Complex bud architecture and cell‐specific chemical patterns enable supercooling of Picea abies bud primordia |
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Authors: | Edith Kuprian Caspar Munkler Anna Resnyak Sonja Zimmermann Tan D Tuong Notburga Gierlinger Thomas Müller David P Livingston III Gilbert Neuner |
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Institution: | 1. Institute of Botany, Unit Functional Plant Biology, University of Innsbruck, Innsbruck, Austria;2. North Carolina State University and USDA‐ARS, Raleigh, NC, USA;3. Department of Material Sciences and Process Engineering, Institute of Wood Science and Technology, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria;4. Department of Nanobiotechnology, Institute for Biophysics, University of Natural Resources and Life Sciences (BOKU), Vienna, Austria;5. Institute of Organic Chemistry, University of Innsbruck, Innsbruck, Austria |
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Abstract: | Bud primordia of Picea abies, despite a frozen shoot, stay ice free down to ?50 °C by a mechanism termed supercooling whose biophysical and biochemical requirements are poorly understood. Bud architecture was assessed by 3D—reconstruction, supercooling and freezing patterns by infrared video thermography, freeze dehydration and extraorgan freezing by water potential measurements, and cell‐specific chemical patterns by Raman microscopy and mass spectrometry imaging. A bowl‐like ice barrier tissue insulates primordia from entrance by intrinsic ice. Water repellent and densely packed bud scales prevent extrinsic ice penetration. At ?18 °C, break‐down of supercooling was triggered by intrinsic ice nucleators whereas the ice barrier remained active. Temperature‐dependent freeze dehydration (?0.1 MPa K?1) caused accumulation of extraorgan ice masses that by rupture of the shoot, pith tissue are accommodated in large voids. The barrier tissue has exceptionally pectin‐rich cell walls and intercellular spaces, and the cell lumina were lined or filled with proteins, especially near the primordium. Primordial cells close to the barrier accumulate di, tri and tetrasaccharides. Bud architecture efficiently prevents ice penetration, but ice nucleators become active inside the primordium below a temperature threshold. Biochemical patterns indicate a complex cellular interplay enabling supercooling and the necessity for cell‐specific biochemical analysis. |
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Keywords: | cell wall pectins extraorgan freezing freeze dehydration ice nucleation stem cells |
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