Phloem Unloading in Stem Parts Parasitized by Cuscuta: The Release of 14C and K+ to the Free Space at 0°C and 25°C

Abstract

AbstractBy washing out 14C‐solutes or K+ from the free space of stem segments of Vicia faba L. and Urtica dioica L., efflux from stem tissues was measured. At 25°C the efflux of 14C or K+ from non‐parasitized stem parts was found to be comparable with the pattern known for parenchyma cells. The efflux pattern from parasitized stem parts kept at 0°C was also a normal one, but at 25°C a more complicated pattern was found. After addition of metabolic inhibitors, however, the efflux pattern appeared to be comparable with the pattern found in 0°C experiments. Also, after washing stem segments for several hours in water at 0°C, Phloem unloading was shown to start unimpeded after transfer to 25°C. Stem parts parasitized by Cuscuta can be regarded as a model system for studying the fundamental processes underlying movement out of sieve tubes in strong sink regions.