Heat response in the green alga Micrasterias denticulata (Desmidiaceae): Immunodetection and localization of BiP and heat shock protein 70
Weiss, Dagmar; Lütz-Meindl, Ursula
In order to increase our understanding in heat response of fresh water green algae occurrence and distribution of heat shock proteins have been investigated in the green alga Micrasterias denticulata for the first time. Both, heat shock proteins (hsps) hsp70 and BiP (binding protein) have been detected by means of immunoblotting in cells grown at different cultivation temperature (15°C, 20°C, 25°C). Additional heat shock (35°C to 39°C) resulted in an accumulation of hsp70 detectable after cyclic heat treatment (1 h heat shock, 1 h cultivation temperature, repeated 3 times) or after continuous heat exposure (3 to 9 h) increasing with the duration of treatment. Densitometric measurements revealed an increase in hsp70 of about 45 to 155% after continuous heat treatment at different temperature levels and of about 40 to 115% after cyclic heat exposure. Both, the duration of heat exposure and even more important the preceding cultivation temperature were decisive for the intensity of the hsp response. Cells cultivated at 25°C revealed a much weaker heat response than those grown at 20°C or 15°C. The elevated hsp 70 level observed, is due to newly synthesized proteins as protein accumulation is prevented when exposing the cells coincidently to heat and to cycloheximide. We were not able to detect any quantitative increase in BiP levels even after an eight hour continuous treatment. Localization of heat shock proteins by immunogold labeling of ultrathin sections of high pressure frozen Micrasterias cells reveals association of hsp 70 to various vesicle membranes throughout the cytoplasm. In contrast, BiP is detected mostly at a particular population of Golgi vesicles. No free accumulations of heat shock proteins have been observed in the cytoplasm. The distribution of hsps is the same in untreated and heat shocked cells.