Sustained synthesis of the bps1 mobile compound requires post-embryonic root growth. The top row shows wild type seedlings with their broad flat leaves and highly interconnected leaf veins, and bps1-2 mutants, with their very small radial leaf primordia and incomplete primary vein. The second row shows the effect of BSO-induced root arrest on wild type and bps1 mutants. In the wild type, shoots of BSO-grown plants had chlorotic cotyledons and small leaves with modestly reduced vein patterns. The shoots of bps1-2 mutants growth on BSO-containing media produced two types of leaves: the first leaf pair (black arrow) were elongated but radial, and contained only a single vein, while leaves that arose later were broad, flat, and produced more complex vein patterns. The third row shows rml1-1 and bps1-2 rml1-1 double mutants. The rml1-1 mutants were slightly smaller than the wild type and they produced slightly narrow, pointed leaves with modestly reduced patterns of veins. The bps1-2 rml1-1 double mutants produced two types of leaves: the first leaf pair (black arrow) were radialized but elongated, and contained a single vein, while later leaves were broad, flat, and produced complex vein patterns. Size bars: 500 μm.