Amazing Nature

“Superpower” of Plants

Feb 2022
Author: Green Power
Some mangoes Mangifera indica hanging on tree
Mango (Mangifera indica) releases different volatiles at different stages of maturity as a signal to animals to feed on its fruits, and thus propagate the trees at the most appropriate time.
Photo from Pixabay

Plants are immobile, unlike animals which can move around. Yet, plants are still able to interact with other organisms and the environment. Through a series of biosynthetic processes, simple matter (such as carbon dioxide from the atmosphere) can be converted to complex compounds. Volatiles are then released in different ways to communicate messages with other organisms or their neighbours, in order to tackle environmental stress or even resist attack from others.

Many plants require the help of animals to propagate pollen and seeds for reproduction. Volatile substances are essential. Specialised organs of flowers and fruits, such as epidermal cells and oil glands, are used to store or emit volatiles. The most widely known example is the fragrance released by flowers to attract insects for pollination. Several volatiles are generated by fruits, to inform animals of the different stages of their maturity. This way, the animals know the most suitable time to feed on the fruits, which increases the efficiency of the propagation process.

Calling for help

Apart from reproduction, plants also utilise volatiles for defence. In nature, plants have to face attack from numerous herbivores including insects. When we pick a plant, we often encounter the smell of “grass”. The smell is actually from the green leaf volatiles (GLVs), which are released at the broken part of the plant. GLVs do more than preventing the wounded part from infection; they are also a warning to nearby plants. Their neighbours will enter a “prime state” after receiving the GLVs as a signal to prepare for potential attack. Research has shown that maize seedlings exposed to GLVs can rapidly accumulate compounds such as jasmonic acid as a self-defence mechanism.

Big-eyed Bugs Geocoris species on Wild Tobacco Nicotiana attenuate
Big-eyed Bugs (Geocoris spp.) are attracted to the volatiles released by Wild Tobacco (Nicotiana attenuate), to then prey on Tobacco Hornworm (Manduca sexta).
© Jack Dykinga @ Wikipedia

Amazingly, some plants will “call for help” through volatiles! When Tobacco Hornworm (Manduca sexta) launches a feast on Wild Tobacco (Nicotiana attenuate), the plant emits volatiles that attract the natural enemy of the caterpillars - Big-eyed Bugs (Geocoris spp.), to help them resolve the danger.

Broad-leaved Helleborine Epipactis helleborine
Broad-leaved Helleborine (Epipactis helleborine) releases volatiles that lure wasps to come and pollinate them.
© BerndH @ Wikipedia

Still other plants have evolved more sophisticated survival strategies. Broad-leaved Helleborine (Epipactis helleborine), for example, besides producing nectar, releases volatiles that mimic the presence of wasps' prey, hence luring wasps to come and pollinate them.