Expression and possible role of stress-responsive proteins in Anabaena

Nitrogen-fixing Anabaena strains offer appropriate model systems to study the cellular and molecular responses to agriculturally important environmental stresses, such as salinity, drought and temperature upshift. Sensitivity to stresses results primarily from reduced synthesis of vital cellular proteins such as phycocyanin and dinitrogenase reductase leading to impairment of photosynthesis and nitrogen fixation. Exposure to stresses induces the synthesis of a large number of general stress proteins and a few unique stress-specific proteins through transcriptional activation of stress-responsive genes. Using a subtractive RNA hybridization approach a large number of osmoresponsive genes have been cloned from Anabaena torulosa. The expression of general stress proteins has been shown to form the basis of adaptation and cross-protection against various stresses in Anabaena. Prominent among such proteins are the K+-scavenging enzyme, KdpATPase, and the molecular chaperone, GroEL. Unlike heterotrophs, carbon starvation does not appear to evoke a global stress response in Anabaena. Supplementation of combined nitrogen or K+ improves inherent tolerance of Anabaena strains to many environmental stresses.