Nitric oxide involved in alleviating iron-deficiency stress in macroalga Gracilariopsis lemaneiformis.

Nitric oxide (NO), an active signaling molecule, plays multifaceted roles in plant growth, development, and responses to biotic/abiotic stresses such as high temperature and nutrient deficiency. In marine environments, algae frequently encounter challenges due to limitations in the availability of essential nutrients, including nitrogen, phosphate and iron. Here, sodium nitroprusside (SNP), a NO donor, was employed to investigate the regulating roles of NO on the physiological traits and metabolic pathways in the iron-deficient macroalga Gracilariopsis lemaneiformis. The supply of SNP mitigated the adverse effect due to iron deficiency by promoting the actual photosynthetic efficiency and photochemical quenching coefficient, NO accumulation, proline content, and ferric chelate reductase (FCR) activity, while reducing the malondialdehyde level, thereby alleviating the algal growth inhibition. After a comparative transcriptome analysis, a total of 1255 upregulated- and 3266 downregulated-unigenes were identified in the SNP-supplied alga relative to the iron-deficient G. lemaneiformis. Furthermore, multiple metabolic pathways were significantly enriched, including photosynthesis, carbon metabolism, phenylpropanoid biosynthesis, nitrogen metabolism, glutathione metabolism, and abscisic acid synthesis and signaling pathway, and the latter three were further demonstrated from the enzyme and metabolite levels. In summary, this study will not only present novel insights into how marine macroalgae adapt to iron-limited environments, but also provide a basis for understanding the crucial role and underlying mechanisms of NO mitigating iron-deficiency adversity in G. lemaneiformis.