Written and maintained by CASRAI Editorial Board
Last updated
Short answer: an explant is a piece of living tissue, an organ part or a group of cells taken from an organism and placed on an artificial medium so that it can be cultured. The word is used most in plant tissue culture, but the same term covers animal and human material, and that is where lab-safety rules start to matter.
Definition and scope
The University of Florida’s IFAS plant propagation program defines an explant as “a piece of tissue used to initiate a tissue culture.” The USDA National Agricultural Library Thesaurus words it more broadly: “parts of a living organism, such as cells, tissues, or organs, which are transferred to an artificial medium for culture.” The second definition is the useful one for a lab that works across organisms, because it does not limit the term to plants.
The thesaurus links the concept to four related terms: culture media, micropropagation, propagation materials and totipotency. Together they describe the usual picture. The explant is the starting material, the medium is what it is grown on, and the culture is what the lab ends up with.
How explants are used in practice
In plant work, UF/IFAS reports that explants can be taken from nearly every part of a plant. Stem and leaf sections are the most common choice for micropropagation, and flower parts, roots and seed tissue have also been used. The explant is what starts the culture, so the choice of source tissue is the first decision in any explant-based protocol.
In animal and human work the same logic applies: tissue is removed from the donor and placed in culture. The difference is not the idea but the status of the material, as the next sections explain.
Types and related concepts
The table separates the ways the word and its neighbours are used in the sources above. Every row is taken from a named source.
| Term | What the source says | Source |
|---|---|---|
| Plant explant | A piece of tissue used to initiate a tissue culture; stem and leaf sections are the most common for micropropagation. | UF/IFAS |
| Explant (general) | Cells, tissues or organs of a living organism transferred to an artificial medium for culture. | USDA NAL Thesaurus |
| Primary human cell explant | Primary human cell explants and their in vitro passages (cell “strains”) must be regarded as containing potential bloodborne pathogens. | OSHA interpretation, 21 June 1994 |
| Cell strain | Propagated from primary explants, with a finite lifetime of roughly 20 to 70 passages. | OSHA interpretation, 21 June 1994 |
| Cell line | Immortalised or transformed cells; an established human line characterised as free of hepatitis viruses, HIV and other recognised bloodborne pathogens is not considered OPIM. | OSHA interpretation, 21 June 1994 |
Where it matters for labs: biosafety and the culture medium
Human explants are treated as potentially infectious by default
The text of OSHA’s Bloodborne Pathogens Standard (29 CFR 1910.1030) does not use the word “explant.” It defines other potentially infectious materials (OPIM) to include unfixed human tissue or organs other than intact skin, and HIV-containing cell or tissue cultures, organ cultures, and HIV- or HBV-containing culture medium. How primary explants are handled comes from OSHA’s 21 June 1994 letter of interpretation on human cell lines, which states that all primary human cell explants and their later in vitro passages must be regarded as containing potential bloodborne pathogens, and that all laboratory work with primary human tissues or body fluids is covered by the standard. The interpretation leaves the decision that a cell line is free of bloodborne pathogens to a biosafety professional or other qualified scientist, with the determination kept as a written record. Non-transformed human cell strains can be exempted only when documented laboratory testing shows them free of bloodborne pathogens. Our guide to the Bloodborne Pathogens Standard in research laboratories covers the wider rule, and containment practice is usually described in terms of biosafety levels such as BSL-2.
A checklist of decisions to settle before an explant culture starts
These are decision points rather than procedure steps. Each one maps to a source above.
- Which organism is the donor? The IFAS and NAL definitions both apply, but only human-derived material falls under the OSHA interpretation.
- Which tissue is the explant? For plants, stem and leaf sections are the most common micropropagation sources; flower parts, roots and seed tissue have also been used (UF/IFAS).
- What is it cultured on? The NAL entry ties explants to culture media, so the medium is part of the definition, not an afterthought. See our notes on chemically defined media and the comparison of serum-free and serum-containing media.
- Is the material covered by the Bloodborne Pathogens Standard? For primary human explants and their passages, the OSHA interpretation says yes by default, and a cell line can be excluded only on a documented determination by a qualified person, and non-transformed strains can be exempted only when documented laboratory testing shows them free of bloodborne pathogens.
Common misunderstandings
An explant is not a cell line
An explant is the starting tissue. A cell strain is what is propagated from primary explants and has a finite lifetime. A cell line is immortalised or transformed. The OSHA interpretation treats these differently, so treating an explant culture like an established line such as HeLa is a classification error with safety consequences. Even HeLa, the interpretation says, should be documented as pure HeLa cells and shown to be free of bloodborne pathogens by testing before it is handled outside the standard.
Explants are not only a plant-science term
Plant tissue culture dominates search results, but the NAL definition covers cells, tissues or organs of any living organism.
The rule text does not mention explants
A reader who searches 29 CFR 1910.1030 for the word will not find it. The coverage of primary explants is an OSHA interpretation, so cite the letter and not the rule text when you document it.
FAQ
What are explants?
Explants are pieces of tissue, organ parts or cells from a living organism that are transferred to an artificial medium for culture (USDA NAL Thesaurus).
What is an explant in tissue culture?
It is the piece of tissue used to initiate the culture (UF/IFAS). In plant micropropagation, stem and leaf sections are the most common source.
Are human explants covered by OSHA’s Bloodborne Pathogens Standard?
OSHA’s 21 June 1994 letter of interpretation says primary human cell explants and their later in vitro passages must be regarded as containing potential bloodborne pathogens, and that all laboratory work with primary human tissues or body fluids is covered by the standard. The rule text itself does not use the word “explant”.
Is an explant the same as a cell line?
No. An explant is the starting tissue; a cell strain is propagated from primary explants and has a finite lifetime, while a cell line is immortalised or transformed (OSHA interpretation, 21 June 1994).
Sources
- University of Florida IFAS, Plant Propagation, tissue culture terms: Explant. Checked 2026-10-29.
- USDA National Agricultural Library Thesaurus: Explants. Checked 2026-10-29.
- OSHA, 29 CFR 1910.1030, Bloodborne pathogens. Checked 2026-10-29.
- OSHA, Letter of interpretation, 21 June 1994, Applicability of 1910.1030 to establish human cell lines. Checked 2026-10-29.
