Fig. 3. Intercellular localization of SPR2-GFP and SP2L-GFP proteins. (A) SPR2-GFP and SP2L-GFP are expressed under the control of native regulatory elements in spr2-2 and sp2l-1, respectively. Seven-day-old seedlings were analyzed with laser scanning confocal microscopy. (B) SPR2-GFP particles are found at intersections (arrows) of crossing microtubules (marked by dotted lines) in hypocotyl epidermal cells. (C) SPR2-GFP associated with a shrinking microtubule end (arrowheads). (D) SPR2-GFP particles (arrowheads) moved along the microtubule lattice, collided and then merged. (E) SPR2-GFP is abundant at the polymerizing plus end (arrowheads). (F) SPR2-GFP labels cortical microtubules in cotyledon guard cells of 4-day-old seedlings. Three successive micrographs every 16 seconds are shown. The accumulation of SPR2-GFP at the growing microtubule tip is indicated by arrows. (G) Kymograph of SPR2-GFP movement on the yellow line shown in (F).