FIT NBs induced by blue light and a standardized FIT NB analysis procedure was developed to analyze the characteristics and dynamics of FIT NBs (supports Fig. 1 ). (A) Induction of FIT NBs in Arabidopsis root epidermis cells of the root differentiation zone at t = 0 and t = 40 min of 5-d-old seedling (2x35S_pro:FIT-GFP) grown under iron deficiency. FIT-GFP signals were evenly distributed in the nucleus at t = 0 min, and after induction by excitation with 488 nm laser NB formation accumulated in NBs at t = 40 min. Root epidermis cells developed few NBs with weak FIT-GFP signals, sometimes taking up to 2 h to appear. Representative pictures from four independent experiments. (B)Arabidopsis root epidermal cells of the root differentiation zone of 5-d-old seedling (proFIT:FIT-GFP) grown under iron deficiency do not show NBs when taken directly from white light. Representative pictures from three independent experiments. Scale bar: 2 µm. (C) Experimental steps for FIT NB induction in transiently transformed N. benthamiana leaf epidermis cells. Fluorescence protein expression was induced by β-estradiol (“induction of protein expression”) 16 h prior to imaging and measurements. Leaf discs were excised, and initial fluorescence images and measurements were taken (“data acquisition t = 0”). Leaf discs were exposed to 488 nm laser light as a light trigger for 1 min (“light induction of NB formation”), and 5 min later, fluorescence images and measurements were taken again (“data acquisition t = 5”). With this procedure, FIT NBs were visible, and their characteristics could be analyzed. In some cases, fluorescence images and measurements were taken at t = 15 min, as indicated in the text. Imaging was performed at the respective wavelengths for detection of GFP and mRFP/mCherry, respectively. Figure C has been created with the help of https://BioRender.com.