Loading of Assimilates and Some Sugars Into the Translocation System of Cuscuta

Abstract

Cuscuta species are holoparasitic plants which constitute a strong sink by draining a large proportion of the carbohydrates produced by the host plant. An experimental system has been constructed in order to study the loading of sugars into the translocation system of Cuscuta. Cuscuta campestris parasitizing alfalfa plants were trimmed to one fast-growing shoot on a host stem and allowed to accumulate label from ¹⁴C-labelled assimilates, [¹⁴C]sucrose, sucrose ([¹⁴C]glucose), [¹⁴C]glucose, or 3-O-[¹⁴C]methylglucose supplied to the host stem. Rates of label accumulation were measured and a higher level of sugar accumulated per time unit was interpreted as preferred loading of the sugar. As sucrose was the sugar most rapidly loaded into the translocation system of the parasite, an analogy between this loading mechanism and established cases of phloem loading into leaf veins is suggested.