CHARACTERIZATION OF TEMPERATURE-INDUCED CHANGES IN THE PHOTOSYNTHETICPROPERTIES OF ANACYSTIS-NIDULANS GROWN AT ELEVATED-TEMPERATURE - A DIFFERENTIAL RESPONSE TO HEAT-SHOCK

Photosynthetic properties of high temperature (35 degrees C) grown (HT G)(1) and low temperature (25 degrees C) grown (LTG) cells of Anacysti s were examined. The results revealed several characteristic changes i n the HTG cells which included light absorption property of the pigmen ts, DCMU binding affinity of the photosynthetic apparatus and photosyn thetic yield. There was a time course dependent heat shock (47 +/- 1 d egrees C) induced inhibition of the O-2 evolution in both the types of cells. However, the response of the HTG cells was sluggish as compare d to the LTG cells. Unlike the LTG cells, the heat shock treatment (47 +/- 1 degrees C, 5 min) of the HTG cells did not result into a change in the pigment absorption spectra. The rise kinetics of fluorescence induction curve of chlorophyll a in the presence of DCMU and DCMU + NH 2OH suggested for heat-induced damage to the oxidizing side of photosy stem II in both the HTG and LTG cells. Further, results on the HILL ac tivity in the heat shocked HTG cells showed that the exogenous electro n donors DPC and NH2OH not only retrieved the heat shock induced inact ivation of the HILL activity, but stimulated the rate of activity. On the other hand, the rate of HILL activity in the heat shocked LTG cell s was restored by only NH2OH an electron donor to PSII reaction centre , while DPC-an electron donor to water oxidation complex was ineffecti ve against the heat shock induced inactivation of the electron transpo rt. These results, together, suggested for the presence of less number of heat susceptible sites in the HTG cells than that in the LTG cells , which might be accounting for the high degree of thermostability to the former type of cells.