AbstractOur solar system's path has recently been shown to potentially intersect dense interstellar clouds 2 and 7 million years ago: the Local Lynx of Cold Cloud and the edge of the Local Bubble. These clouds compressed the heliosphere, directly exposing Earth to the interstellar medium. Previous studies that examined climate effects of these encounters argued for an induced ice age due to the formation of global noctilucent clouds (NLCs). Here, we revisit such studies with a modern 2D atmospheric chemistry model using parameters of global heliospheric magnetohydrodynamic models as input. We show that NLCs remain confined to polar latitudes and short seasonal lifetimes during these dense cloud crossings lasting ∼105 years. Polar mesospheric ozone becomes significantly depleted, but the total ozone column broadly increases. Furthermore, we show that the densest NLCs lessen the amount of sunlight reaching the surface instantaneously by up to 7% while halving outgoing longwave radiation.

The establishment of plant architecture requires coordination of distinct processes including shoot branching and apical dominance (AD). AD involves the bud apical shoot, mainly through indole-3-acetic acid (IAA) synthetized by the cells of the meristem and young leaves. The rootward flow generates an auxin gradient in the stem and buds, regulating lateral bud (LB) outgrowth. Phytochromes and AD are involved in the shade-avoidance syndrome in woody plants. However, the underlying mechanisms remain poorly understood. The aim of this study was to evaluate the sensitivity of cherry rootstocks to light, mediated by the photoreceptor phytochrome, and its effect on the role of auxin in driving branching by AD. Pharmacological treatments using transport inhibitors and a competitor of IAA were applied to transgenic lines of Colt cherry rootstock, which showed different sensitivities to light because of the ectopic expression of a rice phyA gene. Results showed different physiological behaviours among the transgenic lines and between themselves and the Colt-wt line. Exogenous IBA inhibited Colt-wt LB outgrowth, and this inhibition was less intense in transgenic lines. The IAA-inhibitors and IAA-competitor promoted branching. In in vitro phyA-transgenic plantlets, the ectopic gene induced greater branching and a higher number of buds developed in new shoots. This work confirms a positive action of phytochrome on lateral branching in cherry rootstock, playing a role in the regulation of AD. Moreover, we suggest that the confined in vitro system might now be used as a phenotyping screening to test the plasticity of the response, highlighting the behaviour of modified genotypes due to an ectopic insertion event by simple and rapid procedures.

The spectacular outbursts of energy associated with supernovae (SNe) have long motivated research into their potentially hazardous effects on Earth and analogous environments. Much of this research has focused primarily on the atmospheric damage associated with the prompt arrival of ionizing photons within days or months of the initial outburst, and the high-energy cosmic rays that arrive thousands of years after the explosion. In this study, we turn the focus to persistent X-ray emission, arising in certain SNe that have interactions with a dense circumstellar medium and observed months and/or years after the initial outburst. The sustained high X-ray luminosity leads to large doses of ionizing radiation out to formidable distances. We assess the threat posed by these X-ray-luminous SNe for Earth-like planetary atmospheres; our results are rooted in the X-ray SN observations from Chandra, Swift-XRT, XMM-Newton, NuSTAR, and others. We find that this threat is particularly acute for SNe showing evidence of strong circumstellar interaction, such as Type IIn explosions, which have significantly larger ranges of influence than previously expected and lethal consequences up to ∼50 pc away. Furthermore, X-ray-bright SNe could pose a substantial and distinct threat to terrestrial biospheres and tighten the Galactic habitable zone. We urge follow-up X-ray observations of interacting SNe for months and years after the explosion to shed light on the physical nature and full-time evolution of the emission and to clarify the danger that these events pose for life in our galaxy and other star-forming regions.

We have reevaluated recent studies of the effects on Earth by cosmic rays (CRs) from nearby supernovae (SNe) at 100 and 50 pc, in the diffusive transport CR case, here including an early-time suppression at lower CR energies neglected in the previous works. Inclusion of this suppression leads to lower overall CR fluxes at early times, lower atmospheric ionization, smaller resulting ozone depletion, and lower sea-level muon radiation doses. Differences in the atmospheric impacts are most pronounced for the 100 pc case with less significant differences in the 50 pc case. We find a greater discrepancy in the modeled sea-level muon radiation dose, with significantly smaller dose values in the 50 pc case; our results indicate it is unlikely that muon radiation is a significant threat to the biosphere for SNe beyond 20 pc, for the diffusive transport case. We have also performed new modeling of the effects of SN CRs at 20 and 10 pc. Overall, our results indicate that, considering only the effects of CRs, the "lethal" SN distance should be closer to 20 pc rather than the typically quoted 8-10 pc. Recent work on extended SN X-ray emission indicates significant effects out to 50 pc and therefore the case is now strong for increasing the standard SN lethal distance to at least 20 pc. This has implications for studies of the history of life on Earth as well as considerations of habitability in the Galaxy.

Recent studies of the effects on the Earth's atmosphere by astrophysical sources, such as nearby gamma-ray bursts or supernovae, have shown that these events could lead to severe changes in atmospheric composition. Depletion of ozone, the most notable of these changes, is extremely dangerous to living organisms as any decrease in ozone levels leads to an increase in the irradiance of harmful solar radiation at the Earth's surface. In this work we consider dark matter as an astrophysical source of gamma rays, by the annihilation and decay of WIMPs found within dark compact halo objects known as UltraCompact Minihaloes (UCMHs). We calculate the fluence of gamma rays produced in this way and simulate the resulting changes to terrestrial ozone levels using the Goddard Space Flight Center 2D Atmospheric Model. We also calculate the rate at which such events would occur, using estimates for the mass distribution of these haloes within the Milky Way. We find that the ozone depletion from UCMHs can be significant, and even of similar magnitude to the levels which have been linked to the cause of the Late-Ordovician mass extinction event. However, the probability of such encounters over the Earth's entire history is relatively low. This suggests that, while dark compact objects like UCMHs could have had an impact on the Earth's biosphere, other astrophysical phenomena like gamma-ray bursts or supernovae seem a more likely source of these effects.

Pathogenesis-related (PR) proteins are part of the systemic signaling network that perceives pathogens and activates defenses in the plant. Eukaryotic and bacterial species have a 24-h ‘body clock’ known as the circadian rhythm. This rhythm regulates an organism’s life, modulating the activity of the phytochromes (phys) and cryptochromes (crys) and the accumulation of the corresponding mRNAs, which results in the synchronization of the internal clock and works as zeitgeber molecules. Salicylic acid accumulation is also under light control and upregulates the PR genes expression, increasing plants’ resistance to pathogens. Erwinia amylovora causes fire blight disease in pear trees. In this work, four bacterial transcripts (erw1-4), expressed in asymptomatic E. amylovora-infected pear plantlets, were isolated. The research aimed to understand how the circadian clock, light quality, and related photoreceptors regulate PR and erw genes expression using transgenic pear lines overexpressing PHYB and CRY1 as a model system. Plantlets were exposed to different circadian conditions, and continuous monochromic radiations (Blue, Red, and Far-Red) were provided by light-emitting diodes (LED). Results showed a circadian oscillation of PR10 gene expression, while PR1 was expressed without clear evidence of circadian regulation. Bacterial growth was regulated by monochromatic light: the growth of bacteria exposed to Far-Red did not differ from that detected in darkness; instead, it was mildly stimulated under Red, while it was significantly inhibited under Blue. In this regulatory framework, the active form of phytochrome enhances the expression of PR1 five to 15 fold. An ultradian rhythm was observed fitting the zeitgeber role played by CRY1. These results also highlight a regulating role of photoreceptors on the expression of PRs genes in non-infected and infected plantlets, which influenced the expression of erw genes. Data are discussed concerning the regulatory role of photoreceptors during photoperiod and pathogen attacks.

Onion bulb initiation is photoperiod-dependent. Understanding this is crucial for adapting new varieties for growth at different latitudes, as well as aiding germplasm screening for the choice of current varieties. This study aims to gain further understanding of the molecular mechanisms involved in onion bulbing process based on the parallels with well-characterised functional clock genes in the Arabidopsis flowering pathway. A comprehensive set of diurnal quantitative expression experiments was carried out to investigate the bulbing response in two different onion varieties, namely Renate, a long-day variety and Hojem, a short-day variety under increasing intermediate day-lengths. All onion homologous to Arabidopsis flowering time genes showed clear diurnal expression patterns peaking at different times of the day for both long/short-day onions, indicating their role in daylength dependent bulbing process at molecular level. Under intermediate daylengths, AcFT1 expression level increased with daylengths in both varieties, while AcFT4 was expressed in all daylengths. The two genes showed complementary expression with AcFT4 peaking in the morning and AcFT1 in the evening in longer days. The results indicate that AcFT1 and AcFT4 are negatively co-regulated, but AcFT1 is the predominant regulator of bulb formation in response to daylength.

We analyse the additional effect on planetary atmospheres of recently detected gamma-ray burst afterglow photons in the range up to 1 TeV. For an Earth-like atmosphere, we find that there is a small additional depletion in ozone versus that modeled for only prompt emission. We also find a small enhancement of muon flux at the planet surface. Overall, we conclude that the additional afterglow emission, even with TeV photons, does not result in a significantly larger impact over that found in past studies.

As part of the collaboration between the Trustees and Publishers of the Journal of Horticultural Science and Biotechnology, an annual monetary prize was established for the paper with the most impa...

Motivated by the occurrence of a moderately nearby supernova near the beginning of the Pleistocene, possibly as part of a long-term series beginning in the Miocene, we investigated whether nitrate rainout resulting from the atmospheric ionization of enhanced cosmic ray flux could have, through its fertilizer effect, initiated carbon dioxide drawdown. Such a drawdown could possibly reduce the greenhouse effect and induce the climate change that led to the Pleistocene glaciations. We estimate that the nitrogen flux enhancement onto the surface from an event at 50 pc would be of order 10%, probably too small for dramatic changes. We estimate deposition of iron (another potential fertilizer) and find it is also too small to be significant. There are also competing effects of opposite sign, including muon irradiation and reduction in photosynthetic yield caused by UV increase from stratospheric ozone layer depletion, leading to an ambiguous result. However, if the atmospheric ionization induces a large increase in the frequency of lightning, as argued elsewhere, the amount of nitrate synthesis should be much larger, dominate over the other effects and induce the climate change. More work needs to be done to clarify the effects on lightning frequency.

Previous article No AccessExtraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago: A ReplyWendy S. Wolbach, Joanne P. Ballard, Paul A. Mayewski, Andrei Kurbatov, Ted E. Bunch, Malcolm A. LeCompte, Victor Adedeji, Isabel Israde-Alcántara, Richard B. Firestone, William C. Mahaney, Adrian L. Melott, Christopher R. Moore, William M. Napier, George A. Howard, Kenneth B. Tankersley, Brian C. Thomas, James H. Wittke, John R. Johnson, Siddhartha Mitra, James P. Kennett, Gunther Kletetschka, and Allen WestWendy S. Wolbach1. Department of Chemistry and Biochemistry, DePaul University, Chicago, Illinois 60614, USA*Author for correspondence; email: [email protected]. Search for more articles by this author , Joanne P. Ballard2. Department of Geography, University of Tennessee, Knoxville, Tennessee 37996-0925, USA Search for more articles by this author , Paul A. Mayewski3. Climate Change Institute, University of Maine, Orono, Maine 04469, USA Search for more articles by this author , Andrei Kurbatov3. Climate Change Institute, University of Maine, Orono, Maine 04469, USA Search for more articles by this author , Ted E. Bunch4. Geology Program, School of Earth Science and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA Search for more articles by this author , Malcolm A. LeCompte5. Center of Excellence in Remote Sensing Education and Research, Elizabeth City State University, Elizabeth City, North Carolina 27909, USA Search for more articles by this author , Victor Adedeji6. Department of Natural Sciences, Elizabeth City State University, Elizabeth City, North Carolina 27909, USA Search for more articles by this author , Isabel Israde-Alcántara7. Instituto de Investigaciones Metalúrgicas, departamento de Geología y Mineralogía, Universidad Michoacana de San Nicolás de Hidalgo, CP 58060, Morelia, Michoacán, Mexico Search for more articles by this author , Richard B. Firestone8. Department of Nuclear Engineering, University of California, Berkeley, California 94720, USA Search for more articles by this author , William C. Mahaney9. Quaternary Surveys, 26 Thornhill Avenue, Thornhill, Ontario L4J 1J4, Canada Search for more articles by this author , Adrian L. Melott10. Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA Search for more articles by this author , Christopher R. Moore11. Savannah River Archaeological Research Program, South Carolina Institute of Archaeology and Anthropology, University of South Carolina, New Ellenton, South Carolina 29809, USA Search for more articles by this author , William M. Napier12. Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, Northern Ireland, United Kingdom Search for more articles by this author , George A. Howard13. Restoration Systems, Raleigh, North Carolina 27604, USA Search for more articles by this author , Kenneth B. Tankersley14. Department of Anthropology and Department of Geology, University of Cincinnati, Cincinnati, Ohio 45221, USA Search for more articles by this author , Brian C. Thomas15. Department of Physics and Astronomy, Washburn University, Topeka, Kansas 66621, USA Search for more articles by this author , James H. Wittke4. Geology Program, School of Earth Science and Environmental Sustainability, Northern Arizona University, Flagstaff, Arizona 86011, USA Search for more articles by this author , John R. Johnson16. Santa Barbara Museum of Natural History, Santa Barbara, California 93105, USA Search for more articles by this author , Siddhartha Mitra17. Department of Geological Sciences, East Carolina University, Greenville, North Carolina 27858, USA Search for more articles by this author , James P. Kennett18. Department of Earth Science and Marine Science Institute, University of California, Santa Barbara, California 93106, USA Search for more articles by this author , Gunther Kletetschka19. Faculty of Science, Charles University, Prague, Czech Republic; Institute of Geology, Czech Academy of Science of the Czech Republic, Prague, Czech Republic; and University of Alaska, 903 Koyukuk Drive, Fairbanks, Alaska 99775, USA Search for more articles by this author , and Allen West20. Comet Research Group, Prescott, Arizona 86301, USA*Author for correspondence; email: [email protected]. Search for more articles by this author PDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 128, Number 1January 2020 Article DOIhttps://doi.org/10.1086/706265 Views: 393Total views on this site Citations: 5Citations are reported from Crossref HistoryReceived August 27, 2019Accepted August 28, 2019Published online December 05, 2019 © 2019 by The University of Chicago. All rights reserved.PDF download Crossref reports the following articles citing this article:William C. Mahaney, Peeter Somelar, Christopher C. R. Allen Late Pleistocene Glacial-Paleosol-cosmic record of the Viso Massif—France and Italy: New evidence in support of the Younger Dryas boundary (12.8 ka), International Journal of Earth Sciences 112, no.11 (Sep 2022): 217–242.https://doi.org/10.1007/s00531-022-02243-9James Lawrence Powell Premature rejection in science: The case of the Younger Dryas Impact Hypothesis, Science Progress 105, no.11 (Jan 2022): 003685042110642.https://doi.org/10.1177/00368504211064272Martin B. Sweatman The Younger Dryas impact hypothesis: Review of the impact evidence, Earth-Science Reviews 218 (Jul 2021): 103677.https://doi.org/10.1016/j.earscirev.2021.103677Francisco Tello, José R. Verdú, Michele Rossini, Mario Zunino Onthophagus pilauco sp. nov. (Coleoptera, Scarabaeidae): evidence of beetle extinction in the Pleistocene–Holocene transition in Chilean Northern Patagonia, ZooKeys 1043 (Jun 2021): 133–145.https://doi.org/10.3897/zookeys.1043.61706Maxim Usatov Main Belt asteroid as a Possible Younger Dryas impactor, Astronomische Nachrichten 341, no.88 (Sep 2020): 734–740.https://doi.org/10.1002/asna.202013817

Ozone in Earth's atmosphere is known to have a radiative forcing effect on climate. Motivated by geochemical evidence for one or more nearby supernovae about 2.6 million years ago, we have investigated the question of whether a supernova at about 50 pc could cause a change in Earth's climate through its impact on atmospheric ozone concentrations. We used the "Planet Simulator" (PLASIM) intermediate-complexity climate model with prescribed ozone profiles taken from existing atmospheric chemistry modeling. We found that the effect on globally averaged surface temperature is small, but localized changes are larger and differences in atmospheric circulation and precipitation patterns could have regional impacts.

The Late Devonian was a protracted period of low speciation resulting in biodiversity decline, culminating in extinction events near the Devonian-Carboniferous boundary. Recent evidence indicates that the final extinction event may have coincided with a dramatic drop in stratospheric ozone, possibly due to a global temperature rise. Here we study an alternative possible cause for the postulated ozone drop: a nearby supernova explosion that could inflict damage by accelerating cosmic rays that can deliver ionizing radiation for up to $\sim 100$ kyr. We therefore propose that the end-Devonian extinctions were triggered by supernova explosions at $\sim 20$ pc, somewhat beyond the "kill distance" that would have precipitated a full mass extinction. Such nearby supernovae are likely due to core-collapses of massive stars; these are concentrated in the thin Galactic disk where the Sun resides. Detecting either of the long-lived radioisotopes Sm-146 or Pu-244 in one or more end-Devonian extinction strata would confirm a supernova origin, point to the core-collapse explosion of a massive star, and probe supernova nucleosythesis. Other possible tests of the supernova hypothesis are discussed.

Deschamps and Mottez (hereafter DM) argue that the Gauss-Matuyama terrestrial magnetic field reversal may have left a vanishing main dipole moment to the field for a time of order 10,000 years. They say this may have allowed an enhanced cosmic ray flux, boosting the effect we proposed in Melott and Thomas (2019). We point out that the bulk of the cosmic ray flux from a nearby supernova should be too energetic, up to a million times more energetic than the limits of deflection by the terrestrial magnetic field. In fact, only those highly energetic ones will directly reach the troposphere, relevant for cloud-to-ground lightning. From Cosmic Explosions to Terrestrial Fires?: A Discussion. F. Deschamps and F. Mottez. J. Geology 128, online ahead of print. (2020) From Cosmic Explosions to Terrestrial Fires?: A Reply A.L. Melott and B.C. Thomas. J. Geology 128, online ahead of print. (2020) From cosmic explosions to terrestrial fires? (A.L. Melott and B.C. Thomas) Journal of Geology, 127, 475-481 10.1086/703418 (2019) [arXiv:1903.01501]

As part of the collaboration between the Trustees and Publishers of the Journal of Horticultural Science and Biotechnology, an annual monetary prize was established for the paper with the most impact published in the previous year. For this prize, the impact is interpreted in its widest sense to include paper views, downloads, citations and Altmetric scores. We are very pleased to announce that the 2019 Journal Prize for the most impactful paper from 2018 (Vol 93) has been awarded to: Sunil Kumar, O. P. Awasthi, A. K. Dubey, Renu Pandey, V. K. Sharma, A. K. Mishra & R. M. Sharma (2018) Root morphology and the effect of rootstocks on leaf nutrient acquisition of Kinnow mandarin (Citrus nobilis Loureiro × Citrus reticulata Blanco), The Journal of Horticultural Science and Biotechnology, 93:1, 100–106, DOI: 10.1080/ 14620316.2017.1345333 We congratulate the authors of the winning paper, which is a multidisciplinary collaboration on Citrus rootstocks between researchers at ICAR-Indian Agricultural Research Institute, New Delhi, India. It is fitting that in its Centenary Year, the Journal of Horticultural Science and Biotechnology Prize should recognise research advances in rootstock science, one of the topics prominent in the first issue of the journal. The prize-winning paper is free to download. To link to this year’s winner: https://www.tandfonline. com/doi/full/10.1080/14620316.2017.1345333

Gene expression profiles provide insight into how microorganisms respond to changing environmental conditions. However, few studies have integrated expression profile analyses of both coding genes and non-coding RNAs (ncRNAs) to characterize the functional activity of microbial community members. Here, we defined gene expression profiles from environmental and laboratory-grown acidophilic biofilms using RNASeq. In total, 15.8 million Illumina reads were mapped to the genomes of 26 acidophilic microorganisms and nine viruses reconstructed from the Richmond Mine at Iron Mountain, California. More than 99% of the genome was transcribed in three Leptospirillum species, and > 80% in the archaea G-plasma and Ferroplasma Type II. High gene expression by G-plasma and the Leptospirillum Group II UBA strain correlated with extremely acidic conditions, whereas high transcriptional expression of Leptospirillum Group III and Leptospirillum Group II 5way-CG strain occurred under higher pH and lower temperature. While expression of CRISPR Cas genes occurs on the sense strand, expression of the CRISPR loci occurs on the antisense strand in the Leptospirilli . A novel riboswitch associated with the biosynthetic pathway for the osmolyte ectoine was upregulated when each specific Leptospirillum Group II strain was growing under the conditions most favorable for it. Newly described ncRNAs associated with CO dehydrogenase (CODH) suggest regulation of expression of CODH as a CO sensor in mature biofilms in the Leptospirilli . Results reveal the ways in which environmental conditions shape transcriptional profiles of organisms growing in acidophilic microbial communities and highlight the significance of ncRNAs in regulating gene expression.IMPORTANCE Microorganisms play important roles in environmental acidification and in metal-recovery based bioleaching processes. Therefore, characterizing how actively growing microbial communities respond to different environments is key to understanding their role in those processes. Microorganisms express their genes, both coding and non-coding, differently depending on environmental factors, thus evaluating community expression profiles inform about the ecology of actively growing microorganisms. Here we used community transcriptomic analyses to characterize gene expression profiles from biofilm communities growing under extremely acidic conditions. Results expand our knowledge of how acidophilic microorganisms respond to changes in their environment and provide insight into possible gene regulation mechanisms.

Plants undergo a series of profound developmental changes throughout their lifetime in response to both external and internal factors. When these changes are abrupt and dramatic, the process is referred to as phase change. The early phase of plant development, during which the plant cannot be induced to flower, has been called the juvenile phase. The juvenile to adult transition within the vegetative phase is associated with several physiological and biochemical markers whilst very little is known about the molecular mechanisms involved in this process. The most striking advances in our understanding of the genetic control of phase transitions have come from the study of vegetative to reproductive phase of inflorescence meristem development in Arabidopsis . During this transition, FLOWERING LOCUS T (FT) mRNA is transmitted from leaf to the shoot apex, where it acts together with FD to activate transcription of floral meristem identity genes, resulting in floral initiation. However, because of its short life cycle, Arabidopsis presents difficulties in juvenile phase studies. On the other hand, Antirrhinum is a plant with a well defined juvenile phase which is affected by light and has a long-day photoperiod requirement similar to Arabidopsis. The major aim of this project is to investigate the reasons for incompetence to flower during the juvenile phase. It is possible to hypothesize that this is due to one or more of the following reasons: The photoperiodic floral induction mechanism that leads to FT expression does not function The apex is not capable of responding to a signal or The signal is not translocated to the apex. Light integral has been found to be a key component of the length of juvenile phase in Antirrhinum ; reduced light levels extend the length of this phase. This may indicate a lack of available photosynthetic assimilates within the transition from juvenile to adult vegetative phase. The effect of irradiance on the accumulation of carbohydrates in leaves and its effect on the transition from juvenile to adult vegetative phase is being studied in Antirrhinum. A method has been developed to detect low-molecular carbohydrates based on the use of HPLC with refractometric detection. Furthermore, an experimental system for determining the length of juvenile phase in Arabidopsis based on reciprocal transfers between long- and short- days has been developed.

Genetic studies aimed at onion improvement have been limited because of high heterozygosity, a very large genome size with a high level of repetitive DNA and a biennial life cycle. Onion bulb initiation is daylength-dependent, which places a significant barrier to adapting new varieties for growth at different latitudes. Compared to the photoperiodic regulation of flowering, relatively little is known about genetic regulation of the bulbing process. This study aims to identify the role of gene sequences involved in daylength-regulated bulb formation and tissue specific expression of onion. A comprehensive set of developmental and spatial quantitative mRNA expression experiments were carried out to investigate expression of onion FLOWERING LOCUS T (AcFT), LEAFY (AcLFY) and GIBBERELLIN-3 OXIDASE (GA3ox1) during the bulbing response. Bulbing ratios were used to measure the response of onion plants under long day (LD) and short day (SD) conditions. AcFT1 was expressed in LD, which induces bulb formation, while AcFT4 was expressed in SD, which inhibits bulb formation. AcFT5 and AcFT6 were expressed in LD and might also be involved in bulb formation itself. All AcFT, AcLFY and GA3ox1 genes showed distinctive patterns of tissue specific expression in onion, with AcFT genes found primarily in the sites of perception in the leaf and LFY in the basal tissues, the site of response. The results are consistent with AcFT1 expression being the signal for LD-induced bulb initiation and AcFT4, being involved in suppressing bulbing in SD.

The end-Permian mass extinction is the most severe known from the fossil record. The most likely cause is massive volcanic activity associated with the formation of the Permo-Triassic Siberian flood basalts. A proposed mechanism for extinction due to this volcanic activity is depletion of stratospheric ozone, leading to increased penetration of biologically damaging Solar ultraviolet-B (UVB) radiation to Earth's surface. Previous work has modeled the atmospheric chemistry effects of volcanic emission at the end-Permian. Here we use those results as input for detailed radiative transfer simulations to investigate changes in surface-level Solar irradiance in the ultraviolet-B, ultraviolet-A and photosynthetically available (visible light) wave bands. We then evaluate the potential biological effects using biological weighting functions. In addition to changes in ozone column density we also include gaseous sulfur dioxide (SO2) and sulfate aerosols. Ours is the first such study to include these factors and we find they have a significant impact on transmission of Solar radiation through the atmosphere. Inclusion of SO2 and aerosols greatly reduces the transmission of radiation across the ultraviolet and visible wavelengths, with subsequent reduction in biological impacts by UVB. We conclude that claims of a UVB mechanism for this extinction are likely overstated.