An electron microscopical study of the development of peroxisomes during formation and germination of ascospores in the methylotrophic yeast Hansenula polymorpha

Abstract

Ascospore formation was studied in liquid cultures of the yeast Hansenula polymorpha, previously grown under conditions in which the synthesis of alcohol oxidase was repressed (glucose as growth substrate) or derepressed (methanol, glycerol and dihydroxyacetone as growth substrates and after growth on malt agar plates). In ascospores obtained from repressed cells, generally one small peroxisome was present. The organelle probably originated from the small peroxisome, originally present in the vegetative cells. They had no crystalline inclusions and cytochemical experiments indicated the presence of catalase, urate oxidase and amino acid oxidase activities in these organelles. In ascospores obtained from derepressed cells, generally 1--3 crystalline peroxisomes were observed. These organelles also originated from the peroxisomes originally present in the vegetative cells by means of fragmentation or division. They contained, in addition to the enzymes characteristic for peroxisomes in spores from repressed cells, also alcohol oxidase. The latter enzyme is probably responsible for the crystalline substructure of these peroxisomes. Peroxisomes had no apparent physiological function in the process of ascosporogenesis. A glyoxysomal function of the organelles during germination of the ascospores was also not observed. Germination of mature ascospores in media containing different sources of carbon and nitrogen showed that the function of the peroxisomes present in ascospores of Hansenula polymorpha is probably identical to that in vegetative haploid cells. They are involved in the oxidative metabolism of different carbon and nitrogen sources. Their enzyme profile is a reflection of that peroxisomes of vegetative cells and their presence may enable the formation of cells which are optimally adapted to environmental conditions extant during spore germination.

Regulation of the yeast SPS19 gene encoding peroxisomal 2,4‐dienoyl‐CoA reductase by the transcription factors Pip2p and Oaf1p: β‐oxidation is dispensable for Saccharomyces cerevisiae sporulation in acetate medium

“…Peroxisomes are known to play a role during both sporulation and germination in filamentous fungi (listed in Veenhuis et al, 1980). More recent studies of the link between peroxisomes and karyogamy in these fungi have led to the finding that Podospora anserina car1 mutants lacking peroxisomes were defective for nuclear fusion, a process required for sexual sporulation (Berteaux-Lecellier et al, 1995).…”

“…Pioneering work on the methylotrophic yeast, Hansenula polymorpha, indicated that peroxisomes have no apparent physiological function during ascosporogenesis and that their function during subsequent germination was equivalent to that in vegetative cells, where they facilitate the cells' adjustment to environmental factors (Veenhuis et al, 1980). We provide here molecular evidence indicating that no Pip2p-and Oaf1p-dependent genes are required for sporulation on acetate medium and, using a ⌬pox1 strain and peroxisome-defective ⌬pex6 mutants, we have demonstrated for the first time that ␤-oxidation and the peroxisomal compartment containing it are dispensable for S. cerevisiae development to proceed on this carbon source.…”

Growth of Candida famata and Trichosporon cutaneum on uric acid as the sole source of carbon and energy, a hitherto unknown property of yeasts

“…Their absence in glucose-grown cells suggests that these organelles are involved in carbon and/or nitrogen metabolism. Since urate oxidase, the key enzyme in aerobic uric acid metabolism, is a typical peroxisomal enzyme, which is for instance present in yeast peroxisomes during growth of cells on uric acid as the nitrogen source (Veenhuis et al, 1980), these organelles most probably are peroxisomes. Yeast peroxisomes have been shown to be the site of several enzymes involved in the catabolism of carbon and nitrogen compounds, e.g.…”

Fate and role of peroxisomes during the life cycle of the yeast Saccharomyces cerevisiae : inheritance of peroxisomes during meiosis

“…Peroxisomes in germinating spores of H. polymorpha have been postulated to enable the cells to rapidly respond to environmental changes following sexual development, whereas in filamentous fungi peroxisomes play a key role during exit from quiescence (Veenhuis et al 1980;Berteaux-Lecellier et al 1995). We completed the survey of the S. cerevisiae life cycle by monitoring germinating spores for peroxisome induction.…”

“…Sporulation in S. cerevisiae includes premeiotic DNA replication, high-frequency recombination followed by the two meiotic divisions, and culminates in ascospore formation during which the four haploid nuclei are packaged into spores in an ascus (Esposito and Klapholz 1981;Dawes 1983). Peroxisomes proliferate during karyogamy, sporulation, and germination in filamentous fungi (Berteaux-Lecellier et al 1995), however, only a single, small peroxisome occurs in ascospores of the methylotrophic yeast Hansenula polymorpha (Veenhuis et al 1980).…”