CONICET | Buscador de Institutos y Recursos Humanos

Freezing resistance through avoidance or tolerance of extracellularice nucleation is important for plant survivalin habitats with frequent subzero temperatures. Thecoordination between leaf and stem physiological processes under subzerotemperatures and the role of cell walls in leaf freezing resistance is not well-understood.Leaf and stem responses to freezing resistance, leaf bulk elastic modulus, leafand stem supercooling, and stem xylem vessel size of six Patagonian shrubspecies in two sites with different elevation and minimum temperatures (plateauand low elevation sites) were studied. Onlyone species exhibited freezing avoidance by permanent supercooling, while therest were able to tolerate extracellular freezing from -11.3 to -20 oC.Leaves of species with more rigid cell walls (higher bulk elastic modulus) couldsurvive freezing to lower sub-zero temperatures.The negative relationship observed between subzero temperature damage and cellwall elasticity suggest that rigid cell walls reduce the degree of physicalinjure to cell membranes during the extracellular freezing and/or thawprocesses. Shrubs with smaller xylem vessels had greater stem supercooling capacity(ice nucleation occurring at low subzero temperatures in the xylem tissue). Iceseeding was initiated in the stem vessels and quickly spread to the leaves inthe low elevation site, but species growing in the plateau site had barriers toprevent rapid spread of ice. The lower leaf ice nucleation temperatue (INT)than stem INT in the plateau site without impacts on freezing tolerance toextracellular freezing, except in one species growing in both sites, could be aconsequence of adaptive pressures to cope with drought conditions more than tocope with lower air temperatures.

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