Melatonin and salicylic acid synergistically improve arsenic induced oxidative stress tolerance in ornamental sword lily

•As stress triggered oxidative stress and restricted the growth of gladiolus.•The combined application of MT and SA improved the as stress tolerance.•MT+SA increased the level of protein and proline contents.•MT+SA reduced oxidative stress markers via strengthening antioxidant defense system. Arsenic (As) stress hampers the growth and quality of ornamental crops especially cut flowers. However, studies related to the As stress tolerance in ornamental geophytes are scarce in literature. Furthermore, while the individual potential of melatonin (MLT) and salicylic acid (SA) for improving tolerance to metalloid toxicity is well recognised, their combined approach has yet to be investigated, particularly in ornamental cut flowers. This study showed that melatonin and/or salicylic acid improved Gladiolus grandiflorus (cv. Purple Flora) plant tolerance to As toxicity. Arsenic stressed plants had stunted growth, decreased chlorophyll contents, enhanced oxidative stress markers including hydrogen peroxide (H2O2), electrolyte leakage (EL), and malondialdehyde (MDA). Combined application of these protectants had a more pronounced impact in ameliorating the As induced oxidative stress in plants than those of individual application. The findings provide compelling evidence that using MLT in conjunction with SA improves resistance to As toxicity by increasing the activity of enzymatic antioxidants, protein and proline content.