Epidermal growth factor stimulates type-V collagen synthesis in cultured murine palatal shelves

Abstract. The problem studied was whether treatments that reorient vascular differentiation have a similar effect on the polarity of auxin transport. Hypocotyls of Phaseolus vulgaris L. were cut so that a transverse bridge connected the shoot and root directions. Within three days these bridges of tissue regenerated both vessels and sieve tubes along the new orientation, at 90° to the original axis. Experiments involving organ removal, wounds, and hormone application confirm previous suggestions that this differentiation follows the expected flow of the hormone auxin in the direction of the roots. Transport of (³H) indoleacetic acid through sections in which vascular reorientation occurred was polar: it was at least twice as great in the new direction of the roots than in the opposite direction. This new polarity of transport, at right angles to the original axis of the plant, can be readily understood if there is a positive feed-back between the differentiation of tissue polarity and auxin transport.