Abstract
Tracheary elements (TEs) are differentiated in contact with each other to form a continuous xylem vessel, raising the possibility that cell-cell interaction functions to guide continuous xylem development. We revealed that an arabinogalactan-protein mediates local cell-cell interaction inducing TE differentiation in-vitro. This factor was named as xylogen with reference to its xylogenic activity. In-planta analyses indicated polar localization of xylogen in the apoplast around differentiating TEs and requirement for xylogen of normal vessel development, implying that polarly secreted xylogen draws neighboring cells into the pathway of TE differentiation.
Sulfated-pentapeptide phytosulfokine potently stimulates TE differentiation in-vitro. We revealed that wound-induced phytosulfokine down-regulates wound response in the dedifferentiation process via the suppression of ethylene biosynthesis and protein kinase activities. Taking account of small inhibitory factor(s) balancing with differentiation-inducing factors, we will discuss cell-cell interactions regulating vascular development.
