The activity of powdery-mildew haustoria after feeding the host cells with different sugars, as measured with a potentiometric cyanine dye

Abstract

Abstract. The biotrophic parasite Erysiphe graminisf. sp. hordei produces haustoria within the cells of its host Hordeum vulgare. To determine the physiological activity of these haustoria, the electric potential across the membranes in the mitochondria of the haustorium was studied. The membrane potential was estimated with the fluorescent potentiometric cyanine dye 3,3'-dibutyloxacarbocyanine iodide. The addition of depolarizing agents (carbonylcyanide m-chlorophenylhydrazone, 2,4-dinitrophenol or KCN) to infected cells resulted in an increase of fluorescence after the addition of low concentrations or a decrease of fluorescence after the addition of higher concentrations. When the infected host cell was fed with increasing concentrations of D-glucose (25, 50, 75 raM), corresponding decreases of fluorescence were measured immediately in the mitochondria of the fungal haustoria. Sucrose induced a similar reduction of fluorescence about 20 min later. D-Galactose and D-fructose induced a somewhat smaller reduction of fluorescence, L-glucose and D-glucitol had no effect. The results indicate that haustoria take up glucose from the host cells immediately. Sucrose, D-galactose and D-fructose seem to require time to be metabolized before their products reach the fungal haustorium or mitochondria.

The role of haustoria in sugar supply during infection of broad bean by the rust fungusUromycesfabae

“…Manners (42) suggested that sucrose is the major metabolite absorbed by powdery mildew. Mendgen and Nass (43), and Aked and Hall (44), however, showed that uptake of glucose is more rapid than uptake of sucrose or fructose in powdery mildew. These data are supported by results from Sutton et al (45), indicating that glucose is the major carbon source for powdery mildew.…”

Nutrient uptake in rust fungi: how sweet is parasitic life?

“…With the major plant carbohydrate transport form, sucrose, being diverted directly to the plant pathogen, it seems obvious that the pathogen should try to use this nutrient source and Manners (1989) suggested that sucrose is indeed the major metabolite absorbed by powdery mildews. However, Mendgen and Nass (1988), Aked and Hall (1993), and later Sutton et al (1999) were able to show that D-glucose is a more likely candidate carbohydrate for uptake by powdery mildew fungi. These data together with the substrate specificity determined for HXT1p in U. fabae indicate that it is not sucrose itself which seems to be utilized by the parasite.…”

Plasma Membrane H+-ATPase Activity in Spores, Germ Tubes, and Haustoria of the Rust FungusUromyces viciae-fabae

“…In powdery mildew and rust fungi, haustoria seem to play a major role in this process (Mendgen, 1981;Woods and Gay, 1987;Mendgen and Nass, 1988;Aist and Bushnell, 1991), but the mechanism of metabolite uptake is poorly understood. Active transport of nutrients across the host-haustorial interface has been suggested.…”