Melatonin alleviates iron stress by improving iron homeostasis, antioxidant defense and secondary metabolism in cucumber

•Low-or high-Fe inhibited cucumber growth and induced chlorosis and oxidative stress•Melatonin alleviated oxidative stress and improved photosynthesis under iron stress•Melatonin promoted the activity and transcripts of antioxidant enzymes•Melatonin stimulated biosynthesis of secondary metabolites under iron stress•Melatonin altered Fe uptake and expression of FRO2 and IRT1 under iron stress