Plants Interacting

From the New York Times

The sea rocket, researchers report, can distinguish between plants that are related to it and those that are not. And not only does this plant recognize its kin, but it also gives them preferential treatment.

If the sea rocket detects unrelated plants growing in the ground with it, the plant aggressively sprouts nutrient-grabbing roots. But if it detects family, it politely restrains itself.

The finding is a surprise, even a bit of a shock, in part because most animals have not even been shown to have the ability to recognize relatives, despite the huge advantages in doing so.

If an individual can identify kin, it can help them, an evolutionarily sensible act because relatives share some genes. The same discriminating organism could likewise ramp up nasty behavior against unrelated individuals with which it is most sensible to be in claws- or perhaps thorns-bared competition.

“I’m just amazed at what we’ve found,” said Susan A. Dudley, an evolutionary plant ecologist at McMaster University in Hamilton, Ontario, who carried out the study with a graduate student, Amanda L. File.

“Plants,” Dr. Dudley said, “have a secret social life.”

Since the research on sea rockets was published in August in Biology Letters, a journal of the United Kingdom’s national academy of science, Dr. Dudley and colleagues have found evidence that three other plant species can also recognize relatives.

The studies are part of an emerging picture of life among plants, one in which these organisms, long viewed as so much immobile, passive greenery, can be seen to sense all sorts of things about the plants around them and use that information to interact with them.

Plants’ social life may have remained mysterious for so long because, as researchers have seen in studies of species like sagebrush, strawberries and thornapples, the ways plants sense can be quite different from the ways in which animals do.

Some plants, for example, have been shown to sense potentially competing neighboring plants by subtle changes in light. That is because plants absorb and reflect particular wavelengths of sunlight, creating signature shifts that other plants can detect.

Scientists also find plants exhibiting ways to gather information on other plants from chemicals released into the soil and air. A parasitic weed, dodder, has been found to be particularly keen at sensing such chemicals.

Dodder is unable to grow its own roots or make its own sugars using photosynthesis, the process used by nearly all other plants. As a result, scientists knew that after sprouting from seed, the plant would fairly quickly need to begin growing on and into another plant to extract the nutrients needed to survive.

But even the scientists studying the plant were surprised at the speed and precision with which a dodder seedling could sense and hunt its victim. In time-lapse movies, scientists saw dodder sprouts moving in a circular fashion, in what they discovered was a sampling of the airborne chemicals released by nearby plants, a bit like a dog sniffing the air around a dinner buffet.

Then, using just the hint of the smells and without having touched another plant, the dodder grew toward its preferred victim. That is, the dodder reliably sensed and attacked the species of plant, from among the choices nearby, on which it would grow best...

Although a view of plants as sensing organisms is beginning to emerge, scientists have been finding hints of such capabilities and interactions for 20 years. But discoveries have continued to surprise scientists, because of what some describe as an entrenched disbelief that plants, without benefit of eyes, ears, nose, mouth or brain, can and do all they are seen to do...

At the extreme of the equality movement, but still within mainstream science, are the members of the Society of Plant Neurobiology, a new group whose Web site describes it as broadly concerned with plant sensing.

The very name of the society is enough to upset many biologists. Neurobiology is the study of nervous systems — nerves, synapses and brains — that are known just in animals. That fact, for most scientists, makes the notion of plant neurobiology a combination of impossible, misleading and infuriating....

“Plants do send electrical signals from one part of the plant to another,” said Dr. Eric D. Brenner, a botanist at the New York Botanical Garden and a member of the Society of Plant Neurobiology.

Although those signals have been known for 100 years, scientists have no idea what plants do with them.