Toronto Star column – published January 12, 2013
Everyone has heard of the ‘horse whisperer’, a story about a man named Tom Booker who could communicate with horses on an extraordinary level: almost paranormal. Daniel Chamovitz is the plant whisperer.
Mr. Chamovitz is the director of the Manna Centre for Plant Biosciences at TelAvivUniversity where he has been studying plant behaviour for many years. An accumulation of his considerable knowledge on the subject of how plants communicate is found in his recently published book, “What a Plant Knows. A field guide to the senses.”
It makes for fascinating reading for anyone that has spent any time around plants. Which would be most of us.
In the first four chapters Chamovitz breaks the book down into the four senses, as humans understand them: sight, smell, what a plant feels, and what it hears. He concludes with ‘how a plant knows where it is’, ‘what a plant remembers’ and finally ‘the aware plant’. All of it is revealing in the extreme. Here is my summary of the content:
The idea that plants communicate is not a new one. According to the author, Charles Darwin performed many experiments on plants in an effort to understand them better. As far back as the 1850’s Darwin was busy asking questions and experimenting with plants in an effort to understand them. He was good at it: Mr.Chamovitz and, by extension, you and I are the beneficiaries of Darwin’s work and that of many scientists after him.
What a plant sees.
While plants do not have eyes as we think of them, they do possess the ability to sense light. The question is ‘how?’ and ‘why?’ Through a process called phototropism, a seedling ‘sees’ light through the tip of its young growth. When light hits the tip of the shoot it bends in that direction. This explains why you need to turn your amaryllis bulb every couple of days away from natural light in order to keep it growing straight.
Many plants flower in response to light. More accurately, they flower in response to short days. A poinsettia produces vividly coloured bracts on its upper leaves in response to short days, thus providing us with a flowering plant around Christmas time, which is only 4 days after the shortest day of the year. The same can be said for Christmas cactus and, for that matter, Easter cactus, the latter reacting to short days more slowly.
It is interesting to note that an apple tree is similarly conditioned by short days to flower in April. But why doesn’t it also flower in September when we experience equally short days? The answer is that the apple tree, much like other spring flowering plants also requires a period of cold in order to trigger blossoms. A plant can be fooled into thinking that September is a good time to bloom, especially after a cool or wet August, which explains why magnolias are frequently found in flower in early fall.
What a plant smells.
I rubbed my fingers on the leaves of a mint plant and held them out to my nephew, “Here, smell my finger!” I exclaimed. He recoiled as if he had heard this before. Poor kid, no sense of humour. Maybe no sense of smell.
Plants do not have noses but they do have the ability to sense an odour given off by plants nearby. If you put an apple in a brown paper bag with an under ripe avocado, the avocado will ripen very quickly. Experiments undertaken in the 1930’s by Richard Gane in Cambridge point to the answer: ethylene. This is the universal plant hormone responsible for fruit ripening. An apple gives off this gas around its immediate vicinity, which is sensed by neighbouring fruit as a signal to get on with the business of ripening.
Trees are now known to communicate with one another through scent, especially when danger is present. David Rhoades and Gordon Orians, scientists from the University of Washington, noticed that caterpillars were less likely to forage on leaves from willow trees if these trees neighboured other willows already infested with tent caterpillars. The healthy trees neighbouring the infested trees were resistant to the caterpillars as the leaves of the resistant trees contained phenolic and tannic chemicals that made them unpalatable to the insects.
Rhoades proposed that the attacked trees must be sending an airborne ‘alarm’, a pheromone message, to the healthy trees. The suggestion is that the neighbouring plant must be practicing a form of olfactory eavesdropping on an internal signal actually intended for other leaves on the same plant.
Can we talk?
Chamovitz asks the earth shattering question, “When a plant releases a smell in the air, is it a form of talking or is it just passing gas?” This and other pressing questions are not necessarily answered in the book, but they do get you thinking.
In this chapter on smell, the theory is advanced that plants can not only send scented messages to one another but also that different plant parts communicate with other plant parts on the same plant. A tomato plant, for instance, will know when you walk past it as you brush up against its foliage. Once the leaves have been so informed they emit a smell that is picked up by foliage on other parts of the same plant. Natural defences are sent up to the opposite side of the tomato plant as a result.
Beetles that eat leaves on a plant produce the same results. Sometimes the flowers on the same plant, while not directly affected by the biting insect, will produce a type of nectar that attracts beetle-eating arthropods. I can hear the bugle call of the arriving cavalry now!
To a degree this book offers up evidence that plants communicate based on ancient knowledge of them. As long as there has been a perfume or ‘fragrance’ industry, we have played with plants’ ability to produce specific scents. For the most part, it is the human response to plant scent that interests Oscar de la Renta or whoever. Chamovitz is interested in how the same scents that affect people also affect plants. He uses a technique called ‘mass spectrometry’, a process often featured on the TV show CSI and employed by perfume companies when developing new fragrances.
A plant is much smarter than we generally give it credit for. Scientific experiments have proven that when attacked by a disease a lima bean plant emits methyl salicylate and when eaten by bugs the same plant produces a gas called methyl jasmonate. Why two different responses? Because a unique response is required to heal the plant depending on what precisely is attacking it.
Next week, more proof that your plants are more than just a pretty face: how they feel, hear, and what a plant remembers. Fascinating stuff, thus an article in two parts.
What A Plant Knows
By Daniel Chamovitz