Trichome: Wikis

  

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Bud and scape of a Stylidium species, displaying the trichomes that can trap and kill insects.

Trichomes (from the Greek τρίχωμα - trikhoma meaning "growth of hair"), are fine outgrowths or appendages on plants and certain protists. These are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae.

Contents

Algal trichomes

Certain—usually filamentous—algae, have the terminal cell produced into an elongate "hair-like" structure called a trichome. The same term is applied to such structures in some cyanobacteria.

Plant trichomes

Aerial surface hairs

Trichomes on Cannabis, rich with THC.
Epiderm of Arabidopsis thaliana with a trichome.
Flower bud of a Capsicum pubescens plant, with many trichomes.

Trichomes on plants are epidermal outgrowths of various kinds. The terms emergences or prickles refer to outgrowths that involve more than the epidermis. This distinction is not always easily applied (see Wait-a-minute tree). Also, there are nontrichomatous epidermal cells that protrude from the surface.

A common type of trichome is a hair. Plant hairs may be unicellular or multicellular, branched or unbranched. Multicellular hairs may have one or several layers of cells. Branched hairs can be dendritic (tree-like), tufted, or stellate (star-shaped).,

A common type of trichome is the scale or peltate hair: a plate or shield-shaped cluster of cells attached directly to the surface or borne on a stalk of some kind.

Any of the various types of hairs may be glandular.

In describing the surface appearance of plant organs, such as stems and leaves, many terms are used in reference to the presence, form, and appearance of trichomes. The most basic terms used are glabrous—lacking hairs— and pubescent—having hairs. Details are provided by:

  • glabrous, glabrate – lacking hairs or trichomes; surface smooth
  • hirsute – coarsely hairy
  • hispid – having bristly hairs
  • downy – having an almost wool-like covering of long hairs
  • pilose – pubescent with long, straight, soft, spreading or erect hairs
  • puberulent – minutely pubescent; having fine, short, usually curly, hairs
  • pubescent – bearing hairs or trichomes of any type
  • strigillose – minutely strigose
  • strigose – having straight hairs all pointing in more or less the same direction as along a margin or midrib
  • villosulous – minutely villous
  • villous – having long, soft hairs, often curved, but not matted

Hairs on plants are extremely variable in their presence across species, location on plant organs, density (even within a species), and therefore functionality. However, several basic functions or advantages of having surface hairs can be listed. It is likely that in many cases, hairs interfere with the feeding of at least some small herbivores and, depending upon stiffness and irritability to the "palate", large herbivores as well. Hairs on plants growing in areas subject to frost keep the frost away from the living surface cells. In windy locations, hairs break-up the flow of air across the plant surface, reducing evaporation. Dense coatings of hairs reflect solar radiation, protecting the more delicate tissues underneath in hot, dry, open habitats. And in locations where much of the available moisture comes from cloud drip, hairs appear to enhance this process.

Root hairs

Root hairs, the rhizoids of many vascular plants, are tubular outgrowths of trichoblasts, the hair-forming cells on the epidermis of a plant root. That is, root hairs are lateral extensions of a single cell and only rarely branched. Just prior to the root hair development, there is a point of elevated phosphorylase activity.

Root hairs vary between 5 and 17 micrometres in diameter, and 80 to 1,500 micrometres in length (Dittmar, cited in Esau, 1965).

Root hairs can survive for 2 to 3 weeks and then die off. At the same time new root hairs are continually being formed at the top of the root. This way, the root hair coverage stays the same.

It is therefore understandable that repotting must be done with care, because the root hairs are being pulled off for the most part. This is why planting out may cause plants to wilt.

See also

References

  • Esau, K. 1965. Plant Anatomy, 2nd Edition. John Wiley & Sons. 767 pp.

External links


Simple English

Trichomes are structures on plant leaves. They may look like hairs but they are not. Trichomes are made of living cells. They stick out from the surface of the leaf.

Trichomes can look very different. Some trichomes have one long cell. Other trichomes are a long chain of cells. Trichomes may have branches which make them look like a star. Trichomes can be very long or very short.

Trichomes help to shade the leaf from the sun. They block too much wind from moving across the leaf surface. This stops too much water from leaving the leaf. Animals might not eat leaves with trichomes because they do not like the taste.

Glandular trichomes have chemicals in them. They break when the leaf is touched. Then the chemicals come out. For example, trichomes on poison ivy leaves have a chemical that makes people itchy.








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