Changes on cold hardiness in acclimated and non-acclimated Olea europaea leaves

ARIAS N; BUCCI SJ; SCHOLZ FG; FIEDEROWICKS KOWALL; ASKENAZZI J; GOLDSTEIN G

Buzios

Congreso; Brazilian Congress of Plant Physiology; 2011

Plant cold hardiness is a complex process that involves extrinsic and intrinsic ice nucleating agents, antifreeze proteins, permeability and thickness of the cell wall and anatomical or morphological physical barriers. Like other woody plants Olea europaea undergoes supercooling, a freeze avoidance mechanism to resist frost temperatures during winter. We evaluated sensitive to low temperatures in Olea europaea (var. Arbequina) trees during summer and winter in Patagonian steppe (45¨¬ 47¡¯S, 67¨¬ 30¡¯W). Two- years old- plants were grown outdoor in 20-dm3 pots filled with a mixture of clay and sand soil irrigated bi- weekly. Differential thermal analysis was used to evaluate the temperature at which ice initially form in the central veins of leaves (IN). Electrolyte leakage method was used to evaluate cellular damage of mature leaves and to determine LT50 that is the temperature at which 50% of the total ion leakage was measured. Osmotic potential at turgor loss point (¥÷TLP), bulk elasticity modulus (ɛ), solutes content (Ns) and osmotic potential at full turgor (¥ð0) were estimated from pressure-volume curves. Summer olive leaves showed lowest values of ɛ (2.52 ¡¾0.66 MPa), ¥÷TLP (-4.31¡¾0.13 MPa) and ¥ð0 (-3.06¡¾0.30MPa) than winter olive leaves (ɛ: 4.91¡¾0.18MPa; ¥÷TLP: -1.40¡¾0.89 MPa; ¥ð0: -0.95¡¾1.06MPa). Active osmotically solutes content was lower in acclimated olive leaves (0.242¡¾0.17 mosmol g-1 than in non-acclimated olive leaves (0.728¡¾0.22 mosmol g-1). While IN did not vary between acclimated and non-acclimated leaves (about -7¡ÆC), LT50 values were lower in winter than summer (-6¡ÆC and -3.8¡ÆC respectively). These results suggest that osmotic adjustments observed in summer is a mechanism that could allow olive decrease minimum leaf water potentials to continue extracting water from drier soils within loss turgor. On the other hand, elastic adjustment (more rigid cell wall in acclimated leaves) could contribute to maintain the integrity of the membrane plasmatic and resist frost temperatures during Patagonian winter.