Carbohydrate Metabolism in Healthy and Rusted Leaves of Coltsfoot

Abstract

Summary Infection of leaves of Tussilago by Puccinia poarum results in decreased export of photosynthetic products and, when infection is severe, in increased import. Photosynthetic products move to infection sites where host metabolites are converted to specific fungal products, including mannitol, arabitol, trehalose, glycogen, glucomannan and lipids. More previously fixed 14C is translocated to the fungus in the dark than in the light since, in the dark, degradation of starch contributes to net movement of 14C.

QUANTITATIVE DETERMINATION OF STARCH AND GLYCOGEN AND THEIR METABOLISM IN LEAVES OF TUSSILAGO FARFARA DURING INFECTION BY PUCCINI A POARUM

“…As described by Holligan et al (1974), sucrose is translocated rapidly to within the pustule and is assimilated by the fungus. This process continues in the dark so that, by 23 h, more than 50% of the ^'C fixed by the diseased discs is in fungal metabolites.…”

“…During the 3 h in ^^^002 in the light, ^*C is assimilated by host tissue mainly into sucrose and a-glucan (Holligan et al, 1974). Values here were 60% and 25% respectively.…”

“…However, soluble glycogen levels remain high and, after 20 h, its specific activity rises to 13 d/min/fig. As the percentage radioactivity in host glucans declines, that in glycogen does not rise significantly (Table 3) since there is concomitant incorporation of ^"^C into the soluble fraction as mannitol, arabitol and trehalose are synthesized (Holligan et al, 1974). In addition to glycogen, the only other insoluble glucan which incorporates substantial amounts of radioactivity is a glucomannan, probably a structural component of fungal cell walls .…”

“…Radioactivity in sucrose also declines (Holligan et al, 1974). Much of the radioactivity is either lost as respiratory CO2 or redistributed into structural polymers (discarded in the final residue, see Fig.…”

“…The a-glucan from host tissue gives a black colour with iodine and is considered to be a starch which is partly soluble in water and which is a primary product of photosynthesis. Although fructans accumulate in leaf tissue in much larger amounts (>2ooo figlcm^ within pustules of P. poarum ), they incorporate little or no label during ^^COj experiments of this type (Holligan et al., 1974) and are apparently a secondary product of carbon dioxide fixation.…”