The Talking Planet
What’s the flower telling the butterfly?
While scientists continue to explore the idea of plants “talking” to other plants, they know that plants do “talk” to insects. Plants produce chemical signals that contain important messages.
A smell is a message. Flowers attract insects with fragrances that say, “Here’s food for you.” Butterflies are attracted to flowers that smell sweet. Beetles are attracted to flowers with spicy scents. A bad taste is another message. Some flowers contain a poison called pyrethrum
(pi re ‘threm). Its message is blunt: “Bug off!” An insect gets the message after its first taste.
Signals in the Soil
Insects aren’t the only organisms that get messages from plants. Tiny bacteria in the soil receive messages from plants called legumes (leg’yums). And the bacteria actually “talk” back!
Legumes are plants such as soybeans, peas, and alfalfa. These plants can change nitrogen gas in the air to forms of nitrogen that plants need for growth. Well, the legumes don’t exactly do this on their own. The plants provide homes and food for bacteria called Rhizobium
(ri zo’bi um). But the bacteria do the work.
As the pictures show, the legumes construct little bumps called nodules on their roots. The nodules become a home and factory for the bacteria. The bacteria live inside the nodules and feed on sugars made by the plant. In return, the bacteria make the nitrogen compounds that the plants need for growth. So, as you can see, both the plants and the bacteria benefit from this partnership.
How do legumes and Rhizobium get together? Molecular biologist
Sharon Long discovered that alfalfa plants and Rhizobium “talk” to one another. Alfalfa starts the “conversation” by sending out a chemical called a flavonoid chemical puts out a call to all Rhizobium in the soil: “Come to work in exchange for room and board.”
When the Rhizobium receive the message, they send their own chemical reply. They release a chemical into the soil that carries this message to the alfalfa plant: “We’ll be there soon. Start making our nodule homes.” Long and her co-workers think the conversation continues. They are doing experiments to find out what the alfalfa says next.
(Each antenna of the male silkworm moth may have 70 branches. Each branch has thousands of hairs that detect tiny amounts of female sex pheromones.)
Talking Long Distance
As you learned, a hormone works within a living thing, where it carries messages to certain parts of the organism. A pheromones is a chemical that communicates information between two or more members of the same species. You might say that pheromones are long-distance hormones.
Pheromones are especially important in insect communication. Some insects, like butterflies, live by themselves. Others-like ants, aphids, and honey bees-live in large, crowded communities.
Without pheromones two tiny insects might never find each other in the thick grass. In many species, a female releases a sex pheromones that causes a male of her species to stop in his tracks. He picks up the signal with long, feathery antennae like those in the picture. The antennae can detect very tiny amounts of the female pheromone a male detects the scent, he will follow the fragrant pheromone path directly to the female. The male might then release his own pheromones to let the female know that she is about to be “courted.”
Why are sex pheromones important? Well, the answer isn’t exactly romance, as the cartoon suggests. Sex pheromones are necessary for the survival of a species. They help males and females of the same species find each other so that they can reproduce.
Pheromones work just as well for insects that live in large groups. Pheromones broadcast information quickly, which can be very important when danger threatens. When a honeybee stings an enemy, the bee releases a pheromone that smells like bananas. The pheromone travels quickly through the air, sending an alarm message to other honeybees. When the other bees smell this alarm pheromones they’re attracted to it. They quickly gather and get ready to help defend the hive.
