Amazing Nature

Trichomes: Nature's Impenetrable Armour

Aug 2023
Author: Green Power
Hong Kong’s native Hairy Nightshade with trichomes and sharp thorns
The Hairy Nightshade, a nightshade plant native to Hong Kong, is covered with trichomes on its leaves, fruits, and branches,along with sharp thorns, which make it difficult for herbivores to consume.
© Vinayaraj @ Wikipedia

Many animals are covered with fur, which they use for insulation, warmth, and courtship displays. Surprisingly, many plants are also covered with hair, known as unique trichome structures evolved from their epidermal cells. While animals can move freely to avoid predators, plants can't. That's why these trichomes become their first line of defence against enemies!

Non-glandular trichomes

Non-glandular trichomes offer physical protection for plants. For instance, Nightshades (Family Solanaceae) typically have leaves covered with spine-like stellate trichomes, making them unusually rough and difficult for herbivores to chew and swallow, increasing the difficulty of feeding. Research has found that a large number of certain species of moth caterpillars are dying from starvation or dehydration due to not being able to feed on the leaves of Nightshades.

The native Hairy Nightshade (Solanum lasiocarpum) not only has trichomes on its leaves but also on its branches and fruits. It even has sharp thorns on its branches, making it challenging for herbivores to swallow.

The hook-like trichomes on the leaves of the Common Bean (Phaseolus vulgaris) have been found to easily puncture insect eggs, effectively preventing them from hatching on the leaves and significantly reducing the chances of these leaves being consumed by the larvae later on. The hook-like trichomes can also harm insects, deterring them from staying or crawling on the leaves. However, some insects have learned to weave silken mats at the tips of the plant's hook-like trichomes, proving that nature always finds a way to overcome challenges!

Common bean with unripe pods
The leaves of Common Bean bear sharp hook-like trichomes, which can harm insects and pierce through insect eggs.
© Rasbak @ Wikipedia

Glandular trichomes

Glandular trichomes, on the other hand, secrete chemical substances. Take Basil (Ocimum basilicum) for example. Its leaves are covered with glandular trichomes that secrete a pungent and intense fragrance of essential oil, causing most insects to steer clear of it. As for humans, they make the most of Basil's aromatic properties and extract its essential oils to create natural mosquito repellents. Additionally, many people adore the unique aroma of basil and often use it as a common herb in cooking.

Common herb Basil
The herbaceous plant Basil, withits glandular trichomes, can secrete a pungent essential oil that effectively repels insects.
© Castielli @ Wikipedia

Some Nightshades have leaves that bear both non-glandular and glandular trichomes. When these plants are under attack, the glandular trichomes secrete a mixture of proteins and metabolites, which can inhibit insect growth. Some components of this mixture even have toxic properties, deterring predators from feeding on them to avoid risking their lives. Studies have also found that plants that have once been attacked develop new leaves with a higher trichome density to enhance their defence capabilities.

Multi-functional trichomes

Trichomes are used for more than just defence in plants. The trapping mechanism of carnivorous plants like the Venus Flytrap (Dionaea muscipula) is actually made up of various unique trichomes. First, the glandular trichomes on the trap secrete nectar to attract prey. When an unsuspecting prey enters the trap, it triggers the sensors inside and causes the trap to close. Finally, the glandular trichomes secrete enzymes to break down and digest the prey, giving full play to the functions of the trichomes.

Carnivorous plants Venus Flytrap with traps
The trichomes on the trap of the Venus Flytrap can attract, capture and digest prey. (Click here to learn more about carnivorous plants)
Photo from Pixabay