Edythe Falconer - Ottawa
Book Review “What Plants Know” by Daniel Chamovitz
If “intelligence” is a biological property how does it work in plants? Current research is subjected testy dialogues over interpretations where disagreement rests not as much on results as it does on interpreting them. Having read “What Plants Know” I wonder if I’ve been taking plants for granted - not appreciating them enough for the wondrous creations they are.
Chapter 1Plants “see” blue, red and far red as received by protein photoreceptors in a process called phototropism. Plant “sight” helps to regulate various plant responses. The Maryland Mammoth tobacco plant revolutionized the tobacco industry when growers discovered it would bloom earlier if they controlled the amount of light it received via a process called photoperiodism. This phenomenon continues to be useful commercially.
Chapter 2Plants emit odors both pleasant and unpleasant. In nature these volatile chemical exchanges can function as plant Morse code for signalling impending danger. Plants can then change their chemical composition to make it less appealing and even toxic to predators. The parasitic dodder provides an interesting example of plant taste. Given a choice between wheat or tomato it always chooses tomato.
Chapter 3Plants sense being touched. Humans have neuron mechanoreceptors powered by electrical signalling. Venus flytrap is a good example of a plant that senses and reacts to the touch of potential prey. The lobes of its flower are edged with cilia that respond to pressure from insect visitors. If electrical stimulus on hairs inside the lobes is sufficient the trap closes. Two need to be touched within 20 seconds.
Chapter 4Research thus far doesn’t indicate that plants can “hear”. Human ears have hair cells that respond to sound while plant roots have root hairs that are sensitive to nutrition and moisture. Both capacities aid species survival. Most fascinating - both humans and plants possess deaf genes. Gene mutations may cause shorter root hairs and consequent reduction in root hair function. In humans these mutated genes cause deafness.
Chapter 5Try to make a plant grow upside down and you soon discover plants know up from down. This is proprioception in a form called gravitropism. The upper part of the plant defies gravity while roots respond positively to it. Plants dance in circles. Darwin was correct when he asserted that circumnutation is a built-in behavior of plants. Plant statoliths in the centre of the root cap are similar to otoliths in our inner ear.
Chapter 6Human memory is procedural, semantic and episodic memory. Plants demonstrate procedural memory. Venus flytrap possesses a 20 second memory. Plant memory is also indicated in Dosta’s study of morphogenetic memory in plants and Lysenko’s work with winter wheat beginning in 1928. Epigenetics research studies changes in gene activity that can pass from parent to offspring - season to season and generation to generation. Memory in plants is achieved by cell-to-cell signaling similar to that in human neurons communication.
EpilogueAnthony Trewavas of University of Edinburgh comments “It is unlikely that intelligence as a biological property originated only in Homo sapiens.” Michael Pollan, in his essay “The Intelligent Plant”, reminds us that “Plants dominate every terrestrial environment, composing 99% of biomass on earth. By comparison, humans and all other animals are, in the words of one plant neurobiologist, “just traces.”
Reviewer Note: “What Plants Know” is fascinating. If you haven’t already read it – read it. If you have read it – read it again! It’s even better the second time around. EF