Fig. 4. Binding of green fluorescent‐tagged Ca²⁺ channel blocker, DM‐Bodipy‐DHP, to fresh sections of developing Pistia leaf. (A) Low magnification image. The brightest green fluorescence is associated with Ca oxalate crystal idioblasts at various stages of development (arrows). Some fluorescence is also seen in the young developing mesophyll cells. Red fluorescence is due to chlorophyll. (B) Control. Binding of DM‐Bodipy‐DHP is completely inhibited by a 4‐h pretreatment with the competitive Ca²⁺ channel blocker, nifedipine. Raphide crystal idioblasts (arrows) and druse idioblasts (block arrows) are pointed out for reference. (C) Enlargement from A showing labelled crystal idioblasts. The raphide idioblast to the left (R) is focused through the cortical cytoplasm indicating Ca²⁺ channels are abundant in cytoplasmic organelles. At the large single arrow, the same focal plane is near the surface of the raphide idioblast indicating potential association of the fluorescent probe with the plasma membrane as well. At the double arrow is a cell that is just beginning initiation of differentiation to become a raphide idioblast. Inset is a living raphide crystal idioblast stained with DiOC₆ to show ER abundance. (D) Image of the xylem region of a vein where druse crystal idioblasts are most common. At least four druse idioblasts at various developmental stages are seen and are fluorescing brightly (arrows). Inset is of living druse idioblasts stained with DiOC₆. R, Raphide crystal idioblast; X, xylem. Scale bars: A and B = 50 µm; C and D = 21 µm.