5 Facts On Food Vacuole In Fungi (Formation, Function)

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Food vacuoles are the membrane-bound cell organelle found in unicellular organisms, protists and some fungi too. 

Food vacuoles in fungi are ubiquitous closed sac-like structures, which contain enzymes, secondary metabolites, water etc, bounded by tonoplast. They also have storage capability for nutrients and waste products. They have distinct shapes or sizes due to diverse protein combinations. 

In this article, let us explore more facts about food vacuoles present in fungi.

Which fungi have food vacuoles

Most of the mycorrhizal fungi, pathogenic fungi, saprophytic fungi, and filamentous fungi have food vacuoles for the homeostatic regulation of cytosolic ions and vacuolar biogenesis.  

Paxillus involutus, Phanerochaete velutina, Phialocephala fortinii, Gigaspora margarita, Aspergillus oryzae, Neurospora crassa and several members of the oomycete genus Saprolegnia have prominent food vacuoles in their living hyphae.

Mushrooms, Puffballs, Bracket fungi, Smuts and other yeast cells are having an abundance of food vacuoles. They are primarily involved in metabolite storage and uptake, pH regulation, vacuolar protein sorting and processing etc.

Where are food vacuoles found in fungi?

Food vacuoles are dynamic organelles composed mostly of a single membrane located within eukaryotic cells. Let us see where to find these food vesicles.

Food vacuoles are found inside the cytoplasm of the fungal cells and hyphae of the filamentous fungi performing digestive functions. They store both organic and inorganic substances and are helpful in the detoxification of cells and recycling of macromolecules.

They are also found in algae, protists, and some fungi. They maintain cell size and shape by face-lifting of the plasma membrane through storage, uptake, and elimination as their primary function. Secondary metabolites such as tannins, diterpenes and triterpenes also accumulate in this structure.

How are food vacuoles formed in fungi?

Food vacuoles have a membrane boundary, known as the tonoplast, which serves to separate the cytosolic fluid with an internal matrix. Let us see how they are formed in fungi.

A food vacuole is formed when food is pressed against the membrane, the membrane swells inward until the food particles fit completely inside the cell, causing the cells to separate and form vacuoles.

food vacuole in fungi
Image credit: Action performed by a food vacuole by CNX OpenStax (CC BY 4.0)

They encapsulate ingredients and break them down into simpler forms. When food is digested, nutrients and energy are stored in the cells themselves and absorbed during cellular activity

Food vacuole functions in fungi

Food vacuoles contain cell sap, digestive enzymes and little amount of water. Let us see the wide variety of functions performed by the food vacuoles.

Listed below are the numerous functions performed by food vacuoles:

  1. The food vacuole is important to the cell as it is the major reservoir for certain small molecules and biosynthetic precursors such as basic amino acids and polyphosphates.
  2. Food vacuoles play an essential role in the interaction of secretory and endocytic pathways.
  3. Food vacuoles primarily assist autophagy, as autophagy is a key process in plant pathogens to initiate appressorium formation.
  4. Food vacuoles also maintain the hydrostatic pressure of the cell, giving it an appropriate shape and size.
  5. Food vacuoles help in protection from self-toxicity and also participate in cellular defence mechanisms by forming phagolysosome vesicles.
  6. Food vacuoles are also involved in endocytotic and exocytotic pathways by linking them with lysosomal-vacuolar transport pathways.
  7. Food vacuoles also helps in osmoregulation, cell homeostasis, nutrient transport, regulation of growth across the cell cycle, and death by apoptosis.
  8. Food vacuoles also play an important role in the transportation of solutes like calcium, nitrogenous and phosphorous compounds through fine channels over long distances by peristalsis.
  9. Vacuolar-mediated long-distance nutrient transport systems have also been shown to facilitate mycelial foraging.
  10. Food vacuoles are most helpful in recycling macromolecules during nutrient starvation and the physiology of vegetative growth of the cells.
  11. Food vacuoles not only carry out degradative processes but also serve to eliminate excess water by expulsion.
  12. In the tonoplast membrane, an enzyme V-ATPase creates the driving force for levelling the electrochemical gradient across the membrane.
  13. As fungal vacuoles are acidic compartments that provide a favourable environment for the maturation and activity of hydrolytic enzymes, they play an important role in pH regulation.

These properties of the food vacuoles are the remarkable degree of isolation of mutants having a defect in vacuolar functions with the non-recombinants.

Food vacuole structure in fungi

Food vacuoles are extremely variable in size. They are very complex as this is not only organelle, they work as a motile tubular complex comprising a vacuolar system.

Food vacuoles are comprised of four different zones in some of the hyphal fungi, which work as a complete system. They are given below:

i) Apical zone- which has few or no vacuoles

(ii) Subapical zone- with small ovoid-round vacuoles

(iii) Nuclear sector- in which tubular vacuoles predominate

(iv) Basal sector- where large spherical vacuoles are mostly found.

These parts appear to form a continuous vacuole system with numerous small vesicles connected to other large vesicles and highly tubular regions. Tubules can expand, contract, merge with each other, merge with globular vacuoles, and transform into smaller vesicles. Vesicles can sprout small tubules and appear to glide along large tubules.

Conclusion

In my conclusion, food vacuoles mean empty entity which occupies 80% of the volume in plants and 45% of the fungal cell volume and their main jobs are the storage of nutrients, autophagy, transportation, digestion and protection from deleterious components.

Read more Facts On Food Vacuole In Paramecium.

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