Tryptamine: a novel signaling molecule alleviating salt-induced toxicity by enhancing antioxidant defense and PSII photochemistry in Anabaena PCC7120.

Tryptamine, an indoleamine, is recognized as an internal signaling molecule that enables plants to coordinate their responses under environmental stresses. However, its functional role in cyanobacteria remains largely unexplored. Therefore, the present study investigates the regulatory effects of exogenous tryptamine (10 µM) on mitigating salt (NaCl) induced toxicity in nitrogen-fixing cyanobacterium Anabaena sp. PCC7120. Salt (NaCl) at 60 mM markedly impaired growth, reduced photosynthetic pigment contents, suppressed photosynthetic activity including PSII photochemistry while increasing the respiratory rate in Anabaena sp. Further, NaCl also caused a significant rise in oxidative stress biomarkers (O₂·¯, H₂O₂, and malondialdehyde equivalents; MDA). Exogenously applied tryptamine enhanced the salt stress tolerance, leading to an increase in growth, photosynthetic pigment content, photosynthetic efficiency, along with an appreciable rise in antioxidative enzymes (SOD, POD, CAT and GST) that reduced the oxidative damage. Overall, the study signifies the role of tryptamine as a growth promoter substance to salt stressed Anabaena PCC7120 by enhancing the antioxidants defense system that results in better photosynthetic efficiency, increased biomass and increased synthesis of protein. Hence, supplementation of tryptamine can increase the fertility of salt-affected paddy fields, which is a low-input, sustainable agricultural practice. Although tryptamine, a tryptophan-derived monoamine, has been shown to influence cyanobacterial growth and stress responses, there is a need for a deeper understanding of its functions; this study aims to explore its underlying regulatory mechanisms.