1
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Kane CN, McAdam SAM. Spatial and Temporal Freezing Dynamics of Leaves Revealed by Time-Lapse Imaging. PLANT, CELL & ENVIRONMENT 2024. [PMID: 39253967 DOI: 10.1111/pce.15118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2024] [Revised: 07/01/2024] [Accepted: 08/14/2024] [Indexed: 09/11/2024]
Abstract
Freezing air temperatures kill most leaves, yet the leaves of some species can survive these events. Tracking the temporal and spatial dynamics of freezing remains an impediment to characterizing frost tolerance. Here we deploye time-lapse imaging and image subtraction analysis, coupled with fine wire thermocouples, to discern the in situ spatial dynamics of freezing and thawing. Our method of analysis of pixel brightness reveals that ice formation in leaves exposed to natural frosts initiates in mesophyll before spreading to veins, and that while ex situ xylem sap freezes near 0°C, in situ xylem sap has a freezing point of -2°C in our model freezing-resistant species of Lonicera. Photosynthetic rates in leaves that have been exposed to a rapid freeze or thaw do not recover, but leaves exposed to a slow, natural freezing and thawing to -10°C do recover. Using this method, we are able to quantify the spatial formation and timing of freezing events in leaves, and suggest that in situ and ex situ freezing points for xylem sap can differ by more than 4°C depending on the rate of temperature decline.
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Affiliation(s)
- Cade N Kane
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana, USA
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, USA
| | - Scott A M McAdam
- Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana, USA
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2
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Rolle K, Okotrub KA, Evmenova EA, Kuznetsov AG, Babin SA, Surovtsev NV. Reversal of crystallization in cryoprotected samples by laser editing. J Chem Phys 2024; 160:184506. [PMID: 38743430 DOI: 10.1063/5.0206117] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Accepted: 04/29/2024] [Indexed: 05/16/2024] Open
Abstract
Advances in cryobiology techniques commonly target either the cooling or the warming cycle, while little thought has been given to ≪repair≫ protocols applicable during cold storage. In particular, crystallization is the dominant threat to cryopreserved samples but proceeds from small nuclei that are innocuous if further growth is forestalled. To this end, we propose a laser editing technique that locally heats individual crystals above their melting point by a focused nanosecond pulse, followed by amorphization during rapid resolidification. As a reference, we first apply the approach to ice crystals in cryoprotected solution and use Raman confocal mapping to study the deactivation of crystalline order. Then, we examine dimethyl sulfoxide trihydrate crystals that can germinate at low temperatures in maximally freeze concentrated regions, as commonly produced by equilibrium cooling protocols. We show how to uniquely identify this phase from Raman spectra and evidence retarded growth of laser-edited crystals during warming.
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Affiliation(s)
- K Rolle
- Institute of Automation and Electrometry SB RAS, Academician Koptyug av. 1, Novosibirsk 630090, Russia
| | - K A Okotrub
- Institute of Automation and Electrometry SB RAS, Academician Koptyug av. 1, Novosibirsk 630090, Russia
| | - E A Evmenova
- Institute of Automation and Electrometry SB RAS, Academician Koptyug av. 1, Novosibirsk 630090, Russia
| | - A G Kuznetsov
- Institute of Automation and Electrometry SB RAS, Academician Koptyug av. 1, Novosibirsk 630090, Russia
| | - S A Babin
- Institute of Automation and Electrometry SB RAS, Academician Koptyug av. 1, Novosibirsk 630090, Russia
| | - N V Surovtsev
- Institute of Automation and Electrometry SB RAS, Academician Koptyug av. 1, Novosibirsk 630090, Russia
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3
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Stegner M, Buchner O, Geßlbauer M, Lindner J, Flörl A, Xiao N, Holzinger A, Gierlinger N, Neuner G. Frozen mountain pine needles: The endodermis discriminates between the ice-containing central tissue and the ice-free fully functional mesophyll. PHYSIOLOGIA PLANTARUM 2023; 175:e13865. [PMID: 36717368 PMCID: PMC10107293 DOI: 10.1111/ppl.13865] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2022] [Revised: 12/22/2022] [Accepted: 01/23/2023] [Indexed: 05/19/2023]
Abstract
Conifer (Pinaceae) needles are the most frost-hardy leaves. During needle freezing, the exceptional leaf anatomy, where an endodermis separates the mesophyll from the vascular tissue, could have consequences for ice management and photosynthesis. The eco-physiological importance of needle freezing behaviour was evaluated based on the measured natural freezing strain at the alpine treeline. Ice localisation and cellular responses to ice were investigated in mountain pine needles by cryo-microscopic techniques. Their consequences for photosynthetic activity were assessed by gas exchange measurements. The freezing response was related to the microchemistry of cell walls investigated by Raman microscopy. In frozen needles, ice was confined to the central vascular cylinder bordered by the endodermis. The endodermal cell walls were lignified. In the ice-free mesophyll, cells showed no freeze-dehydration and were found photosynthetically active. Mesophyll cells had lignified tangential cell walls, which adds rigidity. Ice barriers in mountain pine needles seem to be realised by a specific lignification patterning of cell walls. This, additionally, impedes freeze-dehydration of mesophyll cells and enables gas exchange of frozen needles. At the treeline, where freezing is a dominant environmental factor, the elaborate needle freezing pattern appears of ecological importance.
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Affiliation(s)
| | - Othmar Buchner
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
| | | | - Jasmin Lindner
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
| | | | - Nannan Xiao
- Institute of Biophysics, University of Natural Resources and Life Sciences (BOKU)ViennaAustria
| | | | - Notburga Gierlinger
- Institute of Biophysics, University of Natural Resources and Life Sciences (BOKU)ViennaAustria
| | - Gilbert Neuner
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
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4
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Stegner M, Flörl A, Lindner J, Plangger S, Schaefernolte T, Strasser A, Thoma V, Walde J, Neuner G. Freeze dehydration vs. supercooling of mesophyll cells: Impact of cell wall, cellular and tissue traits on the extent of water displacement. PHYSIOLOGIA PLANTARUM 2022; 174:e13793. [PMID: 36190477 PMCID: PMC9828361 DOI: 10.1111/ppl.13793] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Revised: 09/26/2022] [Accepted: 09/26/2022] [Indexed: 05/10/2023]
Abstract
The extent of freeze dehydration of mesophyll cells in response to extracellular ice varies from supercooling to severe freezing cytorrhysis. The structural factors involved are poorly understood. In a comparison of mesophyll cells of 11 species, the factors "cell wall", "cellular" and "tissue" traits were investigated. The extent of freeze dehydration was quantified as reduction in the sectional area during controlled freezing in the presence of ice. The cell wall thickness, cell size, cell area and the relative area of intercellular spaces were determined. The modulus of elasticity was determined by psychrometry. To grasp the relationships between factors and with freeze dehydration, we applied a principal component analysis. The first two components explain 84% of the variance in the dataset. The first principal component correlated negatively with the extent of freeze dehydration and relative area of intercellular spaces, and positively with the squared cell wall thickness to cell size ratio, elasticity and cell wall thickness. The cell size parameters determined the second principal component. Supercooling appeared preferable in cells with a high squared cell wall thickness to cell size ratio and a low relative area of intercellular spaces. Such factors are hypothesised to affect the magnitude of negative turgor pressure being built up below the turgor loss point. Negative turgor pressure slows dehydration by reducing the water potential gradient to the extracellular ice. With high levels of freeze dehydration, sufficient intercellular spaces for extracellular ice accommodation are needed. The low relative area of intercellular spaces increases cell-to-cell contact area and could support tissue stability.
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Affiliation(s)
| | | | - Jasmin Lindner
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
| | | | | | | | - Viktoria Thoma
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
| | - Janette Walde
- Department of StatisticsUniversity of InnsbruckInnsbruckAustria
| | - Gilbert Neuner
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
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5
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Kaplenig D, Bertel C, Arc E, Villscheider R, Ralser M, Kolář F, Wos G, Hülber K, Kranner I, Neuner G. Repeated colonization of alpine habitats by Arabidopsis arenosa viewed through freezing resistance and ice management strategies. PLANT BIOLOGY (STUTTGART, GERMANY) 2022; 24:939-949. [PMID: 35833328 PMCID: PMC9804731 DOI: 10.1111/plb.13454] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Accepted: 06/15/2022] [Indexed: 05/17/2023]
Abstract
Success or failure of plants to cope with freezing temperatures can critically influence plant distribution and adaptation to new habitats. Especially in alpine environments, frost is a likely major selective force driving adaptation. In Arabidopsis arenosa (L.) Lawalrée, alpine populations have evolved independently in different mountain ranges, enabling studying mechanisms of acclimation and adaptation to alpine environments. We tested for heritable, parallel differentiation in freezing resistance, cold acclimation potential and ice management strategies using eight alpine and eight foothill populations. Plants from three European mountain ranges (Niedere Tauern, Făgăraș and Tatra Mountains) were grown from seeds of tetraploid populations in four common gardens, together with diploid populations from the Tatra Mountains. Freezing resistance was assessed using controlled freezing treatments and measuring effective quantum yield of photosystem II, and ice management strategies by infrared video thermography and cryomicroscopy. The alpine ecotype had a higher cold acclimation potential than the foothill ecotype, whereby this differentiation was more pronounced in tetraploid than diploid populations. However, no ecotypic differentiation was found in one region (Făgăraș), where the ancient lineage had a different evolutionary history. Upon freezing, an ice lens within a lacuna between the palisade and spongy parenchyma tissues was formed by separation of leaf tissues, a mechanism not previously reported for herbaceous species. The dynamic adjustment of freezing resistance to temperature conditions may be particularly important in alpine environments characterized by large temperature fluctuations. Furthermore, the formation of an extracellular ice lens may be a useful strategy to avoid tissue damage during freezing.
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Affiliation(s)
- D. Kaplenig
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
| | - C. Bertel
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
| | - E. Arc
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
| | | | - M. Ralser
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
| | - F. Kolář
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
- Department of BotanyCharles University of PraguePragueCzech Republic
| | - G. Wos
- Department of BotanyCharles University of PraguePragueCzech Republic
| | - K. Hülber
- Department of Botany and Biodiversity ResearchUniversity of ViennaViennaAustria
| | - I. Kranner
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
| | - G. Neuner
- Department of BotanyUniversity of InnsbruckInnsbruckAustria
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6
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Solanki T, García Plazaola JI, Robson TM, Fernández Marín B. Freezing induces an increase in leaf spectral transmittance of forest understorey and alpine forbs. Photochem Photobiol Sci 2022; 21:997-1009. [PMID: 35226331 DOI: 10.1007/s43630-022-00189-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Accepted: 02/10/2022] [Indexed: 10/19/2022]
Abstract
Evergreen plants growing at high latitudes or high elevations may experience freezing events in their photosynthetic tissues. Freezing events can have physical and physiological effects on the leaves which alter leaf optical properties affecting remote and proximal sensing parameters. We froze leaves of six alpine plant species (Soldanella alpina, Ranunculus kuepferi, Luzula nutans, Gentiana acaulis, Geum montanum, and Centaurea uniflora) and three evergreen forest understorey species (Hepatica nobilis, Fragaria vesca and Oxalis acetosella), and assessed their spectral transmittance and optically measured pigments, as well as photochemical efficiency of photosystem II (PSII) as an indicator of freezing damage. Upon freezing, leaves of all the species transmitted more photosynthetically active radiation (PAR) and some species had increased ultraviolet-A (UV-A) transmittance. These differences were less pronounced in alpine than in understorey species, which may be related to higher chlorophyll degradation, visible as reduced leaf chlorophyll content upon freezing in the latter species. Among these understorey forbs, the thin leaves of O. acetosella displayed the largest reduction in chlorophyll (-79%). This study provides insights into how freezing changes the leaf optical properties of wild plants which could be used to set a baseline for upscaling optical reflectance data from remote sensing. Changes in leaf transmittance may also serve to indicate photosynthetic sufficiency and physiological tolerance of freezing events, but experimental research is required to establish this functional association.
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Affiliation(s)
- Twinkle Solanki
- Organismal and Evolutionary Biology (OEB), Viikki Plant Science Centre (ViPS), Faculty of Biological and Environmental Sciences, University of Helsinki, 00014, Helsinki, Finland
| | - José Ignacio García Plazaola
- Department of Plant Biology and Ecology, University of the Basque Country (UPV/EHU), Barrio Sarriena s/n, 48940, Leioa, Spain
| | - T Matthew Robson
- Organismal and Evolutionary Biology (OEB), Viikki Plant Science Centre (ViPS), Faculty of Biological and Environmental Sciences, University of Helsinki, 00014, Helsinki, Finland.
| | - Beatriz Fernández Marín
- Department of Botany, Ecology and Plant Physiology, University of La Laguna (ULL), 38200, Tenerife, Spain
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7
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Steiner P, Buchner O, Andosch A, Holzinger A, Lütz-Meindl U, Neuner G. Winter survival of the unicellular green alga Micrasterias denticulata: insights from field monitoring and simulation experiments. PROTOPLASMA 2021; 258:1335-1346. [PMID: 34304308 PMCID: PMC8523418 DOI: 10.1007/s00709-021-01682-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Accepted: 06/09/2021] [Indexed: 06/13/2023]
Abstract
Peat bog pools around Tamsweg (Lungau, Austria) are typical habitats of the unicellular green alga Micrasterias denticulata. By measurement of water temperature and irradiation throughout a 1-year period (2018/2019), it was intended to assess the natural environmental strain in winter. Freezing resistance of Micrasterias cells and their ability to frost harden and become tolerant to ice encasement were determined after natural hardening and exposure to a cold acclimation treatment that simulated the natural temperature decrease in autumn. Transmission electron microscopy (TEM) was performed in laboratory-cultivated cells, after artificial cold acclimation treatment and in cells collected from field. Throughout winter, the peat bog pools inhabited by Micrasterias remained unfrozen. Despite air temperature minima down to -17.3 °C, the water temperature was mostly close to +0.8 °C. The alga was unable to frost harden, and upon ice encasement, the cells showed successive frost damage. Despite an unchanged freezing stress tolerance, significant ultrastructural changes were observed in field-sampled cells and in response to the artificial cold acclimation treatment: organelles such as the endoplasmic reticulum and thylakoids of the chloroplast showed distinct membrane bloating. Still, in the field samples, the Golgi apparatus appeared in an impeccable condition, and multivesicular bodies were less frequently observed suggesting a lower overall stress strain. The observed ultrastructural changes in winter and after cold acclimation are interpreted as cytological adjustments to winter or a resting state but are not related to frost hardening as Micrasterias cells were unable to improve their freezing stress tolerance.
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Affiliation(s)
- Philip Steiner
- Department of Biosciences, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria
- Institute of Pharmacology, University of Linz, Huemerstrasse 3-5, 4020, Linz, Austria
| | - Othmar Buchner
- Department of Biosciences, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria.
| | - Ancuela Andosch
- Department of Biosciences, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria
| | - Andreas Holzinger
- Department of Botany, Functional Plant Biology, University of Innsbruck, Sternwartestrasse 15, 6020, Innsbruck, Austria
| | - Ursula Lütz-Meindl
- Department of Biosciences, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria
| | - Gilbert Neuner
- Department of Botany, Functional Plant Biology, University of Innsbruck, Sternwartestrasse 15, 6020, Innsbruck, Austria
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8
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Bertel C, Hacker J, Neuner G. Protective Role of Ice Barriers: How Reproductive Organs of Early Flowering and Mountain Plants Escape Frost Injuries. PLANTS (BASEL, SWITZERLAND) 2021; 10:plants10051031. [PMID: 34065614 PMCID: PMC8161042 DOI: 10.3390/plants10051031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Revised: 05/17/2021] [Accepted: 05/19/2021] [Indexed: 05/29/2023]
Abstract
In the temperate zone of Europe, plants flowering in early spring or at high elevation risk that their reproductive organs are harmed by episodic frosts. Focusing on flowers of two mountain and three early-flowering colline to montane distributed species, vulnerability to ice formation and ice management strategies using infrared video thermography were investigated. Three species had ice susceptible flowers and structural ice barriers, between the vegetative and reproductive organs, that prevent ice entrance from the frozen stems. Structural ice barriers as found in Anemona nemorosa and Muscari sp. have not yet been described for herbaceous species that of Jasminum nudiflorum corroborates findings for woody species. Flowers of Galanthus nivalis and Scilla forbesii were ice tolerant. For all herbs, it became clear that the soil acts as a thermal insulator for frost susceptible below ground organs and as a thermal barrier against the spread of ice between individual flowers and leaves. Both ice barrier types presumably promote that the reproductive organs can remain supercooled, and can at least for a certain time-period escape from effects of ice formation. Both effects of ice barriers appear significant in the habitat of the tested species, where episodic freezing events potentially curtail the reproductive success.
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Affiliation(s)
- Clara Bertel
- Department of Botany, University of Innsbruck, Sternwartestrasse 15, 6020 Innsbruck, Austria;
| | - Jürgen Hacker
- Hechenbichler GmbH, Cusanusweg 7-9, 6020 Innsbruck, Austria;
| | - Gilbert Neuner
- Department of Botany, University of Innsbruck, Sternwartestrasse 15, 6020 Innsbruck, Austria;
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9
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Steiner P, Buchner O, Andosch A, Wanner G, Neuner G, Lütz-Meindl U. Fusion of Mitochondria to 3-D Networks, Autophagy and Increased Organelle Contacts are Important Subcellular Hallmarks during Cold Stress in Plants. Int J Mol Sci 2020; 21:E8753. [PMID: 33228190 PMCID: PMC7699614 DOI: 10.3390/ijms21228753] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Revised: 11/12/2020] [Accepted: 11/14/2020] [Indexed: 12/25/2022] Open
Abstract
Low temperature stress has a severe impact on the distribution, physiology, and survival of plants in their natural habitats. While numerous studies have focused on the physiological and molecular adjustments to low temperatures, this study provides evidence that cold induced physiological responses coincide with distinct ultrastructural alterations. Three plants from different evolutionary levels and habitats were investigated: The freshwater alga Micrasterias denticulata, the aquatic plant Lemna sp., and the nival plant Ranunculus glacialis. Ultrastructural alterations during low temperature stress were determined by the employment of 2-D transmission electron microscopy and 3-D reconstructions from focused ion beam-scanning electron microscopic series. With decreasing temperatures, increasing numbers of organelle contacts and particularly the fusion of mitochondria to 3-dimensional networks were observed. We assume that the increase or at least maintenance of respiration during low temperature stress is likely to be based on these mitochondrial interconnections. Moreover, it is shown that autophagy and degeneration processes accompany freezing stress in Lemna and R. glacialis. This might be an essential mechanism to recycle damaged cytoplasmic constituents to maintain the cellular metabolism during freezing stress.
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Affiliation(s)
- Philip Steiner
- Department of Biosciences, Faculty of Natural Sciences, University of Salzburg, Hellbrunnerstraße 34, A-5020 Salzburg, Austria; (O.B.); (A.A.); (U.L.-M.)
| | - Othmar Buchner
- Department of Biosciences, Faculty of Natural Sciences, University of Salzburg, Hellbrunnerstraße 34, A-5020 Salzburg, Austria; (O.B.); (A.A.); (U.L.-M.)
| | - Ancuela Andosch
- Department of Biosciences, Faculty of Natural Sciences, University of Salzburg, Hellbrunnerstraße 34, A-5020 Salzburg, Austria; (O.B.); (A.A.); (U.L.-M.)
| | - Gerhard Wanner
- Ultrastructural Research, Department Biology I, Faculty of Biology, Ludwig-Maximilians-University, Großhadernerstraße 2−4, Planegg-Martinsried, D-82152 Munich, Germany;
| | - Gilbert Neuner
- Department of Botany, Functional Plant Biology, Faculty of Biology, University of Innsbruck, Sternwartestraße 15, A-6020 Innsbruck, Austria;
| | - Ursula Lütz-Meindl
- Department of Biosciences, Faculty of Natural Sciences, University of Salzburg, Hellbrunnerstraße 34, A-5020 Salzburg, Austria; (O.B.); (A.A.); (U.L.-M.)
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10
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Stegner M, Lackner B, Schäfernolte T, Buchner O, Xiao N, Gierlinger N, Holzinger A, Neuner G. Winter Nights during Summer Time: Stress Physiological Response to Ice and the Facilitation of Freezing Cytorrhysis by Elastic Cell Wall Components in the Leaves of a Nival Species. Int J Mol Sci 2020; 21:E7042. [PMID: 32987913 PMCID: PMC7582304 DOI: 10.3390/ijms21197042] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 09/21/2020] [Accepted: 09/21/2020] [Indexed: 01/01/2023] Open
Abstract
Ranunculus glacialis grows and reproduces successfully, although the snow-free time period is short (2-3 months) and night frosts are frequent. At a nival site (3185 m a.s.l.), we disentangled the interplay between the atmospheric temperature, leaf temperatures, and leaf freezing frequency to assess the actual strain. For a comprehensive understanding, the freezing behavior from the whole plant to the leaf and cellular level and its physiological after-effects as well as cell wall chemistry were studied. The atmospheric temperatures did not mirror the leaf temperatures, which could be 9.3 °C lower. Leaf freezing occurred even when the air temperature was above 0 °C. Ice nucleation at on average -2.6 °C started usually independently in each leaf, as the shoot is deep-seated in unfrozen soil. All the mesophyll cells were subjected to freezing cytorrhysis. Huge ice masses formed in the intercellular spaces of the spongy parenchyma. After thawing, photosynthesis was unaffected regardless of whether ice had formed. The cell walls were pectin-rich and triglycerides occurred, particularly in the spongy parenchyma. At high elevations, atmospheric temperatures fail to predict plant freezing. Shoot burial prevents ice spreading, specific tissue architecture enables ice management, and the flexibility of cell walls allows recurrent freezing cytorrhysis. The peculiar patterning of triglycerides close to ice rewards further investigation.
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Affiliation(s)
- Matthias Stegner
- Department of Botany, University of Innsbruck, 6020 Innsbruck, Austria; (B.L.); (T.S.); (A.H.); (G.N.)
| | - Barbara Lackner
- Department of Botany, University of Innsbruck, 6020 Innsbruck, Austria; (B.L.); (T.S.); (A.H.); (G.N.)
| | - Tanja Schäfernolte
- Department of Botany, University of Innsbruck, 6020 Innsbruck, Austria; (B.L.); (T.S.); (A.H.); (G.N.)
| | - Othmar Buchner
- Department of Biosciences, University of Salzburg, 5020 Salzburg, Austria;
| | - Nannan Xiao
- Institute for Biophysics, University of Natural Resources and Life Sciences (BOKU), 1190 Vienna, Austria; (N.X.); (N.G.)
| | - Notburga Gierlinger
- Institute for Biophysics, University of Natural Resources and Life Sciences (BOKU), 1190 Vienna, Austria; (N.X.); (N.G.)
| | - Andreas Holzinger
- Department of Botany, University of Innsbruck, 6020 Innsbruck, Austria; (B.L.); (T.S.); (A.H.); (G.N.)
| | - Gilbert Neuner
- Department of Botany, University of Innsbruck, 6020 Innsbruck, Austria; (B.L.); (T.S.); (A.H.); (G.N.)
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