The Activity of Invertase and Its Relevance to the Accumulation of Storage Polysaccharides in Leaves Infected by Biotrophic Fungi

SUMMARY Infection of Senecio squalidus by Albugo tragopogonis and of Tussilago farfara and Poa pratensis by Puccinia poarum results in an increase in the activity of an acid invertase localized at the sites of infection. It is concluded that sucrose from the host is first hydrolysed and then absorbed by the parasite. Invertase also plays a key role in the provision of substrate for the typical accumulation of starch around pustules of biotrophic fungi on host species which store this polysaccharide. Compartmentation of invertase and the enzymes concerned with synthesis of sucrose and fructans permits these carbohydrates to be accumulated within pustules on host species which normally store fructans.