Abstract

Cyanobacteria are well known for tolerance toward high level of environmental stresses. They produce several bioactive molecules as a protective measure for survival and growth under abiotic stress. The present study investigates the effect of temperature on cyanobacteria’s ability to produce indole-3-acetic acid (IAA) with tryptophan as a precursor. Three cyanobacterial species, namely, Westiellopsis sp. TPR-29, Hapalosiphon sp. Ryu2-7DN_D3, and Chlorogloeopsis fritschii PCC 6912, were exposed to 15°C, 25°C, 35°C, and 45°C, and its effect on indole-3- acetic production capacity was tested. After 15 days incubation in above temperature, growth (as measured by cell density and chlorophyll A content); biochemical parameters such as carbohydrate, protein, lipids, and extracellular polysaccharide; and stress indicators such as malondialdehyde (MDA), catalase (CAT), and reactive oxygen species (ROS) were examined. Estimates were also made for the production of IAA. Exposure to higher temperature resulted in reduction of growth and macromolecular contents whereas ROS and MDA content increased significantly at 45°C with a concomitant increase in antioxidant enzymes like CAT. Most importantly the IAA content was observed to be higher in non-ambient conditions (15°C, 35°C, and 45°C). Production of IAA at non-ambient temperature indicates that abiotic stress like temperature variations induces phytohormone production in cyanobacterial strains as a defense strategy to protect itself against changing environmental conditions.

Key words: Phytohormones, Indole-3-acetic acid, Temperature, Stress, Tryptophan