Microbes Give Plants a Way to Make ‘Meaty’ Nutrients微生物助力植物合成“肉類”營養(yǎng)素

The approach could help vegetarians get all the nutrients they need in new ways.

這一方法可以幫助素食者通過新途徑獲取所需的所有營養(yǎng)。

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 tweaked1 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.

蔬菜富含多種營養(yǎng)，但人體所需的某些營養(yǎng)素只能從肉類、牛奶等動物產(chǎn)品中獲取。如今，研究人員通過微調(diào)植物葉片的基因，使植物最終也能合成部分動物源性營養(yǎng)素。未來，素食主義者和純素食者或許可以依靠植物獲取身體所需的全部營養(yǎng)。

“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.

“我媽媽是素食主義者，”范鵬祥說，“所以我開始研究如何改善植物性飲食。”范鵬祥是一位生物化學(xué)家，在中國杭州的浙江大學(xué)工作。

Enzymes are proteins that speed up chemical reactions inside living things. To pump out2 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 proteins—into compounds normally found only in meat.

酶是能夠加速生物體內(nèi)化學(xué)反應(yīng)的蛋白質(zhì)。為了合成動物源性營養(yǎng)素，植物葉片需要它們通常不具備的酶。具體來說，它們所需的那類酶能夠?qū)⒛承┌被幔ǖ鞍踪|(zhì)的組成單位）轉(zhuǎn)化為通常只存在于肉類中的化合物。

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

范鵬祥研究團(tuán)隊將制造這些動物源性酶的基因指令植入了根癌農(nóng)桿菌。接下來，這種微生物便可將基因轉(zhuǎn)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 ways—like 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.

研究團(tuán)隊準(zhǔn)備了多組基因指令，這幾組指令能夠合成不同的氨基酸和營養(yǎng)素。通過不同的組合方式——就像用樂高積木搭建不同結(jié)構(gòu)一樣——這些指令可以讓植物合成不同的營養(yǎng)素。研究人員隨后將攜帶這些指令的細(xì)菌注入一種煙草近親的葉片。

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 off3 muscle fatigue.

經(jīng)過處理的葉片合成了兩種動物源性營養(yǎng)素：一種是肌酸，由三種氨基酸組成；另一種是肌肽，由兩種氨基酸組成。在人和動物體內(nèi)，肌酸有助于為肌肉提供能量，而肌肽是一種抗氧化劑，還能幫助延緩肌肉疲勞。

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.

葉片合成出哪種營養(yǎng)素取決于它們接收到的基因指令。四到五天后，研究人員從植物上采集了葉片。

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.

人體每天需要約1.7克肌酸和0.6克肌肽。范鵬祥指出，植物合成的肌酸和肌肽量遠(yuǎn)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 one-fiftieth 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.

每克含有動物源性酶的植物葉片可合成2.3微克肌酸或69.5微克肌肽。（1微克是百萬分之一克，約為一粒鹽重量的五十分之一。）相比之下，每克肉類中的肌酸含量是每克改造植物的約1000倍，肌肽含量則是約100倍。

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

范鵬祥團(tuán)隊的研究成果發(fā)表在10月16日的《農(nóng)業(yè)與食品化學(xué)雜志》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.

用于測試改造技術(shù)的植物不可食用，但范鵬祥希望未來能將這類營養(yǎng)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.

不過，范鵬祥提醒，在將植物改造技術(shù)應(yīng)用于水果或蔬菜之前，“我們需要非常謹(jǐn)慎”。植物可能會以意想不到的方式適應(yīng)注入體內(nèi)的基因。例如，研究團(tuán)隊曾嘗試讓受試植物合成另一種營養(yǎng)素——牛磺酸，這種氨基酸在消化中起重要作用。然而，注入的基因并未產(chǎn)生預(yù)期效果，制造出來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.

將基因指令注入葉片只需幾天的時間。勞麗·萊奧內(nèi)利表示，這比試驗植物基因微調(diào)的常規(guī)方法快得多。例如，培育攜帶新基因指令的整株植物可能需要兩三年。因此，萊奧內(nèi)利指出，在驗證改造技術(shù)是否有效時，新的細(xì)菌注射法無疑能為科學(xué)家節(jié)省大量時間。萊奧內(nèi)利是一位光合作用工程師，在伊利諾伊大學(xué)厄巴納-香檳分校工作，她未參與范鵬祥團(tuán)隊的研究。

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.

范鵬祥計劃嘗試將制造其他動物源性營養(yǎng)素的基因添加到植物中。他表示，理想情況下，他們團(tuán)隊可以為每種氨基酸設(shè)計一套指令。人們主要從肉類中獲取的還有其他一些營養(yǎng)素，如維生素B12。此外，范鵬祥還計劃探索提高植物中這些營養(yǎng)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].”

萊奧內(nèi)利表示，如果精心種植，植物對環(huán)境的影響應(yīng)該比畜牧業(yè)小。范鵬祥團(tuán)隊的新方法“試圖讓植物更有營養(yǎng)，從而減輕我們對動物（產(chǎn)品）的嚴(yán)重依賴”。

1 tweak稍稍改進(jìn)。

2 pump out不斷地大量生產(chǎn)。" 3 stave off延緩。