Leaf seasonal accumulation of a 47-kDa dehydrin and changes in its cryoprotective activity in Nothofagus dombeyi (Mirb.) Blume Acumulación estacional de una deshidrina de 47-kDa en hojas y cambios en su actividad crioprotectora en Nothofagus dombeyi (Mirb.) Blume

Nothofagus dombeyi (Mirb.) Blume is an evergreen tree, pioneer in habitats subject to unfavorable environmental conditions as nighttime freezing temperatures and low water content. It inhabits zones characterized by cold Winter with freezing temperature and Spring frosts reaching to -5°C. Furthermore, it has the capacity to maintain a functional photosynthetic apparatus at low temperatures. We postulated that N. dombeyi is capable to accumulate dehydrins in leaves in response to cold. Seasonal variation in dehydrins, soluble total proteins, and cryoprotective activity in vitro of protein extracts of N. dombeyi leaves were analyzed during the years 2004 and 2005. A dehydrin-like protein of 47-kDa was immunologically identified; this protein was present only in Winter and Spring. The highest accumulation of this protein and the maximal in vitro cryoprotective activity was found during Spring. The leaf total protein extract of this season preserved the 100% of lactate dehydrogenase (LDH) enzyme activity after 5 freeze/thaw cycles in liquid nitrogen adding 10 μg/ml of total proteins extract. The soluble protein concentration increased from 1.8 mg/g in Summer to 4.8 mg/g in Fall on base of fresh weight, and declined through Winter and Spring. The 47-kDa dehydrin may be related to cold hardiness of leaf tissue in overwintering N. dombeyi. We conclude that cell dehydration caused by freezing is the main factor involved in the triggering of 47-kDa dehydrin accumulation in leaves of N. dombeyi. The accumulation of reactive oxygen species (ROS) by oxidative stress product of high irradiance and frosts during Spring, and their role in the triggering of the 47-kDa dehydrin accumulation in leaves of N. dombeyi is discussed. Nothofagus dombeyi (Mirb.) Blume es un árbol siempreverde, pionero en sitios con condiciones ambientales desfavorables como baja temperatura nocturna y baja disponibilidad hídrica. Habita en zonas caracterizadas por inviernos fríos con temperaturas congelantes y heladas de primavera que pueden llegar a los -5°C. Además tiene la capacidad de mantener su aparato fotosintético funcional en condiciones de baja temperatura. Postulamos que N. dombeyi es capaz de acumular deshidrinas en sus hojas en respuesta a baja temperatura. Se analizó la variación estacional de deshidrinas, proteínas solubles totales y la actividad crioprotectora in vitro de extractos proteicos de hojas de N. dombeyi durante los a os 2004 y 2005. Una proteína con características de deshidrina de 47 kDa de peso molecular fue identificada inmunológicamente en hojas, la que estuvo pres