Onset Of Acclimation Research Articles

Long- but not short-term heat acclimation produces an apoptosis-resistant cardiac phenotype: a lesson from heat stress and ischemic/reperfusion insults.

Long-term heat acclimation (AC, 30d/34 degrees C) is a phenotypic adaptation leading to increased thermotolerance during heat stress (HS, 2 h 41 degrees C). AC also renders protection against ischemic/reperfusion (I/R, 30' global ischemia/40' reperfusion) insult via cross-tolerance mechanisms. In contrast to the protected AC phenotype, the onset of acclimation (34 degrees C, AC2d) is characterized by cellular perturbations, suggesting increased susceptibility to HS and I/R insults. In this investigation, we tested the hypothesis that apoptosis resistance is part of the AC repertoire and that, at the initial phase of acclimation (AC2d), cytoprotection is impaired. TUNEL staining and caspase 3 levels in HS and I/R insulted hearts affirmed this hypothesis. To examine the role of the mitochondria in life/death decision in AC2d and 30d AC settings vs. control hearts, we studied the Bcl-2 apoptotic cascade and found increased levels of the anti-apoptotic Bcl-X(L) and decreased levels of the pro-apoptotic death promoter Bad in hearts from AC2d and AC animals. In these groups, cytochrome c (cyt c) was elevated in the mitochondria and remained unchanged in the cytosol. This adaptation was insufficient to negate apoptosis in AC2d rats. At this early acclimation phase (and in controls), increased caspase 8 activity confirmed activation of the extrinsic (Fas ligand) apoptosis pathway. In conclusion, the elevated Bcl-X(L)/Bad ratio and decreased cyt c leakage to the cytosol are insufficient to protect the heart and interactions with additional cytoprotective pathways involved in acclimation (elevated HSP70, ROS, and sarcolemmal adaptations to abolish extrinsic apoptosis pathways) are required to induce the apoptosis-resistant AC phenotype.

Influence of Nutrition on Cold Tolerance of ‘Redcoat’ Strawberries1

Abstract Cold stress resistance of ‘Redcoat’ strawberries (Fragaria x ananassa Duch.) grown under several fall fertilization nutrient regimes was determined by artificial freezing. Stress resistance was determined at the onset of acclimation, October 15, and in midwinter with fully hardened plants. The least tolerant plants during the onset of acclimation were those with nutrient deficiencies, those with high N and low P and K and those with a high imbalance of K, whereas the most tolerant plants resulted from fertilizer applications of balanced NPK and balanced NPK plus high P (1:2:1). Fully hardened plants, artificially frozen to -9°C, -11° and -13° crown temperature showed similar stress responses to fertilization except that plants given high N plus P and K were more tolerant than in the October freeze test. Tissue analyses showed that plants with the highest ratio of P/K in crown and root tissues were also the most resistant to cold stress.