Forms and accumulation of iron at rice root tip

To explore the forms and accumulation of iron at root tips in rice (Oryza sativa L.) under Fe2+ toxicity stress, iron-tolerant rice variety “9308” was germinated under laboratory conditions and the seedlings were treated with various Fe²⁺ concentrations (0~400 μmol·L^-1). The content and forms of iron at 0~10 mm root tips were measured via Flame Atomic Absorption Spectrometric and sequential extraction. Under 400 μmol·L^-1 Fe²⁺ stress, iron content in 0~2 mm root tip is highest, while that in root border cells increases with increasing Fe²⁺ concentration. The order of contents of various forms of iron in primary root is Fe-Mn oxide combined form > residual form > organometallic compound > exchangeable form> carbonate-bound form. This finding indicates that the 0~2 mm rice root tip is the main acting site of Fe²⁺ toxicity. Most of the irons are tightly bounded in the 0~10 mm root tip. This reduces iron phyto-availability, enabling root border cells to fix up excessive Fe²⁺.