What Plants Know

October 23rd, 2012

    We tend to think of plants as not very smart living things.

Plants are more like us than we think.

   They’ve alive in the sense that we can kill them (and boy, are some of us good at that), but when it comes to “knowing” things, plants are more like rocks than people or pets.

   Or are they?

   A fascinating new book by Israeli bioscientist Daniel Chamovitz takes us into the inner workings of plants (“What a Plant Knows,” Scientific American, $23). What he’s found shows that plants really do – in their own way – see, talk, smell and even remember.

   If you stop and think, you’ve seen this in action. A plant must sense light and dark somehow since they grow differently in differing light. You’ve probably heard stories about how some people are sure their plants grow better when they “talk nice” to them.

   What you might not realize is that plants do these kinds of things in ways that aren’t that different from humans.

   Plants might not have noses and mouths, but they do respond to hormonal scents and send signals to other plants.

   Chamovitz got involved by researching how plants responded to light. He isolated the genes that regulate light response, and to his surprise, they were in the same group of genes that regulate cell division and immune response in humans.

   “This led me to realize that the genetic difference between plants and animals is not as significant as I had once naively believed,” he told Scientific American magazine.

   Take smell. Chamovitz points to the classic example of how if you put bulbs in the refrigerator next to apples, the bulbs will ripen and possibly rot.

   Something similar happens in a fruit grove when the first few fruits start to ripen and then induce neighboring fruits to do likewise.

   Florida fruit growers figured something stranger was at work than simple warmth when they tried to ripen citrus in storage sheds. The fruits ripened when they used kerosene heaters but not when they used electric heaters.

   The reason behind all of these is ethylene. It’s a plant hormone that triggers ripening, and it emanates from sources such as ripening apples and kerosene smoke.

   Even beyond that, Chamovitz says a weedy parasite called dodder actually picks host plants by smell. When you place dodder next to wheat and tomatoes, it goes for the tomatoes every time because of the odor differences.

   When it comes to communicating, plants don’t exactly talk, text or Tweet. But Chamovitz says that when a maple tree gets attacked by a bug, it does release a pheromone that other nearby maples can pick up.

   “This induces the receiving trees to start making chemicals that will help them fight off the impending bug attack,” he says.

   Another recent study found that drought-stressed plants were able to “warn” neighboring plants to get ready for a lack of water via root-to-root signals. When plants were separated by growing them in pots, the same signal-passing didn’t happen – kind of like they have a wired Internet connection but not Wi-Fi.

   Then there’s the sense of touch. Research has found that seedlings grow stockier when a wind-stimulating fan blows over them, and tree roots develop faster when subjected to the effects of real wind.

   Both make sense because the response helps the plants survive a sensed blow-over threat.

   Just like humans, Chamovitz says plants have a short-term memory, an immune memory and even memory handed down from generation to generation (family history, if you will).

   Example: A venus fly trap will snap shut only when two of its leaf hairs are touched. That means it has to keep track of when the first hair gets touched. It turns out this “memory” lasts only 20 seconds, because if the second touch doesn’t happen in that time frame, the mechanism rewinds.

   He says that wheat seedlings “remember” the winter they’ve gone through before deciding when to flower, and stressed plants produce baby plants that often have an increased resistance to that stress.

   All of this doesn’t exactly mean that plants “think,” Chamovitz says. Neither do they feel pain when you prune them.

   And sorry to burst your music bubble, but plants are least like us when it comes to hearing. Chamovitz says research hasn’t borne out any evidence that plants like music or that they’ll thrive amidst Muzak but curl up when Led Zeppelin comes on.

   They are, however, “complex organisms that live rich, sensual lives,” Chamovitz concludes.

   We may treat them as inanimates, but from what Chamovitz says, you could make a good argument that they’re often smarter than the family dog.

Sidebar

   If plants are more like us than we think, what might be going on in their little botanical “minds?” George Weigel takes a fun look at that in this little e-column.

   For more on Daniel Chamovitz’s plant observations, visit www.whataplantknows.com.