Immunolocalization of zmGRP4. Longitudinal sections of maize primary root tip were incubated with anti-zmGRP4 serum (A, C, and D) or preimmune serum (B). The lateral root-cap region adjacent to the root proper is shown with a higher magnification in C, whereas the root proper region 1 cm distal to the cap is shown in D. Alkaline-phosphatase reactions were done for 1 h in A and B, and for 3 h in C and D. Red arrowheads indicate sloughed-off cap cells. RC, Root cap; RAM, root apical meristem; M, mucilage; RP, root proper; LRC, lateral root cap; Cx, cortex; Ep, epidermis. Scale bars = 100 μm.