Talking Plants

01/09/2009

Talking Plants

Maneka Gandhi

(Bihar Times) I shudder when I see cut flowers or anyone idly plucking leaves. We don’t mow the grass in my house and it behaves beautifully. For me, people who keep bonsais are the equivalent of butchers. When you understand that a plant is a stationary but equally sensitive being, you’ll probably stop ill treating it too.

After ten years of studying all the experiments on plants, Australian scientists have established that plants have human-like attributes. Venus Fly Traps and Mimosa plants can move, pitcher plants eat animals while peaches and cherries calculate the number of cold days each year before sprouting leaves in the spring. They even talk to each other and call in reinforcements when the going gets tough.

In fact, the landscape around us is filled with chatter. Plants exchange information with each other, and with insect pollinators, seed dispersers, herbivores and enemies of those herbivores. Biologists use chemical sensors, to decode these odour molecules denoting cries for help, invitations, warnings et al that float past human noses unnoticed. They have discovered that plants use chemical cues to repel predators and attract allies i.e those insects that feed on the insects that feed on the plant. They have also found that neighbouring plants pick up these conversations and gear up their own defenses.

A must read book, The Secret Life of Plants, had earlier introduced the idea of humans talking to philodendrons. Now we learn that the philodendrons talk back. Researchers have documented maple, willow, poplar, alder and birch trees listening to their own kind. Even barley seedlings listen to other barley seedlings. Plants like strawberry, clover, reed and ground elder form internal communication networks for efficient information exchange with individual plants connected by means of runners in a manner similar to computer networks.
So what do plants talk about?
One study found that clover plants use these network lines to warn each other when an enemy approaches. For example, a plant attacked by caterpillars will alert all other members of the network. These will then activate their protective mechanisms and trigger chemical and structural changes to render their leaves less tasty and harder to bite. Even unrelated plants pick up chemical alarms. For example, cucumbers respond to the signals of injured lima beans.

Dutch scientists offer evidence that plants under attack enlist the help of their enemy’s enemy. When spider mites attack lima bean plants, the plants release a chemical SOS that summons the mite that preys on the spider mite.. Similarly, when caterpillars descend on corn, tobacco, and cotton, the beleaguered plants release chemicals to attract parasitic wasps. So specific are these signals that they attract only those wasps that lay their eggs on the type of caterpillar infesting the plant. "Plants don’t just say, 'I am damaged,' they also specify who is damaging them," avers Professor Consuelo De Moraes of Pennsylvania State University. Distress signals from mite-infested cotton and lima beans prompt undamaged plants to send out pre-emptive calls to enemies of the infesting mite. Today scientists agree that plants talking to bodyguards is a characteristic of most, if not all, plant species .
Plants time their signals to reach their intended audience. Parasitic wasps hunt during the day so that's when infested plants will release an SOS directed at them. At night, tobacco plants release a chemical concoction that discourages nocturnal moths from laying eggs that produce tobacco-devouring caterpillars.

Because they require especially strong survival skills, tobacco plants are a favourite subject of study. Their seeds can lie dormant for a century so once they start growing , they may face unfamiliar enemies. Moreover, after germination, they have only one season to flower and reproduce. So the plant has to optimize growth, and repel predators whilst creating seeds. Successful seedlings must fend off the caterpillars of hawkmoths, leaf bugs, flea beetles, and mirids. One study placed a hungry caterpillar on several plants. It found that when a caterpillar bites into a leaf, the plant identifies the insect's saliva and initiates a chemical defense. Some plants produce toxins like nicotine to kill the insect , others produce compounds that slow down or arrest the invader's ability to digest the plant. Should these fail, the plant releases airborne chemical repellants. If still, an insect like the hawkmoth settles down on it to lay eggs, the plant summons Geocoris pallens, a small, fast, and rapacious predator of hawkmoth eggs. Through chemical emissions, a plant can reduce insect attack by upto 90 %!

Kyoto University researchers found an additional warning that endangered plants emit. They specifically alert relatives and clones (genetically identical cuttings) growing nearby, proving that plants recognize kin. A sagebrush plant can recognize a genetically identical cutting close by, and the two clones communicate and cooperate to avoid being targeted by herbivores. Researchers speculate that plants identify themselves through their roots using tiny chemical signatures specific to each family. Root systems grow differently depending on whether they bump into themselves or a neighbour’s and whether that neighbor belongs to a local or distant community. Flowers of many species can tell their own pollen from that of another.

Family feeling in plants was first demonstrated by a Canadian study. When plants of the same species but strangers are potted together, each extends its root growth to monopolize soil and water. But siblings from the same mother plant allow each other ample root space, and planted together grow taller and stronger.

Plants calculate the length of days, using that information to decide when to flower. Daffodils bloom in spring as the days get longer. Roses wait until summer. Rice flowers choose autumn as the days shorten. Years ago, Russian scientists speculated about a substance being transported from the leaves to shoot tips, stimulating the formation of flower buds. They named this mystery chemical "florigen." Now research reveals that a gene called FT, whose activity is regulated by day length, produces a messenger molecule that is sent to the shoot tip to talk to proteins that exist at the future locations of buds so that flowers are born at just the right time.

Under stress, plants react just like humans, seeking relief from an aspirin-like mix of chemicals which they produce. Colorado scientists have found methyl salicylate, the chemical form of aspirin is emitted into the atmosphere as plants respond to drought, unseasonable temperatures and other stresses. Methyl salicylate has two functions. One is to build up the plant’s own immunity levels to resist and recover from disease. The second is to communicate the threat to neighboring plants. The methyl salicylate that accumulates in the atmosphere above a stressed forest activates the immune responses of plants even faraway.