Development, Types, Functions and Microscopy
Trichomes is the term used to refer to tiny
outgrowths from the plant epidermis. Although the term "trichomes"
generally refers to outgrowths ranging from small hairs to larger outgrowths
like thorns, it is typically used to refer to the tiny hairs that can be seen
emerging from the surfaces of leaves and other epidermal surfaces of plants.
They are either unicellular or multicellular (epidermal cells), which means
that some require a microscope to take a closer look.
** The word trichome originated from the Greek
word "Trichoma" that refers to hair growth.
Recent studies suggest that these cells
differentiate from a pool of equivalent cells. This means that like other
cells, they differentiate with the growth of the plant and become specialized
cells that serve a number of functions important to the plant.
and specialization of these cells is largely regulated by a number of
transcription factors which include the R2R3 MYB, basic helix-loop-helix
protein and WD40 repeat protein among others.
These developmental factors,
among others, are responsible for regulating the parts of the plant where the
trichomes will develop as well as the number of trichomes for a given plant.
For instance, whereas the miR156 causes ectopic trichomes to develop on such parts as the floral organs of a plant, high expression of SPL, a resistant form of
miR156 results in reduced reduction of trichomes.
Such regulation varies from
one plant to another.
Some of the other factors that regulate the development
and differentiation of trichomes include:
- phytohormones - regulate
the differentiation process
- cytokinins - influence
increased formation of trichomes
- jasmonic acid and salicylic
acid - these acids contribute to the formation of these cells in Arabidopsis
(small flowing plants found in Eurasia)
Types of Trichomes
As unicellular and multicellular epidermal appendages, there are a variety of trichomes that exist. These vary in size, morphology, origin as well as where they are located and the ability to secrete.
While the classification of trichomes has been found to be somewhat challenging, they are categorized as follows:
Glandular and Non-Glandular Trichomes
Trichomes are either glandular or non-glandular.
These types of trichomes are known to secrete
various substances including water, nectar, resins, mucilage and terpens among
others. Apart from their capacity to secrete, glandular trichomes can also be
grouped in accordance to the number of cells.
* Glandular trichomes is the term used to refer
to an array of glands.
Glandular trichomes not only vary in the type of
substances they secrete and their location, but also with regards to the mode
through which they produce these secretions.
There are both unicellular and
multicellular glandular trichomes. Moreover, they can also be uniseriate (they
are arranged in single series or layer) or multiseriate (arranged in several
Unicellular glandular - For these types of hairs,
it's possible to see morphological differences between apical and basal part
of the cells. They may also occur branched or un-branched.
Multicellular glandular trichomes - these types of trichomes
appear as outgrowths of the epidermis with a head consisting of cells that
secrete and store great amounts of specialized metabolites.
The glandular trichomes include the stinging
hairs and glandular hairs. The Urtica dioica is a good example of plants that have
stinging hairs. The hairs of these plants have in place a basal bulb that gives
rise to a protruding stiff and slender structure. The hairs are capable of
secreting a poisonous substance that can irritate the skin when people come in
contact with the plant and the sharp hair part penetrates the skin.
As for the glandular
hairs (unicellular and multicellular) they can produce a variety of substances
including oils and resins which makes them important in various industries
Examples of glandular trichomes include:
- Saltbush (Atriplex)
- Docks and Sorrels (secretes
- Basil plants (secretes
For the glandular trichomes, there are a wide
variety of secretions that are produced by various plants. For this reason,
glandular trichomes can be classified on the basis of the type of substances
that they secrete. The following is one of the classifications that have been
suggested with regards to secretions:
Unmodified or slightly modified substances -
This includes such substances as salts and nectar
Substances that are synthesized by constituent
cells - This includes:
- Hydrophilic substances
- Stinging hairs
- Lipophilic substances
* One of the main weaknesses of this method of
classification is that there are glandular hairs that are capable of secreting a
variety of substances.
non-glandular trichomes vary in anatomy, morphology and microstructure. Despite
this diversity, they are mostly grouped on the basis of their morphology.
the glandular trichomes, non-glandular trichomes also exist as either
unicellular or multicellular. However, they can also exist as either branched
or un-branched. A majority of these have been shown to be branched, simple and
shaped like a star. As for the un-branched non-glandular trichomes, they can
exist as uniseriate, biseriate or multiseriate. They also vary in shape, size
and length and can be found in a variety of plants.
Different types of non-glandular trichomes can
be found in different locations of a single plant. For instance, whole some of
these can be found on the leaf of the plant (unicellular non-glandular
trichomes on Coridothymus capitatus) two-celled trichomes can be located at the
base of abaxial side of the leaf.
The following are examples of non-glandular
- Gossypium with vesicular
- T- shaped Corokia
There different types of trichomes that serve
different functions for plants. There functions are largely dependent on the
type of trichome as well as their location on the plant. While the function of
some trichomes remains unknown, we will look at some of the known functions of
Like animals, plants have also evolved over
time. This has seen plants developing a range of mechanism for protection. This
enhances the life span of the plant and ensures their survival.
some of the means through which some plants protect themselves from animals,
extreme environmental conditions and thus enhancing their chances of survival. For
instance, the trichomes (glandular) that develop in cannabis plants secrete a
bitter substance and a strong aroma that prevents some animals from eating it.
In particular, some glandular hairs tend to secrete lipophilic substances that
prevent animals from consuming the leaves of the plant.
Apart from chemicals
that wade off animals and pathogens, some trichomes secrete a type of mucilage
that serves to trap insects when they come in contact with the plant leaves.
This substance also helps prevent excessive water loss from the leaves as well
as protecting the plant from excessive moisture. The non-glandular trichomes develop to
form a thick and dense surface around the leaves which serves to protect leaves
and the plant in general from harsh environmental conditions as well as
protection from pathogens.
With some plants such as Tragia cannabina stinging
hairs develop to protect the plant from herbivores. When an animal comes in
contact with the hair, they break off and penetrate the body of the animal
Absorption of Water and Moisture
Non-glandular trichomes can also be found in the
roots of the plant as hair-like structures where they support the absorption of
water and other minerals required by the plant. These trichomes are more likely
to exist as tubular structures that grow outwards to absorb water and minerals
from the soil. However, they are very small with a thin cell wall, and thus can
not last long. Once they die, they become lignified and are unable to absorb
water and minerals any longer. However, new ones continue to form.
In some of
the plants (such as apples and sorghum) the unicellular hairs can secrete
mucilaginous droplets, which ensures that the plant does not dry out.
Therefore, ensuring that the plant can survive for longer.
Some of the other functions of trichomes include:
- Elimination of excess toxic
substances and salts from such plants as the Atriplex
- Waxes protect plants from
extreme heat and sunlight
- Oils from such plants as
Cymbopogon act as insect repellent,
- Protection of developing
buds by such trichomes as the Ephemeral trichomes
Also referred to as cannabis, marijuana is a
plant that contains a mind altering substance. Recent studies have shown that
certain chemicals from the plant have medicinal benefits for various patients.
Like a number of other plants, trichomes develop on the plant when it starts
growing and develop fully when the plant starts flowering.
For marijuana, the
trichomes exist as resin glands that produce various oils that protect the
plant by acting as deterrents. At the same time, these substances protect the
plant from extreme conditions and fungal growth.
There are three types of
trichomes that develop in the cannabis plant. These include:
- Bulbous trichomes - These trichomes appear
as small pointed structures on the surface of the plant. They are the smallest
trichomes and are responsible for secreting resins.
- Capitate-sessile - This type of trichomes
is bigger compared to bulbous trichomes and tend to develop before the plant
starts flowering. They are flattened and contain cannabinoids.
- Capitate stalked trichomes - These are the largest of
the three types of trichomes and form during flowering. They are largely
involved in the synthesis of cannabinoids and terpenoid synthesis.
Given that some of the trichomes
(capitate-stalked trichomes) in marijuana contain the substance that produces
the psychoactive effect, they influence the time of harvesting.
coloration of the glandular heads of the trichomes rather than the amount of
trichomes is the determining factor for harvesting.
Using a microscope, it's
possible to view the head of the capitate-stalked glandular trichomes. This coloration varies between
different marijuana strains as well as depending on the maturity stage of the
As the concentration peak of THC (Tetrahydrocannabinol) nears, trichomes
have a translucent coloration. This color is the result of trichome glands
producing the resin. However, the levels of CBD (Cannabidiol) is still low at
this point. At the same time, the aromatic molecules are also at their
In most cases, the plant
leaves are harvested when the head of the glandular trichome starts turning
opaque. And so there is a higher level of THC that can produce the best
While some trichomes can be seen with the naked
eye (as hairs and spikes) others are too small that they require a microscope
to see and study them. A range of microscopes can be used to view trichomes and
identify the differences in their shapes and sizes etc.
* Such magnifying devices as the jeweler's Loupe
can be used, but do not provide clear details of trichomes.
This is one of the most popular tools for those
who grow cannabis for monitoring trichomes.
Pocket microscopes are some of the
cheapest and simplest microscopes that can provide high magnifications of 100x.
One of the biggest advantages of a pocket microscope is that it can be used out
in the field.
The user can use it in the farm to view and
determine the color of the trichomes. This is particularly due to the fact that
most of these microscopes come with a built-in light that makes it possible for this device to be carried out in to the field for use.
The process simply
involves pointing the microscope at a leaf (or any other part of the plant with
trichomes) and focusing to view and determine the color.
A stereo microscope offers dual magnification. As
such, it is like viewing an object using naked eyes. Using a stereo microscope,
it is possible to observe both the glandular and non-glandular trichomes on the
surface of a plant leaf and stem among other parts.
- Stereo microscope
- Plant leaf or stem
Place the leaf/stem under the stereo microscope.
Increase magnification while focusing and record
Under the stereo microscope, students will be
able to see the fine hairs on the surface of the leaf if the leaf/stem has
non-glandular, hair-like trichomes on its surface. In addition, it's possible
for students to see the heads of capitate glandular hair and secretions (such
as oils) on the cuticle surface from sunken peltate hairs.
The epifluorescence microscope is ideal for
viewing trichomes given that it allows for enhanced specificity and contrast.
This makes it ideal for viewing and differentiating different parts to identify
trichome structures as well as the density of trichomes on any given part of
- epifluorescence microscope
- young leaves/stems
- 4% paraformaldehyde
- phosphate buffered saline
- gel mount
Obtain a young leaf/stem from a young shoot and
fix in 4% paraformaldehyde for about 2 days.
Wash the leaf/stem using phosphate buffered saline
Cut the leaf/stem to obtain a cross-section.
Mount the leaf/stem on a microscope glass slide
and cover with cover slip using gel mount.
Place under the microscope for observation.
* repeat this produce using a young tomato leaf
When viewed under the microscope, the trichomes
are clearly visible as with a bluish background
Related: Microscopy Applications
Check out Leaf Structure under the Microscope
Return to Microscope Experiments
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David G. Hall, El-Desouky Ammar, Kim D.Bowman
and Ed Stover (2017) Epifluorescence and stereomicroscopy of trichomes
associated with resistant and susceptible host plant genotypes of the Asian
citrus psyllid (Hemiptera: Liviidae), vector of citrus greening disease
Rosenthal (2001) The Big Book of Buds: Marijuana Varieties from the World's
Great Seed Breeders.
J. A. Callow, D. L. Hallahan and J. C. Gray
(2000) Plant Trichomes.
Jang-Sean Choi and Eun-Soo Kim (2013) Structural
Features of Glandular and Non-glandular Trichomes in Three Species of Mentha.