The cellular response of three Chlorella species that differ in their temperature preferences and tolerance - Chlorella vulgaris - Antarctic, C. vulgaris strain 8/1 - thermophilic, and Chlorella kesslery - mesophilic - is analysed. Interspecies variability is found for the sensitivity of the species, with respect to the constitutive and induced levels of HSP70B. Based on their sensitivity to heat, the species were ranked as follows: C. vulgaris>C. vulgaris 8/1>C. kesslery. A higher constitutive level and the well-expressed overproduction of HSP70B estimated for C. vulgaris are most likely among the factors that allow it to survive in the extreme Antarctic environment. The overexpression of HSP70B could be characterised as a short-lived stress response as the most pronounced enhancement is measured at 2h after the stress. We also show that HSP70B may be used as a marker of thermal stress in these organisms. Our results contribute to the hypothesis of the conserved functional properties of HSP70B as a mechanism of thermotolerance in plants.
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