Abstract: A peptide siderophore, includes one or more N-nitroso-hydroxylamine ligands. The peptide siderophore can include two side chains, each with a N-nitroso-hydroxylamine ligand, and a further side chain with one or more hydroxy carboxylic acid, hydroxamate, catecholate and/or salicylate ligands. The siderophore can be cyclic. A bacterial cell can express the peptide siderophore, and a composition can include the peptide siderophore, for example in the form of its corresponding iron-complex or bacteria. A method for promoting plant growth, promoting root growth or development, improving stress tolerance in a plant, increasing crop yields of a plant, delivering nitric oxide (NO) to a plant, and/or enhancing chlorophyll production in a plant includes administering the peptide siderophore, bacteria expressing the peptide siderophore or a composition including the peptide siderophore to the plant.