VIEW ARTICLE

Uptake of the Systemic Fungicide Methyl 2-Benzimidazolecarbamate and the Fluorescent Dye PTS by Onion Roots. Carol A. Peterson, Department of Environmental Biology, University of Guelph, Guelph, Ontario Canada, N1G 2W1; L. V. Edgington, Department of Environmental Biology, University of Guelph, Guelph, Ontario Canada, N1G 2W1. Phytopathology 65:1254-1259. Accepted for publication 6 June 1975. DOI: 10.1094/Phyto-65-1254.

The Casparian band of the endodermis of the root presents a barrier to the uptake of apoplastic chemicals into plants. A possible pathway for entry of apoplastic chemicals is provided by the gaps in the Casparian band caused by the development of secondary roots. The present study tested whether such gaps are necessary for the fungicide MBC (methyl 2-benzimidazolecarbamate) uptake into the plant from a root treatment. Young onion plants sprouted from bulbs were studied since they showed no secondary root development. The lack of pathways allowing indiscriminate passage of apoplastic substances into the onion plant was confirmed experimentally by showing that plants with intact roots were unable to take up a known apoplastic dye PTS (trisodium, 3-hydroxy-5,8, 10-pyrenetrisulfonate). The barrier to PTS penetration was located at the margin of the root, probably in the epidermis. When the outer barrier was mechanically removed, PTS penetrated into the root only as far as the endodermis. In contrast, MBC was readily taken up by onion plants following a treatment of intact roots. Therefore MBC does enter plant roots through the intact endodermis, and also can penetrate the epidermal and hypodermal layers which provide barriers for PTS movement.