Nitric oxide and 5-aminolevulinic acid up-regulate growth, PS II photochemistry and antioxidant activity in UV-B stressed cyanobacterium Nostoc muscorum

Abstract

The signaling molecules 5-aminolevulinic acid (ALA) and nitric oxide (NO) function as growth promoters in plants under abiotic stress. However, their roles in cyanobacteria remain unclear. This work has been attempted to examine the regulatory effects of ALA and NO (sodium nitroprusside; SNP as NO donor) against UV-B toxicity, and to investigate their interaction in regulating these effects in the cyanobacterium Nostoc muscorum ATCC 27,893. UV-B exposure (0.54 Wm−2) significantly reduced light-harvesting pigments, growth, and photosynthesis (PS-II photochemistry and oxygen evolution), while respiration rates increased considerably. Concurrently, oxidative stress biomarkers, including superoxide radical (O2•−), hydrogen peroxide (H2O2) and MDA equivalents (lipid peroxidation products), were substantially increased despite enhanced enzymatic antioxidant activity (glutathione -S- transferase, superoxide dismutase, peroxidase, and catalase). Exogenous ALA and NO mitigated the harmful UV-B impacts, leading to significant improvements in growth, pigment contents, photosynthesis, and normalization of respiration. The ALA and NO treatments further enhanced enzymatic antioxidant activity, resulting in significant reductions in O2•− and H2O2 contents, thereby minimizing UV-B induced damage to cells as evidenced by reduced lipid peroxidation rates. Moreover, supplementation of PTIO (NO scavenger) and L-NAME (NO inhibitor) reversed ALA's mitigating effect, indicating the dependency of ALA on the NO-mediated signaling process to counter UV-B stress in N. muscorum. The study suggests that SNP (NO), being cost-effective, could serve as a potent growth regulator to sustain the growth of N. muscorum, a biological nitrogen fixer and natural inhabitant of paddy fields, enabling sustainable agriculture even under unavoidable UV-B stress conditions.

Keywords

• Chlorophyll a fluorescence kinetics
• Growth
• Oxidative stress
• Signaling molecules
• Sustainable agriculture