Biochemical and histochemical localization of invertase in Neurospora crassa during conidial germination and hyphal growth.

The intracellular localization of Neurospora invertase, an enzyme partially secreted and partially retained by Neurospora at the cell periphery, was investigated. A cell wall fraction was isolated, to which 24% of the cell-bound invertase was firmly attached. A sensitive osmiophilic stain for invertase was developed and used in conjunction with the technique of indirect immunofluorescence to follow the pattern of invertase localization during the development of Neurospora from the germination of conidia to the mature hypha. These studies revealed that: (i) conidial invertase was uniformly distributed along the cell periphery; (ii) growing hyphal tips of germinating conidia showed pronounced invertase activity as the rest of the conidial cell wall lost its peripheral activity; (iii) hyphae in early log-phase growth had strong enzyme activity associated with the cell wall, and in late log phase the activity became associated with the plasma membrane and points where new hyphal branches were being formed; and (iv) hyphae in early stationary phase had strong fluorescence at incipient branching points, in "dots" close to the plasma membrane, and in the cytoplasm.