We tend to think plants are rather simple, unaware entities. The truth is that they are quite sophisticated and tuned in to what is happening around them. In addition to photosynthesis, itself a complex chemical process, plants have their own way of mimicking many of the sensory functions that mammals have.
Plants must sense the direction, amount, duration, and color of light to survive. For instance, to turn red, poinsettias (Euphorbia pulcherrima) must have a sufficient amount of uninterrupted dark, and Christmas cacti (Schlumbergera bridgesii) require a dark period to bloom. Plants use blue light detection to bend towards a light and red light to determine when to flower. Plant nurseries use exposure to red light to control when chrysanthemums (Dendranthema maximum) bloom. Some species’ seed will not sprout unless exposed to light.
Plants have a function somewhat like hearing. In a 2014 study, scientists played the recorded sounds of an insect chewing on a plant leaf in an enclosed space with a plant. The plant produced chemicals that deter that particular kind of insect from eating its leaves. An unexposed control plant did not increase production of the chemical.
Plants also send out gaseous signals in the air when they are under attack. These signals not only attract beneficial insects that prey on the attacking insect, but also alert downwind plants to start producing protective chemicals. In effect, the other plants can “smell” the warning signal.
Plants are very sophisticated chemical factories, producing a wide range of chemicals. We are urged to eat vegetables because of their antioxidants, such as lutein, anthocyanins, and carotenoids. These chemicals play a wide range of functions in the plant, such as deterring insect pests by scent, bitter taste, and poison.
How about the sense of touch? Plants know when they are touched and can tell hot from cold. The Venus flytrap (Dionaea muscipula) snaps closed when an insect touches two of its hairs and can distinguish between the touch of rain or an insect. A mimosa (Mimosa spp.) will fold up its leaflets when touched. Some vines send out tendrils that tend to whip around in the air—until it comes in contact with another object. Then the plant responds to that “touch” by wrapping itself tightly around the other object.
Plants also have a memory-like function. An insect must touch the second hair of the Venus flytrap within 20 seconds of the first hair touched to trigger the trap, so the plant must store the information about the first touch. Some plants require a period of cold before they can flower, or their seed may require a cold period to germinate, so the plant must recall that it experienced the required period of cold.
Plants can form partnerships. They have a mutually beneficial relationship with a kind of soil fungi called mycorrhizae. These mycorrhizae attach to the plant’s roots and then spread-out long filaments called mycelia throughout the soil. The fungi are particularly good at taking in phosphorus, with which plants have difficulty. In return, the plant shares the carbohydrates it produces through photosynthesis with the fungi, which cannot photosynthesize.
Once a plant has developed this partnership with the fungal network, the plant can use it to share nutrients with other plants. Interestingly, some plants do not limit sharing to members of their own species. Some scientists call this network the “Wood Wide Web.”
Plants also use this fungal network to communicate chemically with other plants. In effect, plants have their own gossip network. If one plant is attacked, it can communicate that with the other plants in its extended neighborhood via the Wood Wide Web. The other plants then develop defensive chemicals.
Plants are even more sophisticated than what I explain here. Space limitations preclude an explanation of the complex science behind these capabilities. If you would like to learn more, good sources are Daniel Chamovitz’s “What a Plant Knows: A Field Guide to the Senses” and Linda Chalker-Scott’s “How Plants Work: The Science behind the Amazing Things Plants Do.”
February 25, 2021 at 12:32AM
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GARDENING WITH THE MASTERS: My plant can do what?: Sophisticated senses and signals - Cherokee Tribune Ledger News
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