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Plant Trichomes
Trichomes have many different features that vary between both species of plants and organs of a singular plant. These features affect the subcategories that trichomes are placed into. Some defining features include:


 * Straight (upright with little to no branching), Spiral (corkscrew-shaped) or Hooked (curved apex)
 * Presence of cytoplasm
 * Glandular (secretory) vs. Eglandular
 * Tortuous, Simple (unbranched and unicellular), Peltate (scale-like), Stellate (star-shaped)
 * Adaxial vs. Abaxial determines whether trichomes are present, respectively, on the upper surface or inner surface of the plant

In a model organism, C. salvifolius, there are more abaxial trichomes present on this plant because this surface suffers from more UV, solar irradiance light stress than the adaxial surface.

Trichomes can protect the plant from a large range of detriments, such as UV light, insects, transpiration, and freeze intolerance.

Trichome Development
Many of what scientists know about trichome development comes from the model organism Arabidopsis thaliana, because their trichomes are simple, unicellular, and non-glandular. The development pathway is regulated by three transcription factors: R2R3 MYB, basic helix-loop-helix, and WD40 repeat. The three groups of TFs form a trimer complex (MBW) and activate expression of products downstream, which activates trichome formation. However, just MYBs alone act as an inhibitor by forming a negative complex.

Phytohormones
Plant phytohormones have an effect on the growth and response of plants to environmental stimuli. Some of these phytohormones are involved in trichome formation, which include gibberellic acid (GA), cytokinins (CK), and jasmonic acids (JA).

GA stimulates growth of trichomes by stimulating GLABROUS1 (GL1).

However, both SPINDLY and DELLA proteins repress the effects of GA, so less of these proteins create more trichomes.

Some other phytohormones that promote growth of trichomes include brassinosteroids, ethylene, and salicylic acid. This was understood by conducting experiments with mutants that has little to no amounts of each of these substances. In every case, there was less trichome formation on both plant surfaces, as well as incorrect formation of the trichomes present.

Glandular Trichomes
Glandular trichomes have been vastly studied, even though they are only found on about 30% of plants. Their function is to secrete metabolites for the plant. Some of these metabolites include:


 * terpenoids, which have many functions in the plant related to growth and development
 * phenylpropanoids, which have a role in many plant pathways, such as secondary metabolites, stress response, and act as the mediators of plant interactions in the environment
 * flavonoids
 * methyl ketones
 * acyl sugars

Non-glandular Trichomes
Non-glandular trichomes are important for plant protection against UV light.

The model plant, Cistus salvifolius, is found in areas of high-light stress and poor soil conditions, along the Mediterranean coasts.

It contains non-glandular, stellate and dendritic trichomes that have the ability to synthesize and store polyphenols that both affect absorbance of radiation and plant desiccation. These trichomes also contains acetylated, which can absorb UV-B and non-acetylated flavonoids, which absorb the longer wavelength of UV-A.

Polyphenols
Non-glandular trichomes in the genus Cistus were found to contain presences of ellagitannins, glycosides, and kaempferol derivatives.

The ellagitannins serve a main purpose of adapting in times of nutrient-limiting stress.

Flavonoids
In non-glandular trichomes, the only role of flavonoids is to block out the shortest wavelengths to protect the plant, which differs from glandular trichomes.

Research performed
Researchers were able to autofluoresce trichomes in this model organism to find where the biomolecules were located and how they changed as they were hit with light.

The chemical components of both adaxial and abaxial trichomes were determined using fluorescence techniques. The arms of the trichomes fluoresce in yellow when excited with green-blue light and stained with NR. However, when trichomes were unstained and excited at 365 nm, they fluoresce in the red orange region.

This data agrees with previous evidence which determines that these trichomes consist of flavonoids.

Arabidopsis thaliana trichome classification
Arabidopsis thaliana trichomes are classified as being aerial, epidermal, unicellular, tubular structures.