【英语语言学习】蔬菜们的生物钟

This is SCIENCE FRIDAY. I'm Ira Flatow. You open the door of your fridge and the light goes on, right? What if the light in your fridge could stay on and be programmed to help your veggies taste better or be more nutritious¹? Why? Well, it turns out that that head of cabbage on your grocery shelf isn't just sitting there as long as it's not too far after harvesting. Researchers have found that it can still respond to daily cycles of light and darkness and build up its own circadian rhythms, changing its biochemistry to adapt to the daily cycles.

 

Why is that important? Joining me now is Janet Braam. She is chair and professor of biochemistry and cell biology at Rice University in Houston and one of the authors of a paper published this week on this research in the journal Current Biology. Welcome to the program.

 

DR. JANET BRAAM: Thank you.

 

FLATOW: So our veggies are sitting there in the supermarket, and they're doing what?

 

BRAAM: Well, they are still alive. They are still responding to external stimuli². What we've shown is perhaps surprisingly, they can respond to light-dark cycles and really change their metabolite accumulation to different times of day.

 

FLATOW: They change their metabolism³ as the sort of a circadian rhythm for my cabbage?

 

BRAAM: Right, right. So when the crops are growing in the field, they respond to the light-dark cycles, and they - all plants have a circadian rhythm, so they have patterns of behavior that they control or they - that are under the influence of their circadian clock. And when you harvest vegetables and fruits, these vegetables and fruits really stay very much alive even though they've been removed from the whole plant. But then when we store them under constant conditions like in constant light in the grocery store, their circadian rhythms begin to dampen. And so then they lose the ability to show these rhythmic⁴ behaviors.

 

FLATOW: And when they're doing the rhythmic behaviors, there's got to be a good reason why they're in a behavior; they're doing something.

 

BRAAM: Right. We know from basic plant biology research that plants have these circadian clocks, and we know that they use them in part to respond or to prepare for seasonal⁵ changes. But in addition, we recently found that these circadian clocks are also very important for plant defense⁶ against insect attack. So plants are able to turn on their defenses at a time when insects are most likely to seed. So in that way, they can prepare for attack before it actually happens. And this is clearly advantageous⁷. Plants are much more resistant⁸ to insects if their clocks are functioning properly.

 

FLATOW: And when they get - when you put them under the 24-hour harsh light of a grocery stand, you just wrecked⁹ that whole circadian rhythm?

 

BRAAM: Right. The plants are confused. They don't know what time - when it's day and when it's night, and so their circadian rhythms dampen and go away.

 

FLATOW: And so they may lose that ability to fight off bugs¹⁰ that might land on them?

 

BRAAM: Yes. Their ability to fight off bugs has certainly decreased when their circadian rhythms are lost.

 

FLATOW: Do they also, during this cycle, get - put out stuff that makes them more nutritious for us at any one point in that cycle?

 

BRAAM: Well, what we've shown is that with cabbage, cabbage is related to the research plant that we work on, that research plant makes these particular chemical compounds that send off insects. So the insects don't like to eat the plants...

 

FLATOW: Right.

 

BRAAM: ...because these chemicals taste bad or make the insects sick. But these same chemicals that are in our model plants are also in things like cabbages and broccoli¹¹, cauliflower. And what we've shown is that those chemicals accumulate with circadian periodicity in these post-harvest vegetables just like they do in our model plant. But in - for us, eating these vegetables like cabbage, those chemical compounds are - have been found to be potent¹² anti-cancer compounds. So they have anti-cancer activities.

 

FLATOW: You mean like antioxidants, things like that?

 

BRAAM: Yes. Some of them are antioxidants or they activate¹³ antioxidant processes in our cells.

 

FLATOW: So...

 

BRAAM: And so - yeah.

 

FLATOW: Yeah. So I guess, ideally, if you wanted to keep all that going, you would have the lights in the supermarket go on and off for like just mimicking¹⁴ daylight.

 

BRAAM: Right. So look - yeah.

 

FLATOW: And when you brought it home, if you put it in the refrigerator, you might do the same thing.

 

BRAAM: Right. That's one possibility from - that you might make - have a conclusion from our research. So we showed that if you take these post-harvest cabbage and put them under light-dark cycles, these chemical compound cycles - dependent on time of day - and then it might make a difference at what time of day you actually eat your vegetables. You could plan to eat it at the time of day when those chemicals are at their optimal¹⁵ level.

 

FLATOW: Do you know what time of day that is?

 

BRAAM: We've only just begun to look at this, right? So we've only used one kind of treatment of 12 hours of light and 12 hours of darkness. And we've only looked at cabbage so far. And under our experimental conditions, we find that these chemicals accumulate most in the day, it may be midday, and they go down at night. And there's about a two-fold difference.

 

FLATOW: Wow.

 

BRAAM: But much more would need to be done to know really when the best time of day would be to eat different kinds of vegetables.

 

FLATOW: OK. So you started with cabbage. Are there any other veggies that look enticing¹⁶, so to speak, for you to study or sort of similar to a cabbage cycle?

 

BRAAM: Well, what we did after we found that this result worked with cabbage, we decided¹⁷ to try to see how broad a phenomenon this might be. We started with other leafy vegetables like spinach¹⁸ and lettuce¹⁹, and we could show that in the lab, we could re-entrain their circadian rhythms also. And then since those worked, we then went back to the grocery store and bought things like zucchini and blueberries and sweet potatoes and carrots. And of all these we could show could perceive these light-dark signals and reactivate their clock and show rhythmic behaviors.

 

FLATOW: Mm-hmm. Now, I'm picturing a big head of cabbage. And, you know, cabbage has lots of leaves on it.

 

BRAAM: Yes.

 

FLATOW: Is the light only getting to the outermost²⁰ leaves, or does it filter into the inner leaves as, you know, does it work on the circadian rhythm on the entire cabbage, and where is the clock located in the cabbage?

 

(LAUGHTER)

 

BRAAM: So cabbage is made of a collection of leaves and some of the leaves are on the outside. And I would imagine that under certain circumstances where there's just light shining on the head of cabbage...

 

FLATOW: Yeah.

 

BRAAM: ...probably only the outer leaves are perceiving those lights signals. However, the circadian clock can also be sent by - set by temperature changes. And so in the field, if this cabbage is growing, I would imagine both the inner and outer leaves maintain their circadian rhythmicity. But we really haven't looked at any of that yet. So these are just speculation²¹ on my part. But in plants, the circadian clock or each individual cell is believed to have a circadian clock. And they all run autonomously²² or mostly autonomously. And so they all get set in synchrony by these external stimuli.

 

FLATOW: Yeah. So what you're saying in terms of the fewer, even a gardener or someone who has plants, that it's not healthy for the plant to keep it under the light 24 hours a day. If you want to grow it in your basement or, you know, some place, you got to give them some dark time. You have to give them some circadian rhythm.

 

BRAAM: Our work with - yeah. Right. Our work would suggest that especially with defense against insects and fungi²³ that circadian periodicity is important to maintain. So keeping a light-dark cycle would be important.

 

FLATOW: Mm hmm. Don't just keep those grow lights on all the time.

 

That's right.

 

(LAUGHTER)

 

FLATOW: All right. So where do you go from here? What would be your next step?

 

BRAAM: Well, we're interested in understanding, one, what are all the metabolites or small molecules²⁴ that are under the control of the circadian clock in these post-harvest vegetables and fruits? So in things like zucchini and carrots and sweet potato, we would expect a different sweet of metabolites to be regulated by the clock. So we'd like to know what those are. And then we'd like to know what kind of conditions could be used to make this a practical - if it turns out that we can really make a difference in nutritional²⁵ quality then...

 

FLATOW: Right.

 

BRAAM: ...we would want to design a simply way to keep the clock running. And we know that plants can respond to just pulses of light in ways that can control or set their clock. And so we'd like to investigate what are the simplest ways that we can use to make this practical.

 

FLATOW: Well, we wish you good luck, Dr. Braam.

 

BRAAM: Thank you very much.

 

FLATOW: Thank you for taking time to be with us today.

 

BRAAM: Thank you.

 

FLATOW: Janet Braam is chair and professor of biochemistry and cell biology at Rice University in Houston.

1 nutritious   

adj.有营养的，营养价值高的

参考例句：

• Fresh vegetables are very nutritious.新鲜蔬菜富于营养。
• Hummingbirds have discovered that nectar and pollen are very nutritious.蜂鸟发现花蜜和花粉是很有营养的。

2 stimuli   

n.刺激（物）

参考例句：

• It is necessary to curtail or alter normally coexisting stimuli.必需消除或改变正常时并存的刺激。
• My sweat glands also respond to emotional stimuli.我的汗腺对情绪刺激也能产生反应。

3 metabolism   

n.新陈代谢

参考例句：

• After years of dieting,Carol's metabolism was completely out of whack.经过数年的节食，卡罗尔的新陈代谢完全紊乱了。
• All living matter undergoes a process of metabolism.生物都有新陈代谢。

4 rhythmic   

adj.有节奏的，有韵律的

参考例句：

• Her breathing became more rhythmic.她的呼吸变得更有规律了。
• Good breathing is slow,rhythmic and deep.健康的呼吸方式缓慢深沉而有节奏。

5 seasonal   

adj.季节的，季节性的

参考例句：

• The town relies on the seasonal tourist industry for jobs.这个城镇依靠季节性旅游业提供就业机会。
• The hors d'oeuvre is seasonal vegetables.餐前小吃是应时蔬菜。

6 defense   

n.防御，保卫；[pl.]防务工事；辩护，答辩

参考例句：

• The accused has the right to defense.被告人有权获得辩护。
• The war has impacted the area with military and defense workers.战争使那个地区挤满了军队和防御工程人员。

7 advantageous   

adj.有利的；有帮助的

参考例句：

• Injections of vitamin C are obviously advantageous.注射维生素C显然是有利的。
• You're in a very advantageous position.你处于非常有利的地位。

8 resistant   

adj.(to)抵抗的，有抵抗力的

参考例句：

• Many pests are resistant to the insecticide.许多害虫对这种杀虫剂有抵抗力。
• They imposed their government by force on the resistant population.他们以武力把自己的统治强加在持反抗态度的人民头上。

9 wrecked   

adj.失事的，遇难的

参考例句：

• the hulk of a wrecked ship 遇难轮船的残骸
• the salvage of the wrecked tanker 对失事油轮的打捞

10 bugs   

adj.疯狂的，发疯的n.窃听器( bug的名词复数 )；病菌；虫子；[计算机]（制作软件程序所产生的意料不到的）错误

参考例句：

• All programs have bugs and need endless refinement. 所有的程序都有漏洞，都需要不断改进。 来自《简明英汉词典》
• The sacks of rice were swarming with bugs. 一袋袋的米里长满了虫子。 来自《简明英汉词典》

11 broccoli   

n.绿菜花，花椰菜

参考例句：

• She grew all the broccoli plants from seed.这些花椰菜都是她用种子培育出来的。
• They think broccoli is only green and cauliflower is only white.他们认为西兰花只有绿色的，而菜花都是白色的。

12 potent   

adj.强有力的，有权势的；有效力的

参考例句：

• The medicine had a potent effect on your disease.这药物对你的病疗效很大。
• We must account of his potent influence.我们必须考虑他的强有力的影响。

13 activate   

vt.使活动起来，使开始起作用

参考例句：

• We must activate the youth to study.我们要激励青年去学习。
• These push buttons can activate the elevator.这些按钮能启动电梯。

14 mimicking   

v.（尤指为了逗乐而）模仿( mimic的现在分词 )；酷似

参考例句：

• She's always mimicking the teachers. 她总喜欢模仿老师的言谈举止。
• The boy made us all laugh by mimicking the teacher's voice. 这男孩模仿老师的声音，逗得我们大家都笑了。 来自辞典例句

15 optimal   

adj.最适宜的；最理想的；最令人满意的

参考例句：

• What is the optimal mix of private and public property rights in natural resources?私人和国家的自然资源产权的最适宜的组合是什么？
• Optimal path planning is a key link for the sailing contest.帆船最优行驶路径规划是帆船比赛取胜的关键环节。

16 enticing   

adj.迷人的；诱人的

参考例句：

• The offer was too enticing to refuse. 这提议太有诱惑力，使人难以拒绝。
• Her neck was short but rounded and her arms plump and enticing. 她的脖子短，但浑圆可爱；两臂丰腴，也很动人。

17 decided   

adj.决定了的，坚决的；明显的，明确的

参考例句：

• This gave them a decided advantage over their opponents.这使他们比对手具有明显的优势。
• There is a decided difference between British and Chinese way of greeting.英国人和中国人打招呼的方式有很明显的区别。

18 spinach   

n.菠菜

参考例句：

• Eating spinach is supposed to make you strong.据说吃菠菜能使人强壮。
• You should eat such vegetables as carrot,celery and spinach.你应该吃胡萝卜、芹菜和菠菜这类的蔬菜。

19 lettuce   

n.莴苣；生菜

参考例句：

• Get some lettuce and tomatoes so I can make a salad.买些莴苣和西红柿，我好做色拉。
• The lettuce is crisp and cold.莴苣松脆爽口。

20 outermost   

adj.最外面的，远离中心的

参考例句：

• He fired and hit the outermost ring of the target.他开枪射中了靶子的最外一环。
• The outermost electron is shielded from the nucleus.原子核对最外层电子的作用受到屏蔽。

21 speculation   

n.思索，沉思；猜测；投机

参考例句：

• Her mind is occupied with speculation.她的头脑忙于思考。
• There is widespread speculation that he is going to resign.人们普遍推测他要辞职。

22 autonomously   

adv. 自律地，自治地

参考例句：

• To learn autonomously in the network environment is totally new to students. 基于网络环境下的自主学习对学生来说，是一种全新的学习方式。
• The QC-RS can operate autonomously or by remote control. QC-RS能实现自动操作或通过遥控来操作。

23 fungi   

n.真菌，霉菌

参考例句：

• Students practice to apply the study of genetics to multicellular plants and fungi.学生们练习把基因学应用到多细胞植物和真菌中。
• The lawn was covered with fungi.草地上到处都是蘑菇。

24 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

25 nutritional   

adj.营养的，滋养的

参考例句：

• A diet lacking in nutritional value will not keep a person healthy.缺乏营养价值的饮食不能维持人的健康。
• The labels on food products give a lot of information about their nutritional content.食品上的标签提供很多关于营养成分的信息。