Science Talkies -What plants talk about

This documentary was screened as a part of the “Science Talkies” initiative in our Education Resource Centres. The following article is a briefing of the content of the documentary.

Have we ever wondered how it would be if plants could talk?

Can we tell if they are happy or disappointed?

Can  plants think?

Plants do not have eyes or ears, but, they can find their food. They lack a brain, but some scientists think that they can communicate, cooperate and even wage war. The plants do not live a solitary life. They live as a community just like any other organism. They actively respond to the availability of nutrients, predators, herbivory and various other biotic and abiotic stress.

Can  plants move?

Do plants behave like animals? What might be the advantage animals have over plants? Is it locomotion? Plants might not hop or jump or walk, but they do move. The movement is significantly slow mostly and every movement is in response to something. For example, growth. Can all the movement of plants be compared to that of animals? Taking the example of an animal moving towards its food, can plants do anything of that sort?

Yes, they can.

1. Generally, the plants grow in response to sunlight.
2. The carnivorous plants like Venus fly trap have brightly coloured leaves with sensory hairs that can close within seconds and trap the insects that sit on them. It is then digested to avail the nutrient need of the plant.
3. The root’s behaviour in search of water and nutrients is just like any animal searching for its food. Scientists had set up a camera under the soil and had taken pictures to find how the movement of roots took place. If the root sensed the availability of nutrients, it grows faster in three days to reach it and then slows down until necessary nutrients are absorbed.

Can  plants communicate?

How do plants manage to get what it want? Parasitic plants like Cuscuta sense the chemicals produced by other plants to find its host. In a series of experiments, scientists placed  wheat and a tomato plants in the same pot. When a daughter vine of Cuscuta was kept in the pot, it chose tomato plants as host. Similarly, when the chemical component from the tomato plant was kept alongside a covered tomato plant, the Cuscuta vine showed movement towards the chemical component.   

When plants are being eaten by insects or caterpillar, their parts are being cut and certain chemicals are produced. These chemicals become signals that  invite  other set of insects called natural predators of the grazing insects. Can this be an accident? Or is it an example of co-evolution.

An example of this type can be wild tobacco that generally grows in the forests. This plant is capable of switching its flowering time in just 8 days.

The flowers of wild tobacco bloom at  dawn and it is the perfect timing for the hawk moth. The moth sucks in the nectar, but, unknowingly carries pollen and establishes pollination. The moths lay eggs while visiting flowers. These hatch into caterpillars. The plants have stored nicotine for defence but these little crawlers are resistant to nicotine. As the caterpillars invade the plant, the plant produces volatile compounds and calls for help. These calls are answered by bugs called Geocoris which feed on the caterpillar. But yet, the hawkmoth manages to lay 200 eggs at once. The plant would not give up. Under such threats, the plant switches its flowering time to the day light. The flower now has a different colour, volume of nectar and high concentration of sugar and is pollinated by the humming bird.

Can plants withstand fire?

Yes, there are plants that can withstand fire.. Some plants have evolved to survive in habitats where wild fires are common. They have adapted by producing a resin coat around the seeds to protect them from forest fire. In fact, the fire removes the resin covering on these seeds preparing them for germination.

Fire also burns most other plants producing a lot of ash, rich in nutrients necessary for plants. Thus, increasing the nutrient supply, which kick starts the germination.

Plants can cooperate and rage war!

How does a plant account for its social life? Is there sharing of resources among them or fights? It so appears that, sometimes, they can live in harmony whereas with some specific plants called weeds, the competition and fights are ensured. Spotted Knapweed from Europe is one  such weed with not just brightly coloured attractive flowers, but also war raging capabilities for the territory under ground. These weeds produce certain chemicals in the soil, that makes the soil unfit for other plants to survive. These weeds are insect pollinated. However, the Wild Lupines can lodge counter attack and control Knapweeds.

Some coastal plants can identify other closely related plants via the chemical signal produced in the roots. But, the most fascinating question is, how could have the oldest trees in the tropical rain forests survive? Have they been fighting for resources like nutrients and water under soil? Have they been fighting territorial war with neighbouring trees? Looks like they have some group mediator organisms to maintain harmony.

The mushrooms that pop out during rain, led a group of scientists to find out that, the fungal body called mycelia under soil are thread like and long. These threads run, interconnecting trees from neighbourhood to a farther distance. Mere chemical signals in these mycelia can bring in an advantage to the tree especially in the process of absorption. So the trees are all actually connected underground by roots and also fungi. The relationship between trees and fungi are symbiotic as the fungi depend on trees for the carbon rich sugar and the fungi help in providing nutrients for trees. Cotton wood trees are known to have such symbiotic association with a fungus named Coenococcum. Plants like grass and orchids also have such fungal root partners.

Don’t all these make plants living marvels? The mother trees can nurture their own kind. Plants can recognise  their family members and communicate with their friends and foes. They have no way to organise or integrate the information they receive due to the lack of a brain. Yet, are efficient in showing movements precisely using chemical signals like growth or the periodic blooming of flowers. All these  aspects of plants make them interesting to learn about them. After all, they are not that boring at all.