Hormonal Induction of Vascular Differentiation in Cultured Zinnia Leaf Disks

Mesophyll cells differentiated into tracheary elements when Zinnia leaf disks were cultured in media containing sufficient auxin and cytokinin. Moderate increases in the levels of phytohormones induced the recruitment of adjacent cells into the preexisting vasculature, resulting in the “expansion” of leaf veins. Higher hormonal concentrations induced unpatterned differentiation into tracheary elements throughout the mesophyll and epidermis. This novel system should facilitate the study of organized vascular differentiation.