Plants are sessile organisms that continue organogenesis throughout the life cycle. This is to adapt to seasonal and environmental changes by modifying their growth and development. They also show remarkable abilities to regenerate from wounding. Every aspect of these processes accompanies vascular connections and re-establishments among tissues and organs. Auxins are plant hormones that are largely produced in young leaves and transported in an oriented manner from shoots to roots. Through this transport, they trigger vascular strand formation in various tissues.
In this lecture, I will introduce a study by Tsvi Sachs in which he examined the effects of artificial auxin sources and of tissue polarities on the course of vascular strand differentiation. Based on the results, he formulated the “canalization hypothesis” in which the flow of auxins reinforces the ability of cells to transport auxin in the same direction. This autocatalytic behaviour of auxin flows has been supported by subsequent molecular genetic studies and is widely accepted to date as the basis of robust vascular connection in plants.