Multiple molecular forms of invertase in maize smut infections

Abstract

Following infection of maize seedlings with the maize smut fungus, Ustilago maydis, a progressive increase in the absolute activity of acid invertase was detected over a 16 day period. Activity declined in uninfected seedlings over the same period. This increased activity in infected tissues was correlated with a low sucrose and high hexose content and, presumably, the enzyme serves to provide a supply of hexoses to the growing neoplastic tissues of the host, and to the fungal heterotroph. The major proportion of this increased invertase activity was due to soluble, rather than cell wall-bound enzyme. A single soluble invertase component of mol. wt 100 000 was detected in uninfected tissues by gel electrophoresis and gel filtration. This component was also present in infected tissues but the major activity in these was due to an additional component of mol. wt 145 000. The latter was identical in mol. wt to one of two major invertase components present in cytoplasmic extracts of cultured haploid sporidia of U. maydis. A second major invertase of cultured U. myadis cells (of mol. wt 300 000) was not represented in infected maize tissues. It is suggested that the increased invertase activity of smutted tissue is due to an enzyme of fungal origin, and to a lesser extent, a stimulation of host invertase. These conclusions differ markedly from those reported by other workers using the same host-parasite combination.