Distribution and role of mineral compounds in the haustorium of a parasite of Galium arenarium, Thesium humifusum, before flowering

Abstract

The relations between host and parasite in the haustoria of Thesium humifusum have been studied by scanning electron microscopy combined with an energy dispersive system. The distribution of mineral elements in the connecting tissues binding the host and parasite has been determined. It has been shown that the concentrations of phosphorus and potassium were higher in the hyaline tissue and in the intertracheidal parenchyma; the concentration of silicon was higher in the tracheids of the lignified transfer bridge and the concentration of calcium was higher in the cortical parenchyma and secondary phloem of the host root.These results support the existence of an osmotic gradient in the haustorium and between the two partners in the direction of the parasite. This gradient together with the transpiration pull and the intense acid phosphatase activity in the tissues may explain the movement of water and mineral substances from host to parasite.