The permeability of phi thickenings in apple (Pyrus malus) and geranium (Pelargonium hortorum) roots to an apoplastic fluorescent dye tracer

Abstract

The permeability properties of the phi thickenings in apple (Pyrus malus L.) and geranium (Pelargonium hortorum L. H. Bailey) roots were tested by treating them with a fabric brightener dye, Tinopal CBS-X (disodium-4,4''-bis(2-sulfostyryl)biphenyl). The dye moved apoplastically in the roots of both species and did not penetrate the endodermal layers. In contrast, the dye penetrated the phi thickenings in both types of roots, indicating that phi thickenings do not function as barriers to the apoplastic transport of relatively small molecules.