The active role of the host (Vicia faba L.) in the transfer of nutrient elements from the phloem to the parasite (Cuscuta species): Metabolically controlled K+ and Mg++ release to the free space

By washing out potassium and magnesium from the free space of stem segments of Vicia faba, parasitised stem parts were shown to have an efflux pattern different from that of normal ones. Using the graphical method of compartmental analysis it could be shown that the K+ and Mg++ efflux from parasitised stem parts does not occur in accordance with the regularities displayed by non-parasitised stem parts and known for other higher plant tissues. The process causing the different efflux pattern is apparently under metabolic control since it appeared to be inhibited at 0°C and after addition of 2,4-dinitrophenol or sodium azide. The possibility is discussed that the increased efflux is at least partly caused by an enhanced unloading rate for K + and Mg++ by the host phloem as was shown in a previous study for 14C-solutes.