A “head” of Romaine lettuce/Wikimedia Commons

An international team of scientists has discovered that plants have feelings, too.

When insects nibble on the leaf of a rockcress plant, the group led by Masatsugu Toyot of Japan’s Saitama University reported, the injured leaf signals other leaves to warn them of what is happening.

Like animals, the scientists wrote in a paper published in Science on Friday, the plants use glutamate to transmit their feelings.

An amino acid, glutamate has been identified as the major neuro-transmitter in animals. Toyot and colleagues from the University of Wisconsin Madison, the University of Missouri Columbia and Michigan State University East Lansing , have now linked glutamate to a similar function in plants.

“This glutamate-based long-distance signaling is rapid: Within minutes, an undamaged leaf can respond to the fate of a distant leaf,” they wrote.

At the Neurohacker Collective, Lauren Alexander explains glutamate’s function this way:

“Glutamate is the most abundant neurotransmitter in our brain and central nervous system. It is involved in virtually every major excitatory brain function. While excitatory has a very specific meaning in neuroscience, in general terms, an excitatory neurotransmitter increases the likelihood that the neuron it acts upon will have an action potential (also called a nerve impulse). When an action potential occurs the nerve is said to fire, with fire, in this case, being somewhat akin to the completion of an electric circuit that occurs when a light switch is turned on. The result of neurons firing is that a message can be spread throughout the neural circuit. It is estimated that well over half of all synapses in the brain release glutamate, making it the dominant neurotransmitter used for neural circuit communication.”

Pain?

People for the Ethical Treatment of Animals (PETA) and other animal-rights activists used these neural firings to argue that fish feel pain.

“Fish don’t audibly scream when they’re impaled on hooks or grimace when the hooks are ripped from their mouths, but their behavior offers evidence of their suffering—if we’re willing to look,” PETA claims on its website. “For example, when (scientist Victoria) Braithwaite and her colleagues exposed fish to irritating chemicals, the animals behaved as any of us might: They lost their appetite, their gills beat faster, and they rubbed the affected areas against the side of the tank.”

A reaction to a stimulus is not, however, proof of pain. All that can be determined for certain is that the fish are, like the plants studied by Toyot and others, responding to changes in their environment as do all species trying to survive.

The question of whether it’s OK to eat fish has for years been a hot one for non-meat-eating humans concerned that they might be causing other species pain.

“The lentils and nut cutlets are starting to fly in a food fight that has pitted vegetarians against those who shun meat but eat fish,” Emily Dugan wrote in The Independent, a London publication, almost a decade ago.

“The row follows a report about the problems of finding good vegetarian food in restaurants, which prompted a report in The Independent by our consumer affairs correspondent, who does not eat meat but who does eat fish.

“Purist vegetarians have hit back at that article and, in doing so, have rekindled a dispute within non meat-eating circles. The difference, argue the fundamentalist veggies, is clear: eat fish and you cannot be considered a genuine member of the community.

“Our finned friends feel pain, they say. Dine on them and your outlook on the animal world is distinctly different to those who stick with mung beans and Quorn.”

Since Dugan wrote that story, the debate has only deepened.

Fish like plants?

An international team of neurobiologists, behavioural ecologists and fishery scientists in 2013 concluded that while fish have feelings, there is no reason to believe it rises to the level of pain.

They concluded, as reported by Science Daily, that “fish do not have the neuro-physiological capacity for a conscious awareness of pain. In addition, behavioural reactions by fish to seemingly painful impulses were evaluated according to human criteria and were thus misinterpreted. There is still no final proof that fish can feel pain.”

The scientists noted that fish, like plants, lack a neocortex, where pain is processed in humans, and recognized the problem of reaching conclusions as to “underlying emotional states based on behavioural responses,” Science Daily reported.

“Moreover, fish often show only minor or no reactions at all to interventions which would be extremely painful to us and to other mammals. Pain killers such as morphine that are effective for humans were either ineffective in fish or were only effective in astronomically high doses that, for small mammals, would have meant immediate death from shock. These findings suggest that fish either have absolutely no awareness of pain in human terms or they react completely different to pain. By and large, it is absolutely not advisable to interpret the behaviour of fish from a human perspective.”

The study was being done at a time when amendments to the German animal protection law were under consideration. Germany has the most protective animal welfare standards in the world.  Animal rights activists there have tried to end recreational fishing as cruel.

They have succeeded in eliminating targeted catch-and-release fisheries, but catch-and-release continues in fisheries where size limits on fish are imposed. A group of German researchers in 2014 concluded “that convincingly answering the question of whether or not fish feel pain is unlikely to alter the social climate related to recreational fishing.”

PETA Germany is now protesting the violent video game “Far Cry 5,” which features the killing of a lot of people, because of its “gamification” of fishing.

“Fishing means luring fish into a trap, exposing them to fear and shortness of breath for minutes to hours, as well as to an agonizing death struggle before being killed or often cut alive,” Newsweek quoted a PETA spokeswoman saying. “Today we know that a fish is somebody, not something, and it is an indictment to promote fishing. Fish are curious vertebrates with individual personalities.”

What PETA will make of the feelings of plants remains to be seen.