Passage 4 Memories in Nature
植物也有记忆 《纽约时报》

[00:01]We tend to think of memory as unique to animals. But it isn't.
[00:08]Plants also have a form of memory. Yes: they, too,
[00:13]are shaped by what happens to them,
[00:16]and alter their responses to future events based on
[00:20]their experiences in the past. As an example, consider wild tobacco,
[00:28]Nicotiana sylvestris. (This is not the plant we cultivate for cigarettes,
[00:35]but one of its ancestors:
[00:38]domestic tobacco is thought to be a hybrid of several species,
[00:43]including Nicotiana sylvestris and Nicotiana tomentosiformis.)
[00:50]Like all plants, wild tobacco has a problem. It can't move to
[00:56]escape from its enemies - the caterpillars and other animals
[01:00]that enjoy eating its leaves.
[01:04]It can, however, act to discourage them. It can discover damaged leaves;
[01:11]in response, it produces nicotine. The nicotine travels from the roots
[01:18](where it is made), through the sap and into the leaves.
[01:23]Nicotine apparently doesn't taste good:
[01:26]caterpillars fed on leaves from plants that recently experienced damage
[01:32]and so are high in nicotine eat much less than caterpillars
[01:37]fed on leaves from previously undamaged plants.
[01:42]But here's the interesting part. Tobacco plants attacked for the first time
[01:48]take longer to mount their defense than tobacco plants
[01:52]that have previously experienced an attack.
[01:56]This isn't because the previously attacked plants
[01:59]keep on producing a higher level of nicotine - they don't.
[02:05]Nicotine is expensive for a plant to make (it takes a lot of energy
[02:10]and requires large amounts of nitrogen,
[02:14]which the plant might prefer to use for other purposes),
[02:19]so they only do it when necessary. No:
[02:24]the previously attacked plants respond to new leaf damage more quickly.
[02:30]And plants that have been attacked twice are faster to respond than plants
[02:36]that have only been damaged once. Somehow, they remember.
[02:42]The physical basis of plant memory is still being figured out.
[02:48](Needless to say, it isn't conscious memory:
[02:52]the trees outside your window aren't standing there reminiscing
[02:56]to themselves about the great caterpillar plague of 2009.)
[03:03]But by now it's clear that wild tobacco is not the only plant
[03:08]with the capacity for memory, nor is caterpillar attack the only stress
[03:14]that produces such an effect.
[03:17]Drought, cold and altered salt levels in the soil all do so;
[03:24]likewise, exposure to hostile fungi or bacteria.
[03:28]If plants remember - can they also forget? As far as I can tell,
[03:36]no one knows the answer to this yet.
[03:40]Nor does anyone know how many different kinds of stresses
[03:44]a plant can keep track of at once. But the subject is important,
[03:51]as the stresses plants are exposed to can affect how well they grow.
[03:58]Being able to prime them to respond to pests,
[04:02]or enable them to forget about a drought,
[04:05]could have big implications for agriculture.