Duringthe evolution organisms are subjected to the continuous impact of environmental factors. In recent years an increasing number of studies have focused on the physicochemical limits of lifeon Earthsuch as temperature, pressure, drought, salt content, pH, heavy metals, etc. Extreme environmental conditions disrupt the most important interactions that support the function and structure of biomolecules.Forthis reason,organisms inhabiting extreme habitats have recently become of particularlygreat interest. Although filamentous fungi are an important partof the polar ecosystem, information about their distribution and diversity, as well as their adaptation mechanisms, is insufficient. In the present study,the fungal strain Penicillium griseofulvum isolated from an Antarctic soil sample was used as a study model. The fungal cellular response against short term exposure to low temperature was observed. Our results clearly showed that short-term low temperature exposure caused oxidative stress in fungal cells and resulted in enhanced level of oxidative damaged proteins, accumulation of reserve carbohydrates and increased activity of the antioxidant enzyme defence. Ultrastructural changes in cell morphology wereanalysed. Different pattern of cell pathology provoked by the application of two stress temperatures was detected. Overall, this study aimed to observe the survival strategy of filamentous fungi in extremely cold habitats, and to acquire new knowledge about the relationship between low temperature and oxidative stress.

Proteases play a key role in cell defense mechanisms to cold-induced oxidative stress. Data on the relationship between cold stress, growth phase, and temperature preferences of the fungal strains isolated from different habitats are very scarce. Here, we report changes in the intra- and extracellular protease activity of three fungal Penicillium strains (two Antarctic and one temperate) under transient temperature downshift during exponential- and stationary growth phases. The results indicated enhanced enzyme levels in both growth phases depending on the degree of stress and strain thermal class. In order to explain the obtained data, we compared them with our previous results on the protein carbonyl content, accumulation of oxidative-stress biomarkers, and antioxidant enzyme defense in the same three fungal strains. The cell response was affected by the temperature preference of the strain, but not by the climatic distance between the locations of isolation.