Figure 1. Polar localization of a maize PIN1 auxin efflux transporter homologue. A maize pinformed1 gene was tagged with the yellow fluorescent protein. Localization of the PIN1 efflux carrier at the lower edge of cells in a file in the vascular tissue of a developing leaf is evident, and marks the presumed directional transport of auxin. Image courtesy of Andrea Gallavotti. Bar, 20 m.

Figure 2. ‘Unloading’ of macromolecules from the phloem into the root apex. In these images, the SUCROSE–H⁺SYMPORTER2 (SUC2) promoter was used to drive specific expression in phloem companion cells of a cell autonomous GFP (a, ‘GFP-ER’, localized to the lumen of the endoplasmic reticulum (ER)) or of a cytoplasmic GFP (b). Note that the ER-localized GFP expression is restricted to the phloem vascular strands, whereas the cytoplasmic GFP exits from the phloem and is transported cell to cell and becomes distributed throughout the root tip. The outline of the root tip in (a) is marked by a white line. Images courtesy of Michelle Cilia.

Figure 3. Graft transmission of a developmental phenotype in tomato. When normal shoots are grafted on to ‘Mouse ears (Me)’ mutant tomato plants (which have a different leaf shape), ‘mouse ear’- shaped leaves start to develop on the normal shoot (marked by ‘*’). This morphological transformation is correlated with movement of the Me mRNA into the normal shoot. See text for details. Reproduced from Plant Cell, 2001, 13:2570 – copyright holder American Society of Plant Biologists.

Figure 4. Evidence that long-range transport of auxin regulates apical dominance. In the plant on the left, growth of the axillary buds formed in the axil of each leaf is suppressed. In the middle image, after the shoot apex is removed, these axillary buds start to grow out as leafy shoots. On the right, application of auxin in an agar block to the decapitated shoot is sufficient to suppress growth of the axillary buds.

Figure 5. Model for the role of FT protein as the systemic flowering signal, florigen. Light period-induced CONSTANS (CO) expression in the leaf phloem companion cells (CC) activates FLOWERING LOCUS T (FT) expression, and FT protein moves into the sieve elements (SE) and is transported (arrows) to the shoot apex. At the apex, FT protein exits the phloem, and forms a complex with FD, leading to transcriptional activation of the floral meristem identity gene APETALA1 (AP1), and the induction of flowers.