Impacts of different salt concentrations on the morphology, physiology, and antioxidant properties of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21.

The physiological and biochemical responses of organisms, including cyanobacteria, are greatly influenced by environmental change. Salinity significantly affects global rice output, and cyanobacteria are major contributors to rice productivity. Therefore, in our study, we explore the effects of varying concentrations of three (i.e., MgSO₄, CaCl₂, K₂HPO₄) agriculturally important salts on the biomass, growth, and biochemical status of the rice-field cyanobacterium Nostochopsis lobatus HKAR-21. A significant decrease in the photopigment activity, growth, and effective quantum yield of photosystem II (PSII) (F_v/F_m) was observed in the cells treated with 0 μM K₂HPO₄ and 0 μM MgSO₄. There was minimum effect on the growth and photopigment in samples treated without CaCl₂ (0 μM CaCl₂). Phycobiliproteins (PBPs) and carbohydrate content were largely regulated by MgSO₄. However, K₂HPO₄ had an optimum effect on all three macromolecular components. Brightfield imaging revealed that each salt had a characteristic role in the morphology of the cells. Additionally, in vitro lipid peroxidation with in vivo reactive oxygen species (ROS) and lipid peroxidation were examined with the help of DCFH-DA and Nile red fluorescence, respectively. The antioxidant potential of the carotenoid was checked by using DPPH and ABTS assays. Our study conclusively highlights that the increasing salt concentration will have a negative impact on the cyanobacterium growth which in turn will affect the productivity of rice paddy fields which is one of the most important crops on which more than a billion people are dependent.