GROWTH AND DIFFERENTIATION OF NEUROSPORA HYPHAE

Zalokar , Marko . (Yale U., New Haven, Conn.) Growth and differentiation of Neurospora hyphae. Amer. Jour. Bot. 46(8): 602–610. Illus. 1959.—Neurospora hyphae grow only at their tips. New protoplasm is formed throughout the hyphae and transported to the tips by active cytoplasmic streaming. This enables the fungus to grow at a prodigious rate. The use of radioactive precursors demonstrated that the rate of protein and ribonucleic acid formation does not decrease substantially in hyphal regions distant from the growing point. Apical growth of hyphae results in a morphological differentiation into young regions filled with cytoplasm and dense with nuclei and old regions, vacuolated and laden with fat droplets. Cytochemical methods were used to study the biochemical differentiation of hyphae and attention was focused on the growing region. It was found that hyphal tips, i.e., the first 50–100 μ of the growing end of the hypha, differed substantially from the rest of the young hyphae. Hyphal tips were slightly richer in proteins and significantly richer in protein-bound sulfhydryl groups and ribonucleic acid. Glycogen was absent at the tips. Peroxidase increased at the tips, while cytochrome oxidase and succinic dehydrogenase decreased. Alkaline phosphatase exhibited strong activity in a short region behind the extreme tip. β-galactosidase, in a few cases, was more active at the tips than in the rest of the hyphae. The results of cytological and cytochemical investigations are discussed in connection with the problem of cellular differentiation.