Veggies pack lots of nutrients. But our bodies need some nutrients that can be found only in animal products, such as meat and milk. Now, researchers have tweaked' the genes in leaves so that plants, too, can at last make some of these compounds. This might one day let vegetarians and vegans rely on plants for the full range of nutrients their bodies need.

蔬菜富含多种营养，但人体所需的某些营养素只能从肉类、牛奶等动物产品中获取。如今，研究人员通过微调植物叶片的基因，使植物最终也能合成部分动物源性营养素。未来，素食主义者和纯素食者或许可以依靠植物获取身体所需的全部营养。

“My mom is a vegetarian," says Pengxiang Fan. "So I started looking at what I can do to improve the plant-based diet."A biochemist, Fan works at Zhejiang University in Hangzhou, China.

“我妈妈是素食主义者，”范鹏祥说，“所以我开始研究如何改善植物性饮食。”范鹏祥是一位生物化学家，在中国杭州的浙江大学工作。

Enzymes are proteins that speed up chemical reactions inside living things. To pump out the animal-type nutrients,plant leaves need enzymes they don't normally have. In this case, they need enzymes that help turn certain amino acids--the building blocks of pro.teins-into compounds normally found only in meat.

酶是能够加速生物体内化学反应的蛋白质。为了合成动物源性营养素，植物叶片需要它们通常不具备的酶。具体来说，它们所需的那类酶能够将某些氨基酸（蛋白质的组成单位）转化为通常只存在于肉类中的化合物。

Fan is part of a team that put genetic instructions for making these animalbased enzymes into a bacterium: Agrobacterium tumefaciens. This microbe can then transfer genes to plants.

范鹏祥研究团队将制造这些动物源性酶的基因指令植入了根癌农杆菌。接下来，这种微生物便可将基因转移到植物中。

The team prepared multiple sets of genetic instructions. The sets differ in which amino acids and nutrients they can make.By combining the sets in different wayslike combining Lego blocks to build different structures-the instructions would allow plants to make different nutrients.The researchers then injected bacteria carrying these instructions into the leaves on a relative of the tobacco plant.

研究团队准备了多组基因指令，这几组指令能够合成不同的氨基酸和营养素。通过不同的组合方式——就像用乐高积木搭建不同结构一样——这些指令可以让植物合成不同的营养素。研究人员随后将携带这些指令的细菌注入一种烟草近亲的叶片。

The treated leaves then made two animal-type nutrients. One was creatine.It's a molecule formed from three amino acids. The other, carnosine, is made from two amino acids. In both people and animals, creatine helps bring energy to muscles. Carnosine is an antioxidant.It also helps stave off' muscle fatigue.

经过处理的叶片合成了两种动物源性营养素：一种是肌酸，由三种氨基酸组成；另一种是肌肽，由两种氨基酸组成。在人和动物体内，肌酸有助于为肌肉提供能量，而肌肽是一种抗氧化剂，还能帮助延缓肌肉疲劳。

Which nutrient the leaves made depended on which genetic instructions they had received. After four to five days, the researchers harvested leaves from the plants.

叶片合成出哪种营养素取决于它们接收到的基因指令。四到五天后，研究人员从植物上采集了叶片。

People need about 1.7 grams of creatine and 0.6 gram of carnosine each day. The amounts of creatine and carnosine that the plant made are much less than that, Fan notes.

人体每天需要约1.7克肌酸和0.6克肌肽。范鹏祥指出，植物合成的肌酸和肌肽量远低于此。

For every gram of plant leaf with animal enzymes, the plant had made 2.3 micrograms of creatine or 69.5 micrograms of carnosine. (A microgram is a millionth of a gram. It's about onefiftieth the weight of a grain of salt.) For comparison, a gram of meat contains about 1,000 times as much creatine and about 100 times as much carnosine as a gram of the modified plant.

每克含有动物源性酶的植物叶片可合成2.3微克肌酸或69.5微克肌肽。（1微克是百万分之一克，约为一粒盐重量的五十分之一。）相比之下，每克肉类中的肌酸含量是每克改造植物的约1000倍，肌肽含量则是约100倍。

The team shared its findings in the October 16 Journal of Agricultural and Food Chemistry.

范鹏祥团队的研究成果发表在10月16日的《农业与食品化学杂志》上。

The plants used to test this technique aren't edible. But one day, Fan hopes to try adding such nutrient-making enzymes to crops such as tomatoes.

用于测试改造技术的植物不可食用，但范鹏祥希望未来能将这类营养素合成酶添加到番茄等作物中。

But, Fan cautions, before using this technique in fruits or veggies, "we need to be very careful." The plant might adapt to the genes in unexpected ways.For example, the team tried to get their test plant to make taurine, another nutrient. This amino acid plays a role in digestion. But the injected genes didn't work the way the team had hoped.Those enzymes kept the plant from making cysteine. It's an amino acid the plant needs to make that taurine.

不过，范鹏祥提醒，在将植物改造技术应用于水果或蔬菜之前，“我们需要非常谨慎”。植物可能会以意想不到的方式适应注入体内的基因。例如，研究团队曾尝试让受试植物合成另一种营养素——牛磺酸,这种氨基酸在消化中起重要作用。然而，注入的基因并未产生预期效果，制造出来的酶反倒阻止植物合成半胱氨酸，而半胱氨酸是植物合成牛磺酸所需的氨基酸。

Injecting the genetic instructions into a leaf takes just a few days. That's a lot faster than the typical approach for testing genetic tweaks to plants, says Laurie Leonelli. She's a photosynthesis engineer who did not take part in the study.She works at the University of Illinois Urbana-Champaign. For instance, growing whole plants that carry new genetic instructions can take two or three years.So the new bacteria injections certainly save scientists a lot of time in seeing if their approach works, Leonelli says.

将基因指令注入叶片只需几天的时间。劳丽·莱奥内利表示，这比试验植物基因微调的常规方法快得多。例如，培育携带新基因指令的整株植物可能需要两三年。因此，莱奥内利指出，在验证改造技术是否有效时，新的细菌注射法无疑能为科学家节省大量时间。莱奥内利是一位光合作用工程师，在伊利诺伊大学厄巴纳-香槟分校工作，她未参与范鹏祥团队的研究。

Fan plans to try adding genes for making other animal nutrients to plants,too. Ideally, he says, his group could come up with a set of instructions for every amino acid. People get some other nutrients primarily from meat,too-such as vitamin B12. Fan plans to explore ways to boost plant levels of these nutrients as well.

范鹏祥计划尝试将制造其他动物源性营养素的基因添加到植物中。他表示，理想情况下，他们团队可以为每种氨基酸设计一套指令。人们主要从肉类中获取的还有其他一些营养素，如维生素B2。此外，范鹏祥还计划探索提高植物中这些营养素水平的方法。

If plants are grown in a mindful way, they should have fewer impacts on the environment than the farming of animals have, Leonelli says. The new work is "trying to make plants more nutritious so we don't have to rely so heavily on animal [products]."

莱奥内利表示，如果精心种植，植物对环境的影响应该比畜牧业小。范鹏祥团队的新方法“试图让植物更有营养，从而减轻我们对动物（产品）的严重依赖”。