Fig. 2

Defining meristematic (MsZ), cell expansion (CEZ), transition (TZ), and cell maturation (MZ) zones of internode 5. a Internode 5 harvested at the half-head emergence developmental stage with its leaf sheath stripped, alongside an equivalent internode 5 where the lower, flexible zone has been bent to display the differentiation between the upper rigid zone and the lower flexible zone. The green line indicates the interface between the flexible and rigid zones of the internode. The harvested meristematic (MsZ—black), cell expansion (CEZ—pink), transitional (TZ—blue), and mature (MZ—orange) zones are indicated. b and c Longitudinal, vibratome cut, 50-μm thick section of the lower region of the internode (indicated by dashed black lines), stained with DAPI and viewed under UV illumination with b, the red chlorophyll emissions isolated, and c, the blue DAPI emissions isolated. Enlarged regions are offset in c, and white scale bars are 50 μm. d Nuclei density and cell size measured using image J were plotted at intervals along the lower region of the internode. e, f and g, Microtome cut 2-μm-thick cross-sections from e, the cell expansion, f, transitional, and g, mature zones, stained with Toluidine blue, counter stained with Lugol’s iodine and imaged using brightfield illumination. Protoxylem (PX), immature vascular bundles (IV), metaxylem (MX), mature vascular bundles (MV), storage parenchyma (SP), and thickened cell walls (TCW) are labelled. Black scale bars in e, f, and g are 100 μm