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Title: Complex bud architecture and cell-specific chemical patterns enable supercooling of Picea abies bud primordial

item KUPRIAN, EDITH - University Of Innsbruck
item MUNKLER, CASPAR - University Of Innsbruck
item RESNYAK, ANNA - University Of Innsbruck
item ZIMMERMANN, SONJA - University Of Innsbruck
item Tuong, Tan
item GIERLINGER, NOTBURGA - University Of Innsbruck
item MULLER, THOMAS - University Of Innsbruck
item Livingston, David
item NEUNER, GILBERT - University Of Innsbruck

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2017
Publication Date: 10/10/2017
Citation: Kuprian, E., Munkler, C., Resnyak, A., Zimmermann, S., Tuong, T.D., Gierlinger, N., Muller, T., Livingston, D.P., Neuner, G. 2017. Complex bud architecture and cell-specific chemical patterns enable supercooling of Picea abies bud primordial. New Phytologist. 40:3101-3112.

Interpretive Summary: When the temperature of water goes below freezing with out becoming ice it is said to be supercooled. Many plants have freezing tolerance mechanisms that allow them to tolerate temperatures below freezing by keeping water in a liquid state. Spruce trees are an extreme example of this mechanism; in fact, buds of spruce are routinely able to remain unfrozen even when the temperature around them is as low as -50C. In this research we identified the specific tissues within the bud that allowed the bud to remain supercooled. We identified this tissue in 3 dimensions and performed several detailed analyses of the tissue to help explain how the plant accomplished this feat. We found individual cells that had significant amounts of pectin and carbohydrates in them. How these compounds helped the bud remain supercooled is discussed in detail in this paper.

Technical 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 extra-organ 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 while the ice barrier remained active. Temperature-dependent freeze dehydration (-0.1 MPa/K) caused accumulation of extra-organ ice masses that by rupture of the shoot pith tissue are accommodated in large voids. The barrier tissue has unrivalled pectin-rich cell walls and spaces, cells near the primordium contained amorphous starch and proteins line cell walls. 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.