Springer Nature is making Coronavirus research free. View research | View latest news | Sign up for updates

Ultrastructure of ascospore delimitation in freeze substituted samples ofAscodesmis nigricans (Pezizales)

  • 34 Accesses

  • 23 Citations


Freeze substitution proved to be a valuable technique for studying the early stages of ascosporogenesis inAscodesmis nigricans. Our observations indicate that the ascus vesicle originated from the ascus plasma membrane. Invaginations of the plasma membrane produced ascus vesicle initials consisting of two closely spaced unit membranes. The appearance of the outer leaflet of each of these membranes was identical to that of the inner leaflet of the ascus plasma membrane. Apparent points of continuity between ascus vesicle initials and the plasma membrane were observed. Ascus vesicle initials accumulated in the ascus cytoplasm near the plasma membrane and then coalesced to form the ascus vesicle, a peripheral, cylinder-like structure consisting of two closely spaced unit membranes that extended from the ascus apex to the ascus base. The ascus vesicle then became invaginated in a number of regions and subsequently gave rise to eight sheet-like segments, or ascosporedelimiting membranes, that encircled uninucleate segments of cytoplasm forming ascospore initials. Like the ascus vesicle, each ascospore-delimiting membrane consisted of two closely spaced unit membranes, the inner of which became the ascospore plasma membrane. The ascospore wall then developed between the spore plasma membrane and the outer membrane. Many details of ascospore maturation were clearly visible in freeze substituted samples.

This is a preview of subscription content, log in to check access.


  1. Beckett A (1981) Ascospore formation. In: Turian G, Hohl HR (eds) The fungal spore: morphogenetic controls. Academic Press, New York, pp 107–129

  2. Brummelen J, van (1989) Ultrastructure of the ascus and the ascospore wall inEleutherascus andAscodesmis (Ascomycotina). Persoonia 14: 1–17

  3. Carroll GC (1967) The ultrastructure of ascospore delimitation inSaccobolus kerverni. J Cell Bio 33: 218–224

  4. — (1969) A study of the fine structure of ascosporogenesis inSaccobolus kerverni. Arch Mikrobiol 66: 321–339

  5. Dyby SD, Kimbrough JW (1987) A comparative ultrastructural study of ascospore ontogeny in selected species ofPeziza (Pezizales; Ascomycetes). Bot Gaz 148: 283–296

  6. Gibson JL, Kimbrough JW (1988 a) Ultrastructural observations on Helvellaceae (Pezizales). Ascosporogenesis of selected species ofHelvella. Can J Bot 66: 771–7783

  7. — — (1988 b) Ultrastructural observations on Helvellaceae (Pezizales). II. Ascosporogenesis ofGyromitra esculenta. Can J Bot 66: 1743–1479

  8. Harper RA (1897) Kerntheilung und freie Zellbildung in Ascus. Jahrb Wiss Bot 30: 249–284

  9. Hoch HC (1986) Freeze-substitution of fungi. In: Aldrich HC, Todd WJ (eds) Ultrastructure techniques for microorganisms. Plenum, New York, pp 183–212

  10. Howard RJ (1981) Ultrastructural analysis of hyphal tip cell growth in fungi: Spitzenkörper, cytoskeleton and endomembranes after freeze-substitution. J Cell Sci 48: 89–103

  11. —, Aist JR (1979) Hyphal tip cell ultrastructure of the fungusFusarium: improved preservation by freeze-substitution. J Ultrastruct Res 6: 224–234

  12. —, O'Donnell KL (1987) Freeze substitution of fungi for cytological analysis. Exp Mycol 11: 250–269

  13. Kimbrough JW, Gibson JL (1990) Ultrastructural and cytological observations of apothecial tissues ofGeopyxis carbonaria (Pezizales, Ascomycetes). Can J Bot 68: 243–257

  14. Merkus E (1973) Ultrastructure of the ascospore wall in Pezizales (Ascomycetes) -I.Ascodesmis microscopica (Crouan) Seaver andA. nigricans van Tiegh. Persoonia 7: 351–366

  15. Mims CW, Richardson EA, Roberson RW (1988) Ultrastructure of freeze-substituted and chemically fixed basidiospores ofGymnosporangium juniperi-virginianae. Mycologia 80: 356–364

  16. Moor H (1987) Theory and practice of high pressure freezing. In: Steinbrecht RA, Zierold K (eds) Cryotechniques in biological electron microscopy. Springer, Berlin Heidelberg New York Tokyo, pp 175–191

  17. Müller M, Moor H (1984) Cryofixation of thick specimens by high pressure freezing. In: Revel J-P, Barnard T, Haggis HG (eds) The science of biological specimen preparation for microscopy and microanalysis. Proceedings 2nd Pfefferkorn Conference. AMF O'Hare, Chicago, pp 131–138

  18. Oso BA (1969) Electron microscopy of ascus development inAscobolus. Ann Bot 33: 205–209

  19. Reeves F (1967) The fine structure of ascospore formation inPyronema domesticum. Mycologia 59: 1018–1033

  20. Reynolds, ES (1963) The use of lead citrate at high pH as an electronopaque stain in electron microscopy. J Cell Biol 17: 208–221

  21. Rowley CR, Moran DT (1975) A simple procedure for mounting wrinkle-free sections on formvar-coated slot grids. Ultramicroscopy 1: 151–155

  22. Samuelson DA (1978 a) Asci of the Pezizales. I. The apical apparatus of iodine positive species. Can J Bot 56: 1860–1865

  23. — (1978 b) Asci of the Pezizales. II. The apical apparatus of representatives in theOtidia — Aleuria complex. Can J Bot 56: 1876–1904

  24. — (1978 c) Asci of the Pezizales. III. The apical apparatus of eugymnohymenial representatives. Amer J Bot 65: 748–758

  25. — (1978 d) Asci of the Pezizales. VI. The apical apparatus ofMorchella esculenta, Helvella crispa, andRhizina undulata. General discussion. Can J Bot 56: 369–3082

  26. Schrantz J-P (1967) Etude cytologique, en microscopie optique et électronique, de quelques Ascomycétes. I. Le noyau. Rev Cytol Biol Vég 33: 1–100

  27. Wells K (1972) Light and electron microscopic studies ofAscobolus sterorarius. II. Ascus and ascospore ontogeny. Univ Calif Pub Bot 62: 1–93

  28. Welter K, Müller M, Mendgen K (1988) The hyphae ofUromyces appendiculatus within the leaf tissue after high pressure freezing and freeze substitution. Protoplasma 147: 91–99

Download references

Author information

Correspondence to C. W. Mims.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Mims, C.W., Richardson, E.A. & Kimbrough, J.W. Ultrastructure of ascospore delimitation in freeze substituted samples ofAscodesmis nigricans (Pezizales). Protoplasma 156, 94–102 (1990). https://doi.org/10.1007/BF01666510

Download citation


  • Ascodesmis nigricans
  • Ascosporogenesis
  • Freeze substitution fixation
  • Ultrastructure