title: Freezing resistance in Patagonian woody shrubs: the role of cell wall elasticity and stem vessel size.
abstract: Freezing resistance through avoidance or tolerance of extracellular ice nucleation is important for plant survival in habitats with frequent subzero temperatures. However, the role of cell walls in leaf freezing resistance and the coordination between leaf and stem physiological processes under subzero temperatures are not well understood. We studied leaf and stem responses to freezing temperatures, leaf and stem supercooling, leaf bulk elastic modulus and stem xylem vessel size of six Patagonian shrub species from two sites (plateau and low elevation sites) with different elevation and minimum temperatures. Ice seeding was initiated in the stem and quickly spread to leaves, but two species from the plateau site had barriers against rapid spread of ice. Shrubs with xylem vessels smaller in diameter had greater stem supercooling capacity, i.e., ice nucleated at lower subzero temperatures. Only one species with the lowest ice nucleation temperature among all species studied exhibited freezing avoidance by substantial supercooling, while the rest were able to tolerate extracellular freezing from -11.3 to -20 °C. Leaves of species with more rigid cell walls (higher bulk elastic modulus) could survive freezing to lower subzero temperatures, suggesting that rigid cell walls potentially reduce the degree of physical injury to cell membranes during the extracellular freezing and/or thaw processes. In conclusion, our results reveal the temporal-spatial ice spreading pattern (from stem to leaves) in Patagonian shrubs, and indicate the role of xylem vessel size in determining supercooling capacity and the role of cell wall elasticity in determining leaf tolerance of extracellular ice formation.
authors.affiliation: Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA yongjiangzhang@oeb.harvard.edu goldstein@bio.miami.edu.
authors.forename: Yong-Jiang
authors.initials: YJ
authors.lastname: Zhang
authors.affiliation: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Grupo de Estudios Biofísicos y Eco-fisiológicos (GEBEF), Departamento de Biología, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia 9000, Argentina.
authors.forename: Sandra J
authors.initials: SJ
authors.lastname: Bucci
authors.affiliation: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Grupo de Estudios Biofísicos y Eco-fisiológicos (GEBEF), Departamento de Biología, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia 9000, Argentina.
authors.forename: Nadia S
authors.initials: NS
authors.lastname: Arias
authors.affiliation: Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and Grupo de Estudios Biofísicos y Eco-fisiológicos (GEBEF), Departamento de Biología, Universidad Nacional de la Patagonia San Juan Bosco, Comodoro Rivadavia 9000, Argentina.
authors.forename: Fabian G
authors.initials: FG
authors.lastname: Scholz
authors.affiliation: Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110164, China.
authors.forename: Guang-You
authors.initials: GY
authors.lastname: Hao
authors.affiliation: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, College of Forestry, Guangxi University, Nanning, Guangxi 530004, China.
authors.forename: Kun-Fang
authors.initials: KF
authors.lastname: Cao
authors.affiliation: Department of Biology, University of Miami, PO Box 249118, Coral Gables, FL 33124, USA Departamento de Ecología, Genética y Evolución, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Nuñez, Buenos Aires C1428EGA, Argentina yongjiangzhang@oeb.harvard.edu goldstein@bio.miami.edu.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Goldstein
mesh_terms: D002473:Cell Wall / Q000378:metabolism* / Q000502:physiology; D003080:Cold Temperature; D055119:Elastic Modulus / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology; D018547:Plant Stems / Q000378:metabolism* / Q000502:physiology
keywords: Patagonian steppe; bulk elastic modulus; ice nucleation temperature; leaf lethal temperature; pressure–volume relationship; supercooling