Identification of a Casparian band in the hypodermis of onion and corn roots

Abstract

The radial walls of the hypodermis in onion and corn roots were impermeable to the apoplastic fluorescent dye Tinopal CBS. All walls of the hypodermis as well as the walls of the epidermis were autofluorescent when viewed under violet light. After clearing with hot NaOH, however, autofluorescence was observed only in the radial walls of the onion and corn hypodermis and in the walls of the onion epidermis. The fluorescence could be intensified by staining with an extract of Chelidonium majus root. The Casparian band of the onion and corn endodermis likewise acted as a barrier to Tinopal CBS diffusion and continued to autofluoresce after treatment with hot NaOH. It is concluded that a Casparian band exists in the hypodermis of onion and corn roots. In the hypodermis the entire radial wall is occupied by the Casparian band. In longitudinal view, the hypodermal Casparian band appears in all the radial and transverse walls of the cells and is continuous from one cell to the neighbouring cells.