玫瑰是红色的,紫罗兰是蓝色的,是什么让花朵有了夺目的色彩?

2017-02-14 10:59:20 来源: 中国科技网 作者: 张微编译

为了揭开花朵颜色的谜团,为什么玫瑰是红色的,紫罗兰是蓝色?科学家们正在研究植物花瓣的基因。

科罗拉多大学博尔德分校的进化生物学家斯泰西 史密斯说:“当你问一个人一朵花与另一朵花有什么区别的时候,对于我们大多数人来说,第一个想到的差别是颜色。”

很多人都不会考虑这个问题:为什么每种花都有特定的颜色,但是这个问题对于生物学家却很重要,美国国家科学基金会(NSF)环境生物学部(他们资助了史密斯的研究项目)的项目主任Prosanta Chakrabarty说。

史密斯和她的研究团队正在“研究花朵颜色遗传学,以及随着时间的推移,这些颜色的变化,” Chakrabarty说。

在大自然中,花朵是五颜六色,万紫千红的。

“在微观层面上,颜色来自花瓣细胞的生化成分,”史米斯说。

色素是赋予花朵颜色的主要化学物质。植物中含有的色素化合物数以千计,可以分为三大类:黄酮类、类胡萝卜素、甜菜碱。大多数花的颜色来自类黄酮和类胡萝卜素。

除了赋予花朵颜色之外,类胡萝卜素和花青素(黄酮类化合物)还具有抗氧化和其它药用价值,包括抗癌、抗菌、抗真菌和抗炎活性,”美国国家科学基金会环境生物学部的一个项目主任Simon Malcomber说。

Malcomber说,研究表明植物如何进化合成类胡萝卜素和花青素从而产生红色的花。”这些结果可以用于今后的药物发现研究,“他说。

史密斯的大部分工作都集中在了解类黄酮和类胡萝卜素生物化学特性如何发生与花朵颜色差异相关的变化。她和同事对番茄家族(大约2800个物种)进行研究,包括番茄、茄子、辣椒、烟草和马铃薯。

“这些栽培型物种的花朵颜色并不丰富,但是它们的野生近缘种却不是如此”史密斯说。“因此我们研究野生近缘种或非栽培型物种”,它们在南美洲分布广泛。

史密斯分享了她在野外的冒险经历,比如她在厄瓜多尔火山坑的底部寻找一种红色花朵的植物。

史密斯说:“这是我第一次实地考察,我不是超级聪明的人。”我乘车到火山口外,把我的手提箱拖到火山边缘,然后进入火山口,我以为这下面有村庄和能走出去的路。实际上什么也没有。谢天谢地,附近有一个住宿点,我可以在那里过夜。第二天我在森林里发现开满鲜花的物种。

史密斯目前正在寻找问题的答案:红色花朵首次出现在番茄家族是什么时候?“我们认为红色花朵彼此独立地进化了很多次,因为红色物种散落在这个家族族谱的很多分支中,”她说。

然而,在整个番茄家族中只有34种有红色花朵。

“因为数量少,我们可以对每个物种进行采样,以研究它是否代表一个独立的起源,并确定红色花朵的生物化学特性,”史密斯说。

她和其他生物学家从巴西到了哥伦比亚和墨西哥,追踪红色花朵并研究它们的色素。“我们发现了一个令人惊讶的模式”史密斯说,“包括几乎每个红色花朵物种都代表一种颜色的新起源,因此红色花朵至少进行了30次。”

虽然研究人员预计,由于红色色素的存在,花朵会变红,但他们发现植物通常将黄橙色类胡萝卜素和紫色花青素结合在一起,产生红色花朵。

史密斯说:“我们的研究旨在追踪植物产生花朵颜色的整个遗传路径,并识别基因的变化,了解它们是否有共同的机制.”。

例如,科学家们想知道,自从花朵首次变成红色后,接下来发生了什么变化?

“我们正在研究番茄家族[牵牛花]的一个分支,创建进化历史并检测基因表达,色素的产生和花的颜色,”史密斯说。

史密斯说,在本研究中,牵牛花和它们色彩丰富的近缘物种是不错的选择。

“我们中的很多人都在苗圃中见到过牵牛花颜色的千变万化,事实上,科学家将牵牛花作为研究对象,研究花的颜色和生化特性已经有几十年的历史了。”

很少有人知道牵牛花野生近缘的变化,它们中的大部分是在阿根廷和巴西被发现的。“我们利用自然的多样性,以及从观赏性牵牛花身上获取的遗传信息,重构了花朵颜色的进化历史,”史密斯说。

“如果之前的研究让我们得出了某些结论,”她补充道,“我们就不应该指望花朵能够按部就班进化。”

玫瑰会永远是红色的,紫罗兰会永远是蓝色的吗?(张微编译)

以下为英文原文:

Roses are red, violets are blue—what gives flowers those eye-catching hues?

To solve the mystery of why roses are red and violets are blue, scientists are peering into the genes of plant petals.

"When you ask anyone how one flower is different from another, for most of us, color is the feature that first comes to mind," says evolutionary biologist Stacey Smith of the University of Colorado Boulder.

Most people don't think about why a flower is a particular color, but it's an important question for biologists, says Prosanta Chakrabarty, a program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funds Smith's research.

Smith and her team are "looking at the genetics of flower colors, and at changes in those colors over time," Chakrabarty says.

It all comes down to biochemistry

In nature, flowers come in hues that span the rainbow.

"On a microscopic level, the colors come from the biochemical composition of petal cells," Smith says.

Pigments are the main chemicals responsible. Plants contain thousands of pigment compounds, all of which belong to three major groups: flavonoids, carotenoids and betalains. Most flower colors come from flavonoids and carotenoids.

"In addition to giving flowers their colors, carotenoids and anthocyanins—which are flavonoids—have antioxidant and other medicinal properties, including anti-cancer, antibacterial, antifungal and anti-inflammatory activity," says Simon Malcomber, a program director in NSF's Division of Environmental Biology.

Malcomber says the research could show how plants evolved to synthesize the carotenoids and anthocyanins that produce red flowers. "The results could be used in future drug discovery research," he says.

Much of Smith's work is focused on understanding how changes in flavonoid and carotenoid biochemistry relate to differences in flower colors. She and colleagues conduct research on the tomato family, a group of about 2,800 species that includes tomatoes, eggplants, chili peppers, tobacco and potatoes.

"These domesticated species don't have a terribly wide range of flower colors and patterns, but their wild relatives often do," Smith says. "So we study wild, or undomesticated, species, which are most diverse in South America."

Hot pursuit of red-hot color

Smith has had her share of adventures in the field—like the time she tried to find a plant with red flowers that lives at the base of a volcanic crater in Ecuador.

"It was my very first field trip, and I wasn't super-savvy," Smith says. "I took a bus to the outside of the crater, dragged my suitcase up to the rim then down into the crater, assuming there would be a village and a way to get out. There was neither. Thankfully, there was a park station nearby where I was able to stay overnight. I found the species in full flower in the forest the next day."

Smith is currently in hot pursuit of an answer to the question: When did red flowers first appear in the tomato family? "We thought that red flowers might have evolved many times independently of each other because red-flowered species are scattered among many branches of this family tree," she says.

Just 34 species in the entire tomato family, however, have red flowers.

"With such a small number, we can take samples of every one of these species to find out whether it represents an independent origin, and to determine the biochemistry of how it makes red flowers," Smith says.

She and other biologists traveled from Brazil to Colombia to Mexico to track down red flowers and measure their pigments. "We found surprising patterns," Smith says, "including that nearly every red-flowered species represents a new origin of the color, so red flowers have evolved at least 30 different times."

While the researchers expected that flowers would be red due to the presence of red pigments, they found that plants often combine yellow-orange carotenoids with purple anthocyanins to produce red flowers.

"Our studies are now aimed at tracing the entire genetic pathway by which plants make flower colors and identifying genetic changes to see if there are common mechanisms," Smith says.

The scientists want to know, for example, what changes have taken place since flowers first became red.

Answers in a petunia

"We're focusing on a single branch of the tomato family [petunias], creating an evolutionary history and conducting measurements of gene expression, pigment production and flower color," says Smith.

Petunias and their colorful relatives are good choices for this research, according to Smith.

"Most of us have seen the tremendous variation in petunia colors at our local nurseries, and indeed, petunias have served as models for studying flower color and biochemistry for decades."

Few people, though, are aware of the variation in petunias' wild relatives, most of which are found in Argentina and Brazil. "We're harnessing this natural diversity, as well as genetic information already available from ornamental petunias, to reconstruct the evolutionary history of flower colors," says Smith.

"If earlier studies taught us anything," she adds, "we shouldn't expect flowers to play by the rules."

Will roses always be red, and violets blue?

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