The variation in
starch content in healthy and Puccinia striiformsi-infected wheat leaves was measured from 5 to 15 days after inoculation. The
starch content of diseased leaves relative to healthy leaves decreased from 5 to 9 days, increased from 9 to 12 days to twice that of healthy leaves, and decreased from 12 to 15 days after inoculation. Electron micrographs of plant tissues indicated that the
starch accumulated in the chloroplasts of host cells adjacent to fungal hyphae. Variations in
sugar phosphates,
ATP, and
inorganic phosphate were measured during the
infection process.
ADP-glucose pyrophosphorylase was extracted and partially purified from healthy and diseased leaves. When proportionate concentrations of
sugar phosphates and
inorganic phosphate found in healthy and diseased leaves during the
infection process were placed in the assay mixture,
ADP-glucose pyrophosphorylase activity was similar to the pattern of
starch accumulation and was almost the inverse of the variation observed in
inorganic phosphate in diseased leaves during the
infection process. A mechanism to explain the accumulation of
starch is presented and discussed. This mechanism is based on the regulation of
ADP-glucose pyrophosphorylase by changes in effector molecule concentrations during the
infection process. Reasons for these changes are presented.