What Do Plants Know?
by Jack Kittredge
A recent MIT study showing that rice seeds can ‘hear’ the pitter-patter of raindrops, and sprout up to 40% faster than they would otherwise, got me curious. The authors asserted that natural environmental sounds stimulating growth in seeds had not been previously demonstrated. I wondered if studies had been done demonstrating any kinds of “sensing” by plants of environmental forces. Obviously they grow towards sunlight, but how about more subtle effects?
When I was young I remember groups claiming that plants (particularly weed, as I recall) flourished when in the presence of music. The groups were selling recordings claimed to generate this effect, called things like PlantWave, Sonic Bloom, and Plantasia. But there was no real science cited to back them up. Since then, however, papers have been published with more credibility. A 2014 study in Oecologia showed that cress can detect the sounds of caterpillar chewing (as opposed to wind vibrations), and produced an increased amount of chemical toxins to repel the caterpillars in response. Similar sensitivity has been shown for “buzz pollination” occurring when the sound of bees buzzing stimulates a significant pollen release by a plant.
How about sight? Work on this is more limited, but a 2014 report in Current Biology reveals that the climbing wood vine can camouflage itself by modifying its leaves to mimic the color and shape of its host plant. How does it know its color and shape, though? European plant biologist František Baluška discusses in Trends in Plant Science the discovery of a cyanobacterium that uses its entire cell body to focus light on its cell membrane. Such a simple mechanism could easily evolve in higher plants too, he suggests. Daniel Chamovitz of Tel Aviv University has discovered a group of genes in plants which sense light or dark and also appear in animals to aid cell division, neuron axon growth, and immune system development.
Smell, too, which is of course the ability to detect chemical compounds in the surrounding medium, has been investigated. When a ripening fruit gives off the pheromone ethylene, nearby unripe ones sense it and will begin ripening also. Smells are crucial to other plant communication, too, which studies have shown to occur often between the roots of different plants by signals of some sort, likely chemical compounds.
Memory among plants has been suggested by some observations. Venus Fly Traps, for example, require two different hairs on the leaves to be touched by a bug before the trap is sprung. The plant must in some fashion register the first signal and “remember” it while waiting for the second.
These findings are of course transitional, as is most science, and continually progressing. But the picture is clear to me – life is finding ways to increase awareness and consciousness, no matter how simple or complex, in order to successfully survive and spread.
I’m hazily reminded of a freshman philosophy course about early nineteenth century German thinkers (I recall being impressed by how they always capitalized their nouns!) Is it possible that Life is discovering itself through Evolution? I should have paid more attention!
