall remodeling genes are down-regulated in the mutant in both dormant and after-ripened seeds. These results suggest that the Atsdr4l mutation causes both decreased GA biosynthesis and reduced responses. In addition, a genetic analysis indicated that AtSdr4L is epistatic to DELAY OF GERMINATION1 (DOG1) for dormancy and acts upstream of RGA-LIKE 2 (RGL2) in the GA pathway. We propose that AtSdr4L regulates seed dormancy and germination by mediating both the DOG1 and GA pathways.

Histone acetylation is known to affect the speed of seed germination, but the molecular regulatory basis of this remains ambiguous. Here we report that loss of function of two histone deacetylase-binding factors, SWI-INDEPENDENT3 (SIN3)-LIKE1 (SNL1) and SNL2, results in accelerated radicle protrusion and growth during seed germination. AUXIN RESISTANT 1 (AUX1) is identified as a key factor in this process, enhancing germination speed downstream of SNL1 and SNL2. AUX1 expression and histone H3 acetylation at lysines 9 and 18 is regulated by SNL1 and SNL2. The D-type cyclins encoding genes CYCD1;1 and CYCD4;1 display increased expression in AUX1 over-expression lines and the snl1snl2 double mutant. Accordingly, knockout of CYCD4;1 reduces seed germination speed of AUX1 over-expression lines and snl1snl2 suggesting the importance of cell cycling for radicle protrusion during seed germination. Together, our work identifies AUX1 as a link between histone acetylation mediated by SNL1 and SNL2, and radicle growth promoted by CYCD1;1 and CYCD4;1 during seed germination., Histone acetylation influences the speed of seed germination. Here, Wang et al. show that loss of the SNL1/SNL2 histone deacetylase binding factors accelerates seed germination and provide evidence that they act by regulating the expression of AUX1 which in turn influences cell division.

We present PECVD deposition of i-a-Si:H in an in-line configuration for the fabrication of silicon heterojunction solar cells. For industry, in-line processing has the potential to increase production throughput and yield. We compared batch and in-line fabrication of i-a-Si:H passivation samples with identical plasma conditions and observed that the a-Si:H material properties do not significantly differ. In batch-type production the substrate is in the plasma zone at the moment of ignition, whereas for in-line deposition the substrate is introduced into the plasma zone when steady plasma conditions have been reached. Our preliminary results show that there are depositions conditions that result both for in-line and batch-type deposition in good i-a-Si:H passivation layers. Therefore both methods can equally well be considered for the production of silicon heterojunction solar cells. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Before being dispersed in the environment, mature seeds need to be dehydrated. The survival of seeds after dispersal depends on their low hydration in combination with high desiccation tolerance. These characteristics are established during seed maturation. Some key seed maturation genes have been reported to be regulated by alternative splicing (AS). However, so far AS was described only for single genes and a comprehensive analysis of AS during seed maturation has been lacking. We investigated gene expression and AS during Arabidopsis thaliana seed development at a global level, before and after desiccation. Bioinformatics tools were developed to identify differentially spliced regions within genes. Our data suggest the importance and shows the peculiar features of AS during seed desiccation. We identified AS in 34% of genes that are expressed at both timepoints before and after desiccation. Most of these AS transcript variants had not been found before in other tissues. Among the AS genes some seed master regulators could be found. Interestingly, 6% of all expressed transcripts were not transcriptionally regulated during desiccation, but only modified by AS. We propose that AS should be more routinely taken into account in the analysis of transcriptomic data to prevent overlooking potentially important regulators.

Seed dormancy controls the timing of germination, which regulates the adaptation of plants to their environment and influences agricultural production. The time of germination is under strong natural selection and shows variation within species due to local adaptation. The identification of genes underlying dormancy quantitative trait loci is a major scientific challenge, which is relevant for agricultural and ecological goals. In this study, we describe the identification of the DELAY OF GERMINATION18 (DOG18) quantitative trait locus, which was identified as a factor in natural variation for seed dormancy in Arabidopsis (Arabidopsis thaliana). DOG18 encodes a member of the clade A of the type 2C protein phosphatases family, which we previously identified as the REDUCED DORMANCY5 (RDO5) gene. DOG18/RDO5 shows a relatively high frequency of loss-of-function alleles in natural accessions restricted to northwestern Europe. The loss of dormancy in these loss-of-function alleles can be compensated for by genetic factors like DOG1 and DOG6, and by environmental factors such as low temperature. RDO5 does not have detectable phosphatase activity. Analysis of the phosphoproteome in dry and imbibed seeds revealed a general decrease in protein phosphorylation during seed imbibition that is enhanced in the rdo5 mutant. We conclude that RDO5 acts as a pseudophosphatase that inhibits dephosphorylation during seed imbibition.

The control of seed dormancy by ethylene has been well studied, but the underlying molecular mechanisms are not fully understood. Here, we report the characterization of the Arabidopsis (Arabidopsis thaliana) mutant reduced dormancy 3 (rdo3) and the cloning of the underlying gene. We demonstrate that rdo3 is a loss-of-function mutant of the ethylene receptor ETHYLENE RESPONSE1 (ETR1). ETR1 controls seed dormancy partially through the DELAY OF GERMINATION1 (DOG1) pathway. Molecular and genetic analyses demonstrated that ETHYLENE RESPONSE FACTOR12 (ERF12) is involved in the regulation of seed dormancy downstream of ETR1. ERF12 interacts with TOPLESS (TPL) and genetically requires TPL to function. ERF12 and TPL repress the expression of DOG1 by occupying its promoter. Thus, we identified the dormancy pathway ETR1-ERF12-TPL-DOG1 and provide mechanistic insights into the regulation of seed dormancy by linking the ethylene and DOG1 pathways.

Seed quality is affected by different constituents of the seed. In general, seed lots are considered to be of high quality when they exhibit fast and homogeneous germination. When seeds are stored, they undergo different degrees of damage that have detrimental effects on their quality. Therefore, accurate prediction of the seed quality and viability levels of a seed lot is of high importance in the seed-producing industry. Here, we describe the use of activity-based protein profiling of proteases to evaluate the quality of artificially and naturally aged seeds of Arabidopsis thaliana. Using this approach, we have identified two protease activities with opposite behaviours in aged seeds of Arabidopsis that correlate with the quality status of the seeds. We show that vacuolar processing enzymes (VPEs) become more active during the ageing process, in both artificial and natural ageing treatments. Secondly, we demonstrate that serine hydrolases are active at the beginning of our artificial ageing treatment, but their labelling decreases along with seed viability. We present a list of candidate hydrolases active during seed germination and propose that these protease activities can be used in combination with VPEs to develop novel markers of seed quality.

Major sources of efficiency loss in CIGS solar cells are optical losses through reflection and recombination losses at the Mo contact. These losses become increasingly important for thinner cells of 1 micron and less. In our process we are able to reduce those losses by using textured substrates and introduction of a passivation AlOx layer between absorber layer and Mo contact. 2D simulations that we carried out show the potential for high efficiency with thin – textured – partially contacted – electronically passivated devices.

Paper is a cheap substrate which is in principle compatible with the process temperature applied in the plasma enhanced chemical vapour deposition (PECVD) and hot wire CVD (HWCVD) of thin film silicon solar cells. The main drawback of paper for this application is the porosity due to its fibre like structure. The feature size (micrometre scale) is larger than the thickness of the applied photovoltaic layers. To overcome this problem, UV curable lacquer was used to planarize the surface. Plain 80 grams printer paper was taken as a substrate and the lacquer smoothens the rough surface of the paper such that a designed nanostructure can be imprinted for light scattering. In this manner single junction amorphous silicon solar cells with a HWCVD deposited intrinsic layer were processed on paper, without any concessions to the process temperature of 200 °C. The cell performance is comparable to that of reference cells grown on stainless steel, proving that solar cells can be deposited on paper substrates without sacrificing performance. PV on paper could be applied as ”disposable” power source for gadgets, electronic labelling, remote sensing systems, etc. (Internet of Things). (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Dormancy has evolved in plants to restrict germination to favourable growth seasons. Seeds from most crop plants have low dormancy levels due to selection for immediate germination during domestication. Seed dormancy is usually not completely lost and low levels are required to maintain sufficient seed quality.Brassica napuscultivars show low levels of primary seed dormancy. However,B. napusseeds are prone to the induction of secondary dormancy, which can lead to the occurrence of volunteers in the field in subsequent years after cultivation. TheDELAY OF GERMINATION 1(DOG1) gene has been identified as a major dormancy gene in the model plantArabidopsis thaliana.DOG1is a conserved gene and has been shown to be required for seed dormancy in various monocot and dicot plant species. We have identified threeB. napusgenes with high homology toAtDOG1, which we namedBnaA.DOG1.a,BnaC.DOG1.aandBnaC.DOG1.b. The transcripts of these genes could only be detected in seeds and showed a similar expression pattern during seed maturation asAtDOG1. In addition, theBnaDOG1genes showed enhanced transcript levels after the induction of secondary dormancy. These results suggest a role forDOG1in the induction of secondary dormancy inB. napus.

Aims: The aim of this study was to characterize redox changes in the nuclei and cytosol occurring during the mitotic cell cycle in the embryonic roots of germinating Arabidopsis seedlings, and to determine how redox cycling was modified in mutants with a decreased capacity for ascorbate synthesis. Results: Using an in vivo reduction-oxidation (redox) reporter (roGFP2), we show that transient oxidation of the cytosol and the nuclei occurred at G1 in the synchronized dividing cells of the Arabidopsis root apical meristem, with reduction at G2 and mitosis. This redox cycle was absent from low ascorbate mutants in which nuclei were significantly more oxidized than controls. The cell cycle-dependent increase in nuclear size was impaired in the ascorbate-deficient mutants, which had fewer cells per unit area in the root proliferation zone. The transcript profile of the dry seeds and size of the imbibed seeds was strongly influenced by low ascorbate but germination, dormancy release and seed aging characteristics were unaffected. Innovation: These data demonstrate the presence of a redox cycle within the plant cell cycle and that the redox state of the nuclei is an important factor in cell cycle progression. Conclusions: Controlled oxidation is a key feature of the early stages of the plant cell cycle. However, sustained mild oxidation restricts nuclear functions and impairs progression through the cell cycle leading to fewer cells in the root apical meristem. Antioxid. Redox Signal. 27, 1505–1519.

Dormancy is a strategy of higher plants to survive adverse conditions by pausing growth and development, which can occur in different organs like seeds and buds. Dormancy is controlled both by genetic and environmental factors and most of our knowledge about its regulation has been obtained by studying seeds. Seed dormancy is an important adaptive trait in wild plants and has been under negative selection during domestication. The plant hormone abscisic acid has been shown to play a crucial role in the establishment and maintenance of dormancy, whereas gibberellins promote germination. Additional regulators include reactive oxygen species and epigenetic modifications. Large differences in seed dormancy have been found within species and the identification of the underlying genes revealed several novel genes that specifically regulate dormancy. Key Concepts Dormancy allows plants to hold life when conditions do not favour growth. Dormancy is one of the main determinants of timing in the plant life cycle. Dormancy is an adaptive trait with strong variation between and within plant species. Dormancy is regulated both by (epi)genetic and environmental factors. The plant hormone abscisic acid has a crucial role in the establishment and maintenance of dormancy. Specific dormancy regulators show haplotype variation in nature. Keywords: adaptation; after-ripening; DELAY OF GERMINATION 1; domestication; dormancy; dormancy cycling; environment; epigenetic factors; plant hormones

article i nfo The p-type Si layer in a-Si and μc-Si solar cells on foil needs to fulfil several important requirements. The layer is necessary to create the electric field that separates the photo-generated charge carriers; the doping also in- creases the conductivity to conduct the photocurrent to the front contact; on the other hand, the p-layer should transmit the incident light efficiently to the intrinsic absorber layer. We show that it is possible to study TEM samples prepared, for analysis of possible layer defects, by focussed ion beam milling to detect boron and carbon concentrations as low as 10 20 cm -3 , using core-loss EELS combined with numerical analysis. Wecontrol the band gap and activation energyofp-a-SiC by varyingthe B2H6and CH4 flowduring depositionintheprocesschamber. We have found a linear relation between the activation energy of the dark conductivity Eact and the optical band gap E04. Modelling shows that the optimum efficiency in nip solar cells is obtained when the p-a-SiC band gap is slightly larger than the band gap of the absorber layer. We have assessed the potential of core-loss EELS for detecting B and C concentrations as low as 10 20 cm -3 in a spatially resolved manner, and of low-loss EELS as a probe of the local variations in plasmon energy.

Seed dormancy is an important component of plant fitness that causes a delay of germination until the arrival of a favourable growth season. Dormancy is a complex trait that is determined by genetic factors with a substantial environmental influence. Several of the tissues comprising a seed contribute to its final dormancy level. The roles of the plant hormones abscisic acid and gibberellin in the regulation of dormancy and germination have long been recognized. The last decade saw the identification of several additional factors that influence dormancy including dormancy-specific genes, chromatin factors and non-enzymatic processes. This review gives an overview of our present understanding of the mechanisms that control seed dormancy at the molecular level, with an emphasis on new insights. The various regulators that are involved in the induction and release of dormancy, the influence of environmental factors and the conservation of seed dormancy mechanisms between plant species are discussed. Finally, expected future directions in seed dormancy research are considered.

Nuclei in dry Arabidopsis thaliana seeds are very small and have highly condensed chromatin. Nuclear shrinkage and chromatin compaction occur during seed maturation and have been shown to be independent, developmentally controlled processes. To confirm this genetically, we studied chromatin compaction in a mutant of the seed developmental regulator ABA INSENSITIVE 3, and in a double mutant of the nuclear matrix proteins LITTLE NUCLEI 1 and 2. Our results indicated that the nuclear shrinking and chromatin condensation during seed maturation can be genetically uncoupled, confirming that these are independent processes. In addition, we demonstrated that transcript levels of siliques toward the end of seed maturation are comparable to those in vegetative tissues, despite the highly compacted chromatin, small nuclear volume and low hydration status of seeds.

The standard way to improve the light management of thin film solar cells is to introduce a light scattering structure, either on the front window or at the back reflector. Usually, growth conditions of TCO layers are adjusted to get random surface roughness on the front window. In this paper we present an alternative method, which can be applied both on the front window and at the back reflector. It involves imprinting a UV curable coating layer allowing full control on the texture (random or periodic) to fully optimise the light trapping. Light trapping is even more important for microcrystalline Si solar cells. We have fabricated thin film nip Si solar cells with sputtered Ag/ZnO back contacts on embossed barrier layers on steel foil. We show that the UV curable coating is well-suited as imprintable barrier layer between the steel foil and the active layers. For nip a-Si cells we can obtain light trapping, as measured by the short-circuit current, that is almost as good as that of nip a-Si cells made on Asahi U-type glass, covered with a Ag/ZnO back reflector. Furthermore, we show that dynamically processed a-Si nip cells on foil realised efficiencies of over 7%, which are only slightly less than for cells made in a UHV lab-scale cluster tool in static processing. Finally, a-Si/a-Si tandems and μc-Si/a-Si tandems have been fabricated. Initial efficiencies of around 8% on textured barrier layer on steel foil have been achieved.

Most plant species rely on seeds for their dispersal and survival under unfavorable environmental conditions. Seeds are characterized by their low moisture content and significantly reduced metabolic activities. During the maturation phase, seeds accumulate storage reserves and become desiccation-tolerant and dormant. Growth is resumed after release of dormancy and the occurrence of favorable environmental conditions. Here we show that embryonic cotyledon nuclei of Arabidopsis thaliana seeds have a significantly reduced nuclear size, which is established at the beginning of seed maturation. In addition, the chromatin of embryonic cotyledon nuclei from mature seeds is highly condensed. Nuclei regain their size and chromatin condensation level during germination. The reduction in nuclear size is controlled by the seed maturation regulator ABSCISIC ACID-INSENSITIVE 3, and the increase during germination requires two predicted nuclear matrix proteins, LITTLE NUCLEI 1 and LITTLE NUCLEI 2. Our results suggest that the specific properties of nuclei in ripe seeds are an adaptation to desiccation, independent of dormancy. We conclude that the changes in nuclear size and chromatin condensation in seeds are independent, developmentally controlled processes.

At the front contact of thin film silicon solar cells, the junction between the p-doped window layer and the n-type transparent electrode results in a barrier that must be surmounted by the charge carriers. The barrier height is governed by the work function difference of these two materials. For different compositions of the well known In2O3-SnO2 (ITO) system, we find that higher oxygen partial pressure during sputter deposition increases the work function of the deposited films. Over the same range of oxygen partial pressures, ITO electrodes with low tin content applied to n-i-p type thin film silicon solar yield a gain in Voc by up to 40 mV. *

Seasonal germination timing of Arabidopsis thaliana strongly influences overall life history expression and is the target of intense natural selection. This seasonal germination timing depends strongly on the interaction between genetics and seasonal environments both before and after seed dispersal. DELAY OF GERMINATION 1 (DOG1) is the first gene that has been identified to be associated with natural variation in primary dormancy in A. thaliana. Here, we report interaccession variation in DOG1 expression and document that DOG1 expression is associated with seed-maturation temperature effects on germination; DOG1 expression increased when seeds were matured at low temperature, and this increased expression was associated with increased dormancy of those seeds. Variation in DOG1 expression suggests a geographical structure such that southern accessions, which are more dormant, tend to initiate DOG1 expression earlier during seed maturation and achieved higher expression levels at the end of silique development than did northern accessions. Although elimination of the synthesis of phytohormone abscisic acid (ABA) results in the elimination of maternal temperature effects on dormancy, DOG1 expression predicted dormancy better than expression of genes involved in ABA metabolism.

ECN is developing n-i-p solar cells based on a-Si and μc-Si absorber layers deposited with inline PECVD, using linear plasma sources, on an imprint-textured UV curable coating layer on foil. We show that solar cells deposited on foil with random texture can achieve good light trapping (Jsc ∼ 15-16mA/cm2 for a-Si cells). Furthermore, we show that a-Si nip cells on foil, processed in dynamic mode in an industrial pilot roll-to-roll system for 30cm wide foils, can achieve efficiencies (of over 7%). Future work will focus on developing and implementing optimised periodic nanotextures for μc-Si and micromorph tandem.

The Kelvin probe is a non-contact, non-destructive vibrating capacitor device that measures the work function difference between a conducting sample and a vibrating tip. This contribution focuses on inline monitoring of the surface (photo)voltage of deposited silicon layers. We apply a custom-built in situ Kelvin probe, operated in a roll-to-roll PECVD system, located immediately after the plasma zones to enable direct feedback to the controlling system of the plasma deposition. The surface photovoltage of nip thin film Si solar cells increases with increasing V oc . The results imply that inline, contactless measurements of the open-circuit voltage are possible and that thus monitoring the doped layer quality during roll-to-roll production is feasible.

• Seed longevity is an important trait in many crops and is essential for the success of most land plant species. Current knowledge of its molecular regulation is limited. The Arabidopsis mutants abscisic acid insensitive3-5 (abi3-5) and leafy cotyledon1-3 (lec1-3) have impaired seed maturation and quickly lose seed viability. abi3-5 and lec1-3 were used as sensitized genetic backgrounds for the study of seed longevity. • We exploited the natural variation of Arabidopsis to create introgression lines from the Seis am Schlern and Shahdara accessions in, respectively, the abi3-5 and lec1-3 backgrounds. These lines carry natural modifiers of the abi3 and lec1 phenotypes. Longevity tests and a proteomic analysis were conducted to describe the seed physiology of each line. • The modifier lines showed improved seed longevity. The Shahdara modifiers can partially re-establish the seed developmental programs controlled by LEC1 and restore the accumulation of seed storage proteins that are reduced in abi3-5 and lec1-3. • The isolation and characterization of natural modifiers of the seed maturation mutants abi3-5 and lec1-3, and the analysis of their seed proteomes, advance our current understanding of seed longevity

A roll-to-roll PECVD system for thin film silicon solar cells on steel foil has been developed by ECN in collaboration with Roth and Rau AG. It combines MW-PECVD for fast deposition of intrinsic Si and novel linear RF sources, which apply very mild deposition conditions, for the growth of doped Si layers. The RF and MW sources can be easily scaled up to deposition widths of up to 150 cm. Here, we report on n-type doping, achieved by RF-PECVD from a H 2 /SiH 4 /PH 3 mixture in the reaction chamber. The best n-type a-Si:H layers showed E act = 0.27 eV and σ d = 2.7 x 10 -3 S/cm. Also thin layers down to 20 nm were of device quality and were deposited at a rate of 0.4 A/s. Furthermore, n-type μc-Si:H layers with thicknesses of 150 nm, with E act = 0.034 eV and σ d = 2 S/cm were grown. Good quality n-type pc-Si:H layers can be made for layer thicknesses down to 50 nm at a rate of 0.15 A/s. To conclude, the novel RF source is well-suited for the growth of n-doped a-Si:H and μc-Si:H layers for roll-to-roll solar cell production.

The transcriptional regulator CONSTANS (CO) promotes flowering of Arabidopsis under long summer days (LDs) but not under short winter days (SDs). Post-translational regulation of CO is crucial for this response by stabilizing the protein at the end of a LD, whereas promoting its degradation throughout the night under LD and SD. We show that mutations in CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a component of a ubiquitin ligase, cause extreme early flowering under SDs, and that this is largely dependent on CO activity. Furthermore, transcription of the CO target gene FT is increased in cop1 mutants and decreased in plants overexpressing COP1 in phloem companion cells. COP1 and CO interact in vivo and in vitro through the C-terminal region of CO. COP1 promotes CO degradation mainly in the dark, so that in cop1 mutants CO protein but not CO mRNA abundance is dramatically increased during the night. However, in the morning CO degradation occurs independently of COP1 by a phytochrome B-dependent mechanism. Thus, COP1 contributes to day length perception by reducing the abundance of CO during the night and thereby delaying flowering under SDs.

Microwave plasma-enhanced chemical vapor deposition (PECVD) is a very promising method for industrial scale fabrication of microcrystalline silicon solar cells since the technique is well applicable for large areas, and high deposition rates can be obtained. We have investigated the effect of Ar dilution on the growth process and the material properties of microcrystalline silicon. The major benefit of Ar addition in the MWPECVD process, using H 2 and SiH 4 as reactant gases, is an improved stabilization of the plasma, in particular at low pressure and MW power. We show, however, that material properties of the microcrystalline silicon layers deteriorate if we partly substitute H 2 by Ar during the deposition. The density of the layers – as expressed by the refractive index – decreases, and the defect density (measured by Fourier transform photocurrent spectroscopy) increases with increasing Ar flow. Investigation of the plasma by optical emission study shows that Ar atoms play a very active role in the dissociation processes of H 2 and SiH 4 . Substitution of H 2 by Ar decreases the SiH ⁎ emission and increases the Si ⁎ emission. On the other hand, the H α /H β ratio increases upon substitution of H 2 by Ar. The latter effect shows that Ar addition does not lead to higher electron temperatures and we conclude that the changes of SiH ⁎ and Si ⁎ emissions are due to dissociation of SiH 4 by Ar ⁎ (quenching reactions). The precise role of Ar in MWPECVD of microcrystalline silicon needs further investigation, but we conclude that the usage of this gas should be minimized in order to maximize the quality of the silicon layers.

Seed dormancy is defined as the failure of a viable seed to germinate under favorable conditions. Besides playing an adaptive role in nature by optimizing germination to the most suitable time, a tight control of dormancy is important in crop plants. Extensive genetic and physiological studies have identified the involvement of several factors, but the molecular mechanisms underlying this process are still largely unknown. We cloned the HISTONE MONOUBIQUITINATION1 (HUB1) gene, of which the mutant (previously identified as reduced dormancy4) has reduced seed dormancy and several pleiotropic phenotypes. HUB1 encodes a C3HC4 RING finger protein. The Arabidopsis thaliana genome contains one HUB1 homolog, which we named HUB2. The hub2 mutant also has reduced seed dormancy and is not redundant with hub1. Homologs of HUB1 and HUB2 in other species are required for histone H2B monoubiquitination. In agreement with this, the ubiquitinated form of histone H2B could not be detected in the hub1 and hub2 mutants. In yeast and human cells, histone H2B monoubiquitination is associated with actively transcribed genes. The hub1 mutant showed altered expression levels for several dormancy-related genes. We propose a role for chromatin remodeling in seed dormancy by H2B monoubiquitination through HUB1 and HUB2.

The Arabidopsis protein DELAY OF GERMINATION 1 (DOG1) is a key regulator of seed dormancy, which is a life history trait that determines the timing of seedling emergence. The amount of DOG1 protein in freshly harvested seeds determines their dormancy level. DOG1 has been identified as a major dormancy QTL and variation in DOG1 transcript levels between accessions contributes to natural variation for seed dormancy. The DOG1 gene is alternatively spliced. Alternative splicing increases the transcriptome and proteome diversity in higher eukaryotes by producing transcripts that encode for proteins with altered or lost function. It can also generate tissue specific transcripts or affect mRNA stability. Here we suggest a different role for alternative splicing of the DOG1 gene. DOG1 produces five transcript variants encoding three protein isoforms. Transgenic dog1 mutant seeds expressing single DOG1 transcript variants from the endogenous DOG1 promoter did not complement because they were non-dormant and lacked DOG1 protein. However, transgenic plants overexpressing single DOG1 variants from the 35S promoter could accumulate protein and showed complementation. Simultaneous expression of two or more DOG1 transcript variants from the endogenous DOG1 promoter also led to increased dormancy levels and accumulation of DOG1 protein. This suggests that single isoforms are functional, but require the presence of additional isoforms to prevent protein degradation. Subsequently, we found that the DOG1 protein can bind to itself and that this binding is required for DOG1 function but not for protein accumulation. Natural variation for DOG1 binding efficiency was observed among Arabidopsis accessions and contributes to variation in seed dormancy., Author Summary The Arabidopsis protein DELAY OF GERMINATION 1 (DOG1) is an important regulator of seed dormancy and controls the timing of seedling emergence. The amount of DOG1 protein in mature seeds correlates with their dormancy level. It has been demonstrated that DOG1 is an important contributor to natural variation for seed dormancy and Arabidopsis accessions vary in their DOG1 levels. In this study we showed that the DOG1 gene produces five transcript variants encoding three protein isoforms. Transgenic dog1 mutant seeds expressing single DOG1 transcript variants lack dormancy and do not accumulate DOG1 protein. Simultaneous expression of two or more DOG1 transcript variants encoding different isoforms, however, leads to the accumulation of DOG1 protein and increased seed dormancy. DOG1 protein can bind to itself and Arabidopsis seeds that contain a DOG1 variant unable to bind show reduced seed dormancy. We observed variation for DOG1 binding efficiency between Arabidopsis accessions, indicating a role for DOG1 self-binding in natural variation for seed dormancy.

A unique feature of late-flowering fwa epigenetic mutations is that the phenotype is caused by ectopic expression of the homeobox gene FWA. During normal development the FWA gene is expressed specifically in the endosperm in an imprinted manner. Ectopic FWA expression and disruption of imprinting can be induced in mutants of a CG methyltransferase MET1 (methyltransferase 1) or a chromatin-remodeling gene DDM1 (decrease in DNA methylation 1), suggesting that the proper FWA expression depends on cytosine methylation. However, critical methylated residues controlling FWA silencing are not pinpointed. Nor is it understood how the FWA gene is initially methylated and silenced in wild-type plants. Here we mapped sequences critical for FWA silencing by application of RdDM (RNA-directed DNA methylation) to a ddm1-induced stable fwa epiallele. Transcription of double-stranded RNA corresponding to the tandem direct repeats around the FWA transcription start site induced de novo DNA methylation, transcriptional suppression and phenotypic reversion. The induced changes were heritable even without the transgene, which correlates with inheritance of CG methylation in the direct repeats. The newly silenced FWA allele was transcribed in an endosperm-specific and imprinted manner, as is the case for the wild-type FWA gene. The results indicate that methylation of the direct repeats, which presumably originated from a short interspersed nuclear element (SINE), is sufficient to induce proper epigenetic control of the FWA gene.

A new regime of high rate deposition of near-stoichiometric silicon nitride by Hot Wire Chemical Vapor Deposition was investigated. The layers were tested on multicrystalline silicon solar cells in order to assess their antireflection and passivation properties. The present design of the filament arrangement and the showerhead gas supply system allows for virtually unlimited scale-up and deposition rates of around 3 nm/s were obtained. By varying the SiH 4 flow, the refractive index at 630 nm (n) could be controlled from 1.90±0.05 to 2.12±0.05, and the extinction coefficient at 400 nm (k) was

Bulk and surface passivation by silicon nitride has become an indispensable element in industrial production of multicrystalline silicon (mc-Si) solar cells. Microwave PECVD is a very effective method for high-throughput deposition of silicon nitride layers with the required properties for bulk and surface passivation. In this paper an analysis is presented of the relation between deposition parameters of microwave PECVD and material properties of silicon nitride. By tuning the process conditions (substrate temperature, gas flows, working pressure) we have been able to fabricate silicon nitride layers which fulfill almost ideally the four major requirements for mc-Si solar cells: (1) good anti-reflection coating (refractive index tunable between 2·0 and 2·3); (2) good surface passivation on p-type FZ wafers (Seff

The influence of a short high-temperature step, comparable to the so-called "firing" of the metallization on silicon solar cells, on properties of high-rate (>0.5 nm/s) plasma deposited silicon nitride (a-SiNx:H) films has been investigated. These a-SiNx:H films are used as antireflection coating on multicrystalline silicon (mc-Si) solar cells and, after the firing process, they also induce hydrogen bulk passivation in the mc-Si. Three different types of remote plasma deposited a-SiNx:H films have been investigated: (i) expanding thermal plasma (ETP) deposited a-SiNx:H films from a N2–SiH4 gas mixture, (ii) ETP deposited a-SiNx:H films from a NH3–SiH4 mixture, and (iii) microwave plasma deposited a-SiNx:H films from a NH3–SiH4 mixture. The atomic composition and optical and structural properties of the films have been studied before and after the high-temperature step by the combination of elastic recoil detection, spectroscopic ellipsometry, and Fourier transform infrared spectroscopy. It has been observed that the high-temperature step can induce significant changes in hydrogen content, bonding types, mass density, and optical absorption of the films. These thermally induced effects are more enhanced for Si- than for N-rich films, which in some cases have a high thermal stability. Furthermore, the material properties and the influence of the high-temperature step have been related to the bulk passivation properties of the a-SiNx:H coated mc-Si solar cells. It is found that in particular the density and thermal stability of the a-SiNx:H films seem to be important for the degree of the bulk passivation obtained.

Silicon nitride (a-SiNx:H) films deposited by the expanding thermal plasma at high rate (> 1 nm/s) have been studied for application as anti-reflection coatings for multicrystalline silicon (mc-Si) solar cells. Internal quantum efficiency measurements have revealed that bulk passivation is achieved after a firing-through process of the a-SiNx:H as deposited from NH3/SiH4 and N2/SiH4 plasmas. However, the a-SiNx:H films deposited from N2/SiH4 show a lower passivation quality than those deposited from NH3/SiH4. This has been attributed to a poorer thermal stability of the films deposited from the N2/SiH4 plasma, resulting in structural changes within the film during the firing step. Copyright © 2002 John Wiley & Sons, Ltd.

Optical simulations of 4-terminal hybrid tandem modulescombining high-efficiency crystalline silicon(c-Si) cells with three different thin-film top cells respectively are presented. We considered three types of thin film PV cells: 1. Enlarged-bandgap oxygenated amorphous silicon (a-SiO:H) cells, 2. Wide-bandgap chalcopyrite (CuGaSe2) cells, and 3. Perovskite (CH3NH3PbI3) cells. A methodology for evaluating the efficiency gain of the 4-terminal hybrid tandem module is proposed and used to show how the efficiency of aninterdigitated back contact (IBC)c-Si module with an efficiency of about 19.5% can significantly be increased through this 4-terminal tandem concept. In our model we also included the change in electrical output parameters by the color-filtering effect of the top cells.

We propose a model for heterochromatin assembly that links DNA methylation with histone methylation and DNA replication. The hypomethylated Arabidopsis mutants ddm1 and met1 were used to investigate the relationship between DNA methylation and chromatin organization. Both mutants show a reduction of heterochromatin due to dispersion of pericentromeric low‐copy sequences away from heterochromatic chromocenters. DDM1 and MET1 control heterochromatin assembly at chromocenters by their influence on DNA maintenance (CpG) methylation and subsequent methylation of histone H3 lysine 9. In addition, DDM1 is required for deacetylation of histone H4 lysine 16. Analysis of F 1 hybrids between wild‐type and hypomethylated mutants revealed that DNA methylation is epigenetically inherited and represents the genomic imprint that is required to maintain pericentromeric heterochromatin.

The transition to flowering is a crucial moment in a plant’s life cycle of which the mechanism has only been partly revealed. In a screen for early flowering, after mutagenesis of the late-flowering fwa mutant of Arabidopsis thaliana, the early flowering in short days (efs) mutant was identified. Under long-day light conditions, the recessive monogenic efs mutant flowers at the same time as wild type but, under short-day conditions, the mutant flowers much earlier. In addition to its early-flowering phenotype, efs has several pleiotropic effects such as a reduction in plant size, fertility and apical dominance. Double mutant analysis with several late-flowering mutants from the autonomous promotion (fca and fve) and the photoperiod promotion (co, fwa and gi) pathways of flowering showed that efs reduces the flowering time of all these mutants. However, efs is completely epistatic to fca and fve but additive to co, fwa and gi, indicating that EFS is an inhibitor of flowering specifically involved in the autonomous promotion pathway. A vernalisation treatment does not further reduce the flowering time of the efs mutant, suggesting that vernalisation promotes flowering through EFS. By comparing the length of the juvenile and adult phases of vegetative growth for wild-type, efs and the double mutant plants, it is apparent that efs mainly reduces the length of the adult phase.

▪ Abstract The timing of the transition from vegetative to reproductive development is of great fundamental and applied interest but is still poorly understood. Recently, molecular-genetic approaches have been used to dissect this process in Arabidopsis. The genetic variation present among a large number of mutants with an early- or late-flowering phenotype, affecting the control of both environmental and endogenous factors that influence the transition to flowering, is described. The genetic, molecular, and physiological analyses have led to identification of different components involved, such as elements of photoperception and the circadian rhythm. Furthermore, elements involved in the signal transduction pathways to flowering have been identified by the cloning of some floral induction genes and their target genes.

In the European project Silicon-Light we developed concepts and technologies to increase conversion efficiencies of thin film silicon solar cells on foil. Main focus was put on improved light management, using NIL for creating light scattering textures, improved TCOs using sputtering, and improved silicon absorber material made by PECVD. On foil we achieved initial cell efficiencies of 11% and on rigid substrates stable efficiencies of 11.6% were achieved. Finally, the project demonstrated the industrial scale feasibility of the developed technologies and materials. Cost of ownership calculations showed that implementation of these technologies on large scale would enable the production of these high efficiency solar modules at manufacturing cost of 0.65 €/Wp with encapsulation costs (0.20 €/Wp) being the dominant costs. Life cycle analysis showed that large scale production of modules based on the technologies developed in Silicon-Light would have an energy payback time of 0.85 years in Central European countries.

Histone (de)acetylation is a highly conserved chromatin modification that is vital for development and growth. In this study, we identified a role in seed dormancy for two members of the histone deacetylation complex in Arabidopsis thaliana, SIN3-LIKE1 (SNL1) and SNL2. The double mutant snl1 snl2 shows reduced dormancy and hypersensitivity to the histone deacetylase inhibitors trichostatin A and diallyl disulfide compared with the wild type. SNL1 interacts with HISTONE DEACETYLASE19 in vitro and in planta, and loss-of-function mutants of SNL1 and SNL2 show increased acetylation levels of histone 3 lysine 9/18 (H3K9/18) and H3K14. Moreover, SNL1 and SNL2 regulate key genes involved in the ethylene and abscisic acid (ABA) pathways by decreasing their histone acetylation levels. Taken together, we showed that SNL1 and SNL2 regulate seed dormancy by mediating the ABA-ethylene antagonism in Arabidopsis. SNL1 and SNL2 could represent a cross-link point of the ABA and ethylene pathways in the regulation of seed dormancy.

Seeds are essential for reproduction and dispersal of most plant species and constitute a major human food source. The life of a seed is characterised by two major phase transitions, from embryogenesis to seed maturation and from dry seed to germination. These different stages are characterised by specific transcriptomes and require silencing and activation of diverse sets of genes. In addition, fully mature seeds contain very small nuclei with highly compacted chromatin, which is established during seed maturation. These unique characteristics require extensive epigenetic signalling mechanisms to tightly coordinate the phase transitions and control chromatin accessibility. This chapter gives an overview of our present knowledge of the role of epigenetics in the life of seeds, focussing on the later stages of seed development, dormancy and germination in Arabidopsis thaliana.

Electron energy-loss spectroscopy (EELS) is used to study p-doped layers in n-i-p amorphous thin film Si solar cells grown on steel foil substrates. For a solar cell in which an intrinsic amorphous hydrogenated Si (a-Si-H) layer is sandwiched between 10-nm-thick n-doped and p-doped a-Si:H layers, we assess whether core-loss EELS can be used to quantify the B concentration. We compare the shape of the measured B K edge with real space ab initio multiple scattering calculations and show that it is possible to separate the weak B K edge peak from the much stronger Si L edge fine structure by using log-normal fitting functions. The measured B concentration is compared with values obtained from secondary ion mass spectrometry, as well as with EELS results obtained from test samples that contain ∼200-nm-thick a-Si:H layers co-doped with B and C. We also assess whether changes in volume plasmon energy can be related to the B concentration and/or to the density of the material and whether variations of the volume plasmon line-width can be correlated with differences in the scattering of valence electrons in differently doped a-Si:H layers. Fil: Duchamp, M.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; Alemania Fil: Boothroyd, C.B.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; Alemania Fil: Moreno, Mario Sergio Jesus. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina Fil: Van Aken, B.B.. No especifíca; Fil: Soppe, W.J.. No especifíca; Fil: Dunin-Borkowski, R.E.. Helmholtz Gemeinschaft. Forschungszentrum Jülich; Alemania