Differential induction of enzymes and antioxidants of the antioxidative defense system in Anabaena doliolum exposed to heat stress

Anabaena doliolum subjected to 43, 48, 53 and 58 degrees C temperature for 1, 2, 3 and 4 h, showed temperature and time-dependent increase in H2O2 production and MDA contents. All the measured enzymes of the antioxidative defense system (SOD, CAT, APX and GR) showed increase in their activities at 43 degrees C after 1 h of treatment, but at higher temperature their activity declined. The content of antioxidants (ASC, GSH, and alpha-TOC) increased significantly with rise in temperature as well as duration of treatment. This study clearly demonstrates that when enzymatic defense system becomes inactive, the antioxidants (GSH, and alpha-TOC) are induced to protect the cyanobacterium from heat stress. One of the major roles of these antioxidants appears to be the protection of PSII as reflected by an effect on O-2 evolution up to 53 degrees C. (c) 2005 Elsevier Ltd. All rights reserved.