Growth and Differentiation of Neurospora Hyphae

Abstract

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.

The role of tip-localized mitochondria in hyphal growth

“…The volume fraction of cytoplasm occupied by mitochondria is highest 5-15 m behind the tip, which was also observed in Neurospora crassa (Lew, 1999). Zalokar (1959) mapped the distribution of mitochondria and mitochondrial biochemical activity in Neurospora, and found that, while mitochondria are located throughout the hyphal apical region (0-150 m), cytochrome oxidase and succinic dehydrogenase, which were identiWed histochemically, are Wrst observed 50 m behind the tip, and increase to a maximal level 100-150 m behind the tip. Of necessity, Zalokar's measurements required Wxation, which may alter the natural distribution of mitochondria.…”

The Morphogenesis and Possible Evolutionary Origins of Fungal Sclerotia

“…Growth of a non-budding strain of C. ulbicuns in sulphur-deficient medium stimulated budding and it was suggested that low availability of sulphur gave greater plasticity to the cell wall. Only a few -SH groups were found in the walls of fungi that form mycelia (Robson & Stockley, 1962) but more were observed near the hyphal tips (Zalokar, 1959; Robson & Stockley, 1962). Pitt (1969) found -SH groups near the tips of phialides of Penicillium notutum but none was detected elsewhere in the walls of this species.…”

Effect of tryptophan on alkaloid biosynthesis in cultures of a Claviceps species

“…This suggests that only mycelium formed in the presence of excess tryptophan is conditioned, at a later stage of development, to a high level of alkaloid synthesis. Although the effect might be attributed to a difference in nutrient uptake between older hyphae and growing tips, studies with other fungi (5,6,36,37) have indicated little distinction between different parts of the mycelium in assimilation and metabolism of amino acids. Tryptophan appears to be taken up readily by growing or resting mycelium of Claviceps strain HLX 123.…”