Plants: The Master Chemists of Our Plane
ABSTRACT 摘要
“想象一下，你的双腿被埋在地里，不能走动，也不能说话，你会如何吃东西，如何生长发育，又如何保卫自己呢？这种情况比你想象中更常见：这是植物日常生活中的一部分。植物已经发展出了许多应对策略，这些策略不仅仅是为了他们自身的生存，更是为了与周围的动植物和微生物相互作用。其中一些策略包含运用一些化合物作为植物向周围环境传递的信息。科学家们已经研制出了一些创造性的方法来检测一株植物里含有什么样的化学物质，以及这些化学物质的含量到底有多少。如果我们可以把多样化的植物化合物都辨识出来，在未来我们或许能够更好地理解植物是如何生长的，以及它们是如何与环境相互作用的。同时，我们也许能够运用这些化合物制造药物和生产更健康、更美味的蔬菜。”
Imagine your legs were buried in the ground and you were not able to move or to talk. What would you do to eat, grow, and defend yourself? This situation is more common than you think: It is part of the daily life of plants. Plants have developed many strategies not only to survive, but also to interact with other plants, animals, and microorganisms around them. Some of these strategies involve using chemical compounds that work as messages from the plant to its surroundings. Scientists have developed creative methods to estimate what and how much of a chemical is inside a plant. If we can identify the great diversity of plant compounds, in the future we might be able to better understand how plants grow and interact with their environments. Also, we may be able to use those compounds to make medicines and to produce healthier, tastier vegetables.
植物产生化学物质维持自身生长，同时与周围环境相互作用
PLANTS PRODUCE CHEMICALS TO GROW AND INTERACT WITH THEIR SURROUNDINGS
植物是固着的（sessile），这就意味着它们不能自己随意移动，并永远受限于它们发芽的地方。随着植物的生长，它们必须每时每刻承受周围环境的变化（时而干燥，时而过于湿润）。想一想不同季节的变化或白天晚上的不同天气状况。而且还远远不止这些，植物也需要一些策略与邻居（动植物）相互作用，需要吸引动物来帮助它们传播种子或把它们的花粉传播到另一株植物里。其中一项策略便是植物会分泌大量的化学物质，这种化学物质被称为“代谢产物”。植物代谢产物是可以促进植物生长和与其他生物体相互作用的微量化学物质。
据估计，所有植物加起来会产生10万到100万种代谢产物。为了研究它们，科学家们把代谢产物分成两类：初级代谢产物（primary metabolites）和专有代谢产物（specialized metabolites）。初级代谢产物可在所有植物中寻得，它能帮助植物的生长发育和繁殖。其中一组最为熟知的初级代谢产物是碳水化合物，它可以给植物提供能量以促进植物生长。专有代谢产物对各种各样的植物而言是独一无二的，它可以帮助植物与其他生物体相互作用，在文章的剩余部分我们将把目光聚焦在专有代谢产物中进行讨论。
你是否曾想过植物是如何保卫自己的？植物与食草（以植物为食）昆虫一起生活了数百万年，在这漫长的岁月中，植物已经进化出有毒的防御化合物。例如：当一只昆虫开始吃卷心菜的叶子，植物会增加有毒专有代谢产物的含量，这些有毒专有代谢产物被称为“硫代葡萄糖苷”。它会在之后转化成毒性更强的化合物，这些化合物会使卷心菜叶子尝起来味道不怎么好，从而阻止昆虫继续吃它们。硫代葡萄糖苷于我们而言是非常熟悉的，正是它们赋予了西兰花和萝卜独特的味道。与此同时，昆虫也开创了忍受这些有毒化合物的方法，使它们能够继续吃那些“有毒”的植物。这种植物和昆虫之间持续不断的战斗导致了新型专有代谢产物的进化。
Plants are sessile, which means they cannot move and are permanently restricted to the spot where they germinate. As plants grow, they must cope with an environment that changes all the time (sometimes too dry, some others too wet). Think of the changes in seasons, or the different weather conditions throughout the day and night. As if that is not enough, plants also need to have strategies to interact with their neighbors, to attract animals that help them move their seeds or pollen from one place to another, and to defend themselves from animals that want to eat them. One of the strategies that plants use to do all of that is to produce a great number of chemicals, known as metabolites.Plant metabolites are small chemical compounds that help plants grow and interact with other organisms.
It is estimated that, taken together, all plants produce between 100,000 and 1 million metabolites [1]. To study them, scientists have classified the metabolites into two groups: primary and specialized metabolites. Primary metabolites are found in all plants and help the plants grow, develop and reproduce. One of the most well-known groups of primary metabolites are carbohydrates, which provide plants with energy to grow. Specialized metabolites are unique to different plants and they help plants interact with other organisms. We will focus on specialized metabolites in the remainder of this article.
Have you ever wondered how a plant can defend itself? Plants and herbivore (plant-eating) insects have lived together for millions of years, and during this long time, plants have developed toxic defense compounds. For example, when an insect starts eating the leaves of a cabbage, the plant increases the amounts of toxic specialized metabolites called glucosinolates, which are then converted into even more toxic compounds [2]. These compounds make the cabbage’s leaves taste very unpleasant, discouraging the insects from eating them (Figure 1A). Glucosinolates are very familiar to us, as they give broccoli and radishes their characteristic flavors. At the same time, insects have created ways to tolerate those toxic compounds, allowing them to keep eating those “poisonous” plants. This continuous battle between plants and insects has resulted in the evolution of new specialized metabolites.
图1-植物是如何以及为什么产生专有代谢产物可以帮助我们研发新型药物和农业资源
（A）植物利用专有代谢产物使其远离敌人（食草动物）和朋友（传粉者）。
（B）人类已经学会利用植物代谢产物为我们在药物、化妆品和食物中谋福。
（C）有时，专有代谢产物会有意想不到的结果，如猫薄荷中的荆芥内酯对猫的影响。
Figure 1 - Understanding how and why plants make specialized metabolites may help us develop new medicines and agricultural resources.
(A) Plants use specialized metabolites to keep enemies (herbivores) away and friends (pollinators) nearby. (B) Humans have learned to use specialized plant metabolites for our own benefit in medicines, cosmetics, and foods. (C) Sometimes, specialized metabolites have unexpected effects, like those that the nepetalactones in catnip have on cats.
在其他情况下，植物需要吸引动物来为它们的花授粉，以便它们能够产生种子以保证它们的繁殖（图1A）。传粉者不仅在植物繁殖中不可或缺，而且对人类也尤为重要，因为世界上75%的食物作物是依赖于传粉者的帮助下才能繁殖成功的。植物吸引传粉者的其中一项策略是分泌出一种富含糖分的液体，我们把这种液体称为花蜜。蜜蜂及其他昆虫会停留在植物上吸食花蜜，在吸食花蜜的同时，花粉会附着在它们身体表面。当同一只昆虫停留在其他花朵时，前一朵花的花粉就会在新的花朵中被释放出来，从而保证了种子在未来的萌发。这样，植物就利用造访的昆虫为自身谋取利益。有趣的是，花蜜里不仅含有糖分，而且还含有少量的咖啡因。如果咖啡因的含量高，花蜜的味道就会偏苦涩，它就可以作为植物自身防御的化合物。然而，当含量较低时，它可以作为一种记忆增强剂，刺激昆虫记得回来获取更多的花蜜，进一步确保植物的授粉进程。
In other cases, plants need to attract animals to pollinate their flowers so that they can produce seeds to secure their reproduction (Figure 1A). Pollinators are not only essential for plant reproduction, but they are also important for humans, as 75% of the world’s food crops depend on pollinators for successful production [3]. One of the strategies plants use to attract pollinators is to produce a sugary liquid called nectar. Bees and other insects visit plants to drink the nectar and while doing so, pollen attaches to their bodies. When the same insect visits other flowers, the pollen from the previous plants is released in the new flower, securing future seed production. In this way, plants use the visiting insects for their own benefit. Interesting fact: scientists have found that nectar does not only contain sugar, but also small amounts of caffeine [4]. In high amounts, caffeine is bitter, and it works as a plant defense compound. However, in low amounts, it acts as a memory enhancer, stimulating insects to remember to come back for more nectar and further ensuring the plant’s pollination process.
人类和其他动物利用植物产生的化学物质
HUMANS (AND OTHER ANIMALS) USE CHEMICALS PRODUCED BY PLANTS
人类和其他动物已经学会了利用植物产生的化学物质为它们自身谋取利益。自古以来，人们用植物代谢产物制作药物、天然染色剂、食品和化妆品的原料以及许多其他用途。（图1B）
Humans and other animals have learned to use chemicals produced by plants for their own benefit. Since ancient times, people have used plant metabolites as medicines, natural dyes, and ingredients in food and cosmetics, amongst many other uses (Figure 1B).
阿片（opium）是最古老的植物提取物之一，是从罂粟科罂粟属植物（俗称罂粟）中提取出来的混合化合物。它曾被用作被蛇、蜘蛛咬伤或被蝎子蜇伤的解毒药。如今，吗啡（在阿片众多化学物质中的其中一种化学物质）是被用来减轻痛苦的处方药物。皂素是另一个广为人知的植物化合物被人类利用的例子。皂素存在于不同种类的植物和树木中，它们会分泌出令人作呕的化合物从而昆虫会对其远离而吃不到叶子。世界各地的土著人也都会普遍利用这些含有丰饶皂素植物的提取物制作天然香皂。
One of the oldest plant extracts is opium, a mix of chemical compounds extracted from the plant Papaver somniferum, commonly known as the poppy, which was used as an antidote against snake and spider bites and scorpion stings. Today, morphine, one of the many chemicals found in opium, is prescribed to alleviate pain. Saponins are another well-known example of plant compounds used by humans. Saponins are present in a variety of different plants and trees, where they work as nasty compounds that keep insects away from eating plants’ leaves (Figure 1A) [5]. Also, indigenous people from around the world have commonly use saponin-rich plant extracts as natural soap.
植物代谢产物也可以影响其他动物的行为。猫薄荷（Nepeta cataria）会产生一种被称为荆芥内酯（nepetalactone）的化合物。当猫咪靠近去闻这种植物时，会变得十分爱嬉戏和心旷神怡（图1C）。荆芥内酯通常与植物的防御有密切联系，然而科学家们也还未能完全明白它的角色。在未来的研究中，研究植物是如何产生荆芥内酯的，可以帮助科学家研发具有镇定和放松特性的新型药物或用于农业领域生产的新型生物杀虫剂。
Plant metabolites can also influence the behavior of other animals. Catnip (Nepeta cataria) produces a compound known as nepetalactone. When cats sniff this plant, they become very playful and relaxed (Figure 1C). Nepetalactone is commonly associated with plant defense; however scientists do not yet fully understand its role. Future research on how plants make nepetalactone could help scientists develop new medicines with sedative and relaxant properties, or new bio-insecticides for agriculture.
我们离鉴别出所有植物代谢产物以及了解植物是如何产生它们的还很遥远。然而，在过去的十年里，科学技术的发展使科学家们能够发现更多的植物代谢产物。在下一节里，我们将探索科学家们是如何分离和鉴别这些物质的。
We are still far from identifying all plant metabolites and even further from understanding how plants produce them. However, in the last decades, technological developments have allowed scientists to discover more plant metabolites. In the next section, we will explore how scientists isolate and identify these substances.
科学家们是如何鉴别和研究植物化学药物呢？
HOW DO SCIENTISTS IDENTIFY AND STUDY PLANT CHEMICALS?
由于专有代谢产物对植物尤为重要，对我们也相当有用，科学家们研发了几种检测它们的方法。人类将专有代谢产物从植物中提取出来已经有很长一段时间了。冲泡咖啡是提取的一个典型例子。概念很简单明了：植物原料（如研磨的咖啡豆）与一种被称为溶剂的液体（就咖啡而言，它的溶剂是热水）混合，以便提取出代谢产物。一段时间后，溶剂会吸收咖啡豆里所含代谢产物的颜色和味道。紧接着将这些混合物过滤，将固体植物原料丢弃，余下的溶剂就含有植物代谢产物的提取物。
科学家们运用同样的原理提取和研究了许多植物代谢产物。为了鉴别专有代谢产物，科学家们必须考虑到它们的物理性质和化学性质，如代谢产物是否溶于水或是否还需要另一个不同的溶剂。得到过滤后的提取物是提取过程的最后一个步骤，接下来的步骤便是分离和鉴别提取物中呈现的化合物。
Since specialized metabolites are so important for plants and quite useful for us, scientists have developed several ways to measure them. Humans have extracted specialized metabolites from plants for a very long time. Brewing coffee is one example of extraction. The concept is simple: plant material, for example ground coffee beans, is mixed with a liquid called a solvent (hot water, in the case of coffee) to allow the extraction of metabolites. After some time, the solvent takes up the flavor and color of the metabolites contained in the coffee beans. The mixture is then filtered and the solid plant materials are discarded, while the liquid solvent contains an extract of plant metabolites.
Scientists have applied this same principle to extract and study many plant metabolites. To identify specific metabolites, scientists must consider their chemical and physical properties, such as whether the metabolites can dissolve in water or whether a different solvent is needed. Obtaining the filtered extract is the last step of the extraction process (Figure 2A). The next steps are the separation and identification of the chemical compounds present in the extract.
Figure 2 - Plant metabolites are analyzed using chromatography and mass spectrometry.
图2-用色谱法和质谱法验定植物代谢产物
(A) The first part of the analysis is the preparation of the sample. In this example, leaves are ground up and mixed with a solvent in a tube.
（A）验定的第一部分是样品的制备。在本例中，叶子被研磨成碎片，将碎叶与管中的溶剂混合
(B) Using chromatography, the liquid part from the previous step is analyzed and the metabolites in the leaves are separated.
（B）利用色谱法，可将上一步骤的液体部分进行验定，分离出叶片中的代谢物。
(C) Using mass spectrometry, plant metabolites are further broken apart (ionization) and a detector registers the number and identity of the parts of metabolites that come out.
（C）利用质谱技术，将植物代谢物进一步裂解（电离），由检测器记录出代谢物各部分的数量和特性。
色谱法是一项用于分离许多化合物的技术（图2B）。要被分离的代谢产物混合液体被称为“流动相”（包含在图2A中的管中）。流动相流经第二种物质，我们把这种物质称为“固定相”（图2B的蓝色部分）。在流动相里的代谢产物（植物提取物）会与固定相以不同的方式相互作用。一些代谢产物在流经固定相时速度较慢，一些则较快，这就导致了各种各样的代谢产物的分离。每种代谢产物流经时间不同，是科学家们利用其鉴别代谢产物的标志之一。
Chromatography is a technique used to separate chemical compounds (Figure 2B). The liquid mixture of metabolites to be separated is called the mobile phase (contained in the tube in Figure 2A). The mobile phase is then flowed through a second substance called the stationary phase (colored blue in Figure 2B). The metabolites in the mobile phase (plant extract) will interact with the stationary phase in different ways. Some metabolites will move slowly through the stationary phase and others will move more quickly, causing the various metabolites to separate. The different travel time of each metabolite is one of the signatures that scientists use to identify them.
一些植物代谢产物只需运用色谱法便可以轻而易举地被鉴别出来。然而，植物代谢产物可能会十分复杂。这些复杂性会使鉴别变得非常艰难，有时候就需要通过其他途径来帮助鉴别它们。质谱法是一项将代谢产物进一步裂解，然后将不同的部分（称为离子）分离出来，以检测它们在化合物中存在的数量的技术（图2C）。质谱仪主要由三个主室构成。在第一室中，代谢产物被裂解成它的基本组成部分，称为离子。离子通过第二室（被称为质量分析器）到达第三室（检测器）。每个离子的质量和通过质量分析器所需要的时间都被检测器记录下来，从而提供关于离子特性的十分详尽的信息。可以将色谱法和质谱法结合在一台功能强大的机器上，以检测微少的专有代谢产物。
Some plant metabolites can be easily identified using chromatography alone. However, plant metabolites can be extremely complex. This complexity makes their identification difficult, and other methods are sometimes required to identify them. Mass spectrometry is a technique that breaks metabolites down further and then separates the different parts (called ions) to detect how many of them are present in a chemical compound (Figure 2C). A mass spectrometer is usually composed of three main chambers. In the first chamber, the metabolite is disintegrated into its essential parts, called ions. The ions race through the second chamber, called the mass analyzer, to reach the third chamber, called the detector. The mass of each ion and the time taken to travel through the mass analyzer is recorded by the detector, providing extremely specific information about the ion’s identity. Chromatography and mass spectrometry can be combined in a single, powerful machine to detect very small amounts of specialized metabolites.
接下来是什么呢？
WHAT IS NEXT?
我们已经向你展现了一些关于植物代谢产物多样性和它的用途的例子，并解释了科学家们是如何分离和鉴别它们的。如今已经发现了许多植物代谢产物，除了对植物自身十分重要之外，一些化合物对人类也十分有利用价值。还有许多植物代谢产物有待发现和探索，每年科学家都会发现新的代谢产物。了解植物里的化学物质不仅是一件振奋人心的事，而且能帮助我们发现新型药物和农业资源。尽管我们对很多植物代谢产物的功能还不完全了解，但这些化合物代表着一个巨大的应用潜能宝库。这些化合物的丰富多样使植物成为我们星球的大师化学家。
We have shown you just a few examples of the great diversity and uses of plant metabolites and explained how scientists isolate and identify them. Many plant metabolites have already been discovered and, in addition to being important to the plants that make them, some of the compounds are also useful to humans1. There are still plenty more plant metabolites to be discovered and explored, and every year scientists discover new ones. Understanding plant chemicals is not only exciting, but it also helps us to develop new medicines and agricultural resources. Although the functions of many plant metabolites are still not understood, these compounds represent a huge reservoir of potential applications. This great diversity of chemical compounds makes plants the master chemists of our planet.
Glossary 术语表
Metabolite: ↑ Small chemical compound that helps plants grow and interact with other organisms.
代谢产物：帮助植物生长和与其他生物体相互作用的微量化合物
Glucosinolates: ↑ Specialized metabolites with pungent taste, present in plants, such as broccoli, radish, and mustard.
硫代葡萄糖苷：存在于如西兰花、萝卜、芥菜等植物，是一种具有刺激性气味的代谢产物
Saponins: ↑ Specialized metabolites traditionally used as natural detergents. The name comes from the Latin word “sapo” which means soap. A very important saponin mix, called QS-21, comes from the Chilean tree Quillaja saponaria, and it is used as an ingredient in formulation of vaccines.
皂素：传统上用作天然洗涤剂的专有代谢产物。其名源于拉丁语“sapo”，是肥皂的意思。一种被称为QS-21的非常重要的皂素混合物，它来自智利的皂树，被用作疫苗配方中的一种成分。
Nepetalactone: ↑ Specialized metabolite found in the catnip plant, Nepeta spp.that attracts and alters the behavior of cats making them relaxed and playful.
荆芥内酯：在猫薄荷中发现的专有代谢产物。它能吸引和改变猫咪的行为，使猫咪变得更加爱嬉戏、更加心旷神怡。
Extraction: ↑ The process by which plant metabolites are separated and isolated from any other compounds present in plant material.
提取：将植物代谢产物从任何其他呈现在植物材料里的化合物中分离提取出来的过程。
Solvent: ↑ In chromatography the solvent is the liquid where plant metabolites are placed. This solution (solvent plus metabolites) flows through chromatography for separation.在溶剂：色谱法中，溶剂是提取植物代谢物所需的液体。这种溶液（溶剂+代谢物）流经色谱法进行分离。
Chromatography: ↑ A separation technique commonly used to separate a mix of compounds
色谱法：一项普遍用于分离混合化合物的分离技术。
Mass Spectrometry: ↑ A technique to measure the mass and charge of ions from molecules present in a solution.
质谱法：一种测量溶液中分子离子呈现的质量和电荷的技术。
—The End—
附上作者信息：
当我还是一位在哥伦比亚读生物学的学生时，我对植物及其化学的热情油然而生。在我完成本科学位后，我决定将我的科学生涯聚焦于了解植物是如何调节初级代谢产物和专有代谢产物的产生。我参加了一些科学项目，这些项目不仅激发了我对了解植物新陈代谢和生理学的兴趣，而且还激发了我对如何提高植物的生产力和用途的兴趣。我坚信，我们可以从植物身上学到更多的东西，而且我与植物接触会产生许多乐趣。我目前在Keygene工作，这是一家位于荷兰的农业生物技术公司。
我对植物以及它们能生产出如此多的化合物的能力非常着迷。为了更好地理解植物是如何以及为为什么成为资深的化学家，我利用分子生物学研究植物的基因，利用代谢组学研究植物的化合物。我研究了马铃薯和西红柿植物中被称为甾体生物碱的苦味化合物的生物合成，现在我又研究了被称为皂素的皂类植物防御化合物。我们越是了解植物是如何以及为什么制造化合物，就越能更容易开发出有用的产品，以实现一个可持续发展的社会。
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