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The effect of iron deficiency on heterocyst differentiation and some physiological properties of the filamentous cyanobacterium Anabaena sp. PCC 7120was investigated. Under moderate iron limitation conditions, achieved by addition of iron chelator 2,2′-Dipyridyl (＜80 μmol/L) led to delayed heterocyst differentiation,no heterocyst differentiation was observed under severe iron limitation conditions,when the concentration of 2,2′-Dipyridyl in the medium was more than 100 μmol/L.It seemed that there are certain iron-regulated genes or operons whose function is to control heterocyst development. In addition, iron deficiency impaired the growth.Low-iron cells had a decrease in the quantities of pigment content (chlorophyll and phycocyanin content), the whole cell in vivo absorbance spectra confirmed the de crease, the protein electrophoretic profiles revealed that iron-deficient cells had less protein bands, with the increase of 2,2′ Dipyridyl , the protein bands was more and more less. And differently, iron deficiency also caused an increase of ROS (Reactive Oxygen Species)and SOD activity, it suggests that iron deficiency led to oxidative stress, which generally occured under high-iron conditions.