UB Researchers Find That Plants' "Memory" Hastens Production of Chemical Toxic to Pests

ATLANTA -- Forewarned is forearmed and, according to University at Buffalo biologists, plants are no exception to that survival rule.

Plants "remember" when they've been attacked and they respond faster to future attacks by hastening production of chemical defenses, Ian Baldwin, Ph.D., UB associate professor of biological sciences reported today at the annual meeting of the American Association for the Advancement of Science.

Baldwin said the research, which eventually will be useful in developing generations of pest-resistant plants, demonstrates that plants have a more sophisticated relationship to their environments than is commonly thought.

"We have this idea that animals are smart, and that they have knowledge of their environments and of predators, but we don't at all have that perception of plants," he added.

"This research is helping us develop that perception, that plants are individuals with histories, who perceive their environments and who have evolved responses to those environments," he said.

Baldwin spoke at a session focusing on the pathways through which animals and plants perceive injury or damage, and how they respond.

The UB research supports the premise that plants defend themselves using a chemical pathway, called a signal-transduction pathway, that parallels the one involved when animals register damage or injury internally and respond to it.

"Animals can run away, plants cannot," said Baldwin. "But both plants and animals use a similar signal-transduction pathway to say 'you're damaged.'"

While animals respond to damage by producing prostaglandins and experiencing pain, plants respond by inducing the production of chemical defenses, Baldwin said.

To determine whether or not memory is at work in plants' defenses, Baldwin and his colleagues needed to uncouple the wounding from the response to the wounding.

"A key issue for unraveling the signal cascade involved in these chemical defenses was to elicit the response to the wound without actually wounding the plant," said Baldwin.

If the experiments had involved actually damaging the leaves, plants would have had to be repeatedly wounded, generating significant scar tissue and possibly resulting in a plant with no leaves.

"We needed to isolate the cue that causes the plant to produce alkaloids (toxic chemicals plants produce defensively), so that we could ask these questions in a much more rigorous way that isn't confounded by the secondary aspects of wounding," Baldwin explained.

The UB researchers, the first to explore memory in whole plants, studied a native species of tobacco, Nicotiana sylvestris. Damage to its leaves activates production of jasmonic acid, which, in turn, activates production of nicotine, which is toxic to pests.

To induce a defensive response, the researchers added jasmonic acid at different intervals to the roots of plants grown in solution.

Plants were dosed with the same amount of jasmonic acid once, twice or three times during an 18-day period, allowing six days between inductions so that the defensive response could subside.

According to Baldwin, plants that had two prior inductions attained significant increases in their nicotine pools two days earlier than did plants with one or no prior inductions.

"Our work shows that plants make their nicotine faster if they've had prior exposure to the signal," said Baldwin.

Baldwin describes the memory mechanism in plants as a type of "immunological memory."

"The reason why vaccines work in humans and animals is that you're stimulating the immune system to remember something. In the same way, it seems that plants do have memories from prior attacks," he said.