圖1. 此些於美國布魯克海文國家實驗室，美國二號國家同步加速器光源(NSLS-II：National Synchrotron Light Source II)產生的X-射線"圖像"顯示了，於未改變之植物(左，野生型(WT))及突變之植物(右，opt3)，整個成熟葉柄中，鐵(上列)及銅(下列)的分佈。暖色(紅色、橙色及黃色)顯示高濃度，而冷色(綠色及藍色)顯示低濃度。Xy指向木質部，Ph指向韌皮部，FC指向另一種植物組織─維管束形成層。此些圖像顯示了，突變植物在木質部展現，較高濃度的鐵。令人訝異的是，銅分佈類似鐵分佈。
These x-ray "maps" generated at NSLS-II show the distributions of iron (top row) and copper (bottom row) throughout mature leaf petioles, both in unaltered plants (left, WT) and mutant plants (right, opt3). Warm colors (red, orange, and yellow) indicate high concentrations, and cool colors (green and blue) indicate low concentrations. Xy points to the xylem, Ph points to the phloem, and FC points to the fascicular cambium, another type of plant tissue. The maps showed that the mutant plants exhibited larger concentrations of iron in the xylem and, surprisingly, that the copper distribution resembled the iron distribution.
A team of scientists from Cornell University and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have revealed an unexpected function of a transport protein and its role in plant regulatory mechanisms.
一支來自美國康乃爾大學及美國能源部(DOE)所屬布魯克海文國家實驗室的科學家團隊業已揭露，一項輸送蛋白質之意想不到的功能，及其在植物調節機制中的角色。
Their research, published in The Plant Cell earlier this year, could help reduce human mineral deficiencies by packing essential micronutrients into edible parts of plants.
Iron is an essential mineral for humans.
今年(2023年)稍早，他們發表於《植物細胞》期刊的研究，可能有助於人類，藉由將必需的微量營養素，集中到植物可食部分中，來減少人類必需之鐵礦物質的缺乏。
In addition to being a key component of hemoglobin—the red blood cell protein that carries oxygen throughout the body—iron aids the immune system and plays a role in cognitive functions. The human body cannot produce iron, so it must be consumed regularly.
除了是血紅蛋白(將氧氣輸送到全身的紅血球蛋白質)的關鍵成分之外，鐵有助於免疫系統，且在認知功能中扮演一種角色。人體不能產生鐵，因此必須經常食用。
Plants, like spinach, are one source of iron, but their strict regulatory mechanisms prevent minerals from over accumulating because they are toxic to the plant in high concentrations. Scientists, however, have been studying the transport of minerals, like iron, to figure out a way to override these regulatory mechanisms and increase the nutritional value of edible plants.
植物(諸如菠菜)是鐵的來源之一。不過，其嚴密的調節機制，防止了礦物質過度累積。因為，在高濃度下，它們對植物有毒。不管怎樣，科學家們一直在研究，礦物質(諸如鐵)的輸送，以找到一種方法，來超越此些調節機制，及提高可食用植物的營養價值。
圖2. 如同那些於該項研究中使用的植物，於研究中，擬南芥植物經常被使用。因為，它們繁殖迅速，且具有完整被描繪出的較短基因體。
Arabidopsis thaliana plants, like those used in this study, are often used in research because they reproduce quickly and have a short genome that is entirely mapped out.
“This story started long ago,” explained Olena Vatamaniuk, a plant biologist from Cornell and head of the lab responsible for this research. Nearly a decade ago, Vatamaniuk and her colleagues published a surprising discovery—a transport protein called oligopeptide transporter 3 (OPT3) is responsible for moving iron within a model plant called Arabidopsis thaliana, rather than the oligopeptides (small peptides) that the transporter was named for.
康乃爾大學植物生物學家，兼負責這項研究的實驗室領導人，Olena Vatamaniuk解釋：「此研究的由來，開始於很久以前。」 近十年前，Vatamaniuk 及其同僚們，發表了一項令人訝異的發現。一種被稱為寡肽輸送物3 (OPT3)的輸送蛋白質，在被稱為擬南芥(Arabidopsis thaliana)的模型植物中，負責運送鐵。而不是被命名為輸送物的寡肽(小肽)。
As part of an earlier study, researchers at the University of Missouri had found that decreasing OPT3 altered the distribution of iron throughout the A. thaliana plant; the roots were showing signs of iron deficiency, despite an abundance of iron in the leaves.
作為一項較早期研究的一部分，美國密蘇里大學的研究人員們發現，減少OPT3改變了，整個擬南芥植物中，鐵的分佈。儘管，於葉子中，有豐富的鐵。不過，根部展現缺鐵的跡象。
This indicated that OPT3’s role was related to the communication of iron status from the leaves, known as the shoot, to the roots. The two findings were just the start of a complicated story.
這顯示了，OPT3的角色與鐵狀態，從被通稱為新芽的葉子到根部的交流有關。這兩項發現，只是一項複雜研究由來的開端。
“In our latest study, we wanted to use our knowledge of OPT3’s role to figure out how the transporter was related to shoot-to-root signaling,” said Vatamaniuk. Taking a look inside the plants with ultrabright x-rays was the first step—but OPT3 had another surprise in store for the scientists.
Vatamaniuk宣稱：「在我們最近的研究中，我們想利用咱們有關OPT3角色的知識，來瞭解此輸送物如何，與新芽到根部的發信號有關。第一步是使用超亮的X-射線，來透視植物內部。不過，對此些科學家而言，OPT3具有必將發生的另一驚喜。」
When scientists want to figure out what a protein does, they often choose to observe what doesn’t happen when most, if not all, of the protein is removed from a sample. Removing all OPT3 protein would be lethal to the plant species used in this study, so the researchers genetically altered the plants, creating “mutants” with a lower abundance of OPT3 transporters.
當科學家們想瞭解蛋白質的作用時，他們通常會選擇觀察，當大部分(倘若不是全部)蛋白質，從樣本中被移除時，不會發生什麼。移除所有OPT3蛋白質，對在該項研究中，使用的植物物種，會是致命的。因而，此些研究人員遺傳改變這些植物，創造了具較低OPT3輸送物豐度的“突變體”。
Vatamaniuk and her colleagues wanted to look at how the iron distribution throughout the vascular system differed between the mutant and unaltered plants. The researchers were particularly interested in a transport tissue, called the phloem, because they had discovered OPT3 moving iron into this tissue nearly a decade earlier.
Vatamaniuk及其同僚們想探究，在此些突變與未經改變之植物間，鐵在整個維管束系統中的分佈，為何有差異。此些研究人員特別感興趣於一種，被稱為韌皮部的輸送組織。因為，近十年前，他們已經發現，OPT3將鐵移動到該組織中。
The phloem typically transports nutrients from areas where they are highly concentrated, known as sources, to areas where they are scarce, known as sinks. This contrasts the xylem vascular tissue, which transports water and nutrients from the roots to the shoot.
通常，韌皮部將營養物質，從被通稱為源之營養物質高度集中的區域，被輸送到被通稱為匯之營養物質缺乏的區域。這與將水分及養分，從根部輸送到新芽的木質部維管束組織，形成對比。
One way to analyze iron distributions in tissues and cells is with confocal x-ray fluorescence imaging (C-XRF), a technique recently developed by Cornell beamline scientist Arthur Woll. Like conventional x-ray fluorescence (XRF) imaging, this technique uses bright x-ray light to reveal the locations of different chemical elements within a sample.
分析鐵在組織及細胞中分佈的一種方法，是使用最近由美國康乃爾大學，光束線科學家Arthur Woll所開發，共焦X-射線螢光造影(C-XRF)技術。如同傳統X-射線螢光(XRF)造影，該項技術使用明亮的X-射線，來揭露樣本中，不同化學元素的所在處。
But the addition of a very tiny, special lens designed by Woll, called a confocal optic, provides depth sensitivity for researchers to quantify the elemental concentrations within specific compartments of thick samples. Researchers at Cornell create these lenses through a process called nanofabrication.
不過添加了一種由Woll所設計，被稱為共焦光學部件之非常微小的特殊透鏡，為研究人員們提供了深度靈敏度，來量化厚樣本特定部分內的元素濃度。
To apply this technique at an ultra-small scale, the Cornell scientists brought their sample to one of the most advanced x-ray light sources in the world, the National Synchrotron Light Source II (NSLS-II). NSLS-II is a DOE Office of Science User Facility at Brookhaven Lab that produces light beams 10 billion times brighter than the sun.
為了以超小規模應用這項技術，康乃爾大學的科學家們，將其樣本帶到世界上最先進的X-射線光源之一，美國二號國家同步加速器光源(NSLS-II)。NSLS-II是美國能源部科學局，位於布魯克海文實驗室，產生比太陽更明亮，1百億倍光束的用戶設施。
“NSLS-II was the only facility with a bright enough beamline to get us the resolution that we wanted,” explained Ju-Chen Chia, a researcher in Vatamaniuk’s lab and lead author of this paper. “At the time, no other facility could get us the single-micron resolution C-XRF images that we needed.”
屬Vatamaniuk實驗室研究員，兼該項論文的首要撰文人，Ju-Chen Chia解釋：「NSLS-II是唯一，具有足夠明亮光束線，來使我們獲得想要之解析度的設施。那時，沒有其他設施能使我們獲得，需要之單微米解析度的C-XRF影像。」
圖3. 上圖示，在NSLS-II亞微米解析度X-射線光譜學(SRX)光束線下，科學家們將一道超亮光束，聚焦於一平方微米上。此光照亮了一段葉柄，因此科學家們能視覺化，化學元素於整個植物脈管系統中的分佈。
At the NSLS-II Submicron Resolution X-ray Spectroscopy (SRX) beamline, shown above, scientists focused a ultrabright light beam down to a single square micron. This light illuminated a section of a petiole so the scientists could visualize the distribution of chemical elements throughout the plant vasculature.
The research team’s first stop at NSLS-II was the Submicron Resolution X-ray Spectroscopy (SRX) beamline, led by Andrew Kiss. Woll and Kiss situated a series of mirrors to focus the x-ray beam down to a single square micron on a section of a petiole—the part of the plant connecting the leaves to the stem.
該研究團隊於NSLS-II的第一站，是由Andrew Kiss領導的亞微米解析度X-射線光譜學(SRX)光束線。Woll及Kiss放置了一系列鏡子，將X-射線束聚焦到，植物連接葉子到莖部的部分葉柄上。
The interactions between the x-ray beam and the leaf petiole emitted fluorescent x-ray signals, which propagated through a nanofabricated confocal optic located only one millimeter away before they were recorded by a silicon drift detector.
X-射線束與葉柄間的交互作用發出了，在被矽漂移探測器記錄之前，透過一種被安置於僅一毫米外，奈米製造之共焦光學元件，傳播的螢光X-射線訊號。
“This was really challenging from a technical perspective,” noted Kiss. In addition to working with a small beam spot size, the researchers also had to ensure x-rays from only the surface of the leaf petiole were collected. X-rays collected from the depth of the sample would reduce the resolution and effectively blur the image.
Kiss特別提及：「從技術觀點，這確實具挑戰性。」除了使用小光束點的尺寸，來進行研究外，此些研究人員也必須確保收集，僅來自葉柄表面的X-射線。收集自樣本深處的X-射線，會降低解析度而顯著模糊影像。
The x-ray fluorescence contains characteristic energies that are like fingerprints for each element in the sample. Kiss and the Cornell scientists decoded these x-rays to figure out which elements were in the sample, the concentrations of those elements, and precisely where they were located.
這種X-射線螢光具有像是樣本中，每一元素指紋的獨特能量。Kiss及康乃爾大學的科學家們，解碼了此些X-射線，以瞭解樣本中是哪些元素、那些元素的濃度及其精確位置。
“In the original paper, we proposed that OPT3 is important for loading iron into the phloem,” explained Chia. “So, we thought that if we analyzed the mutant plant vascular tissues using C-XRF, we should see more iron in the xylem but less iron in the phloem of the mutant.”
Chia解釋：「在原始論文中，我們提出了，OPT3對於將鐵裝載到韌皮部的重要性。因此，我們認為，倘若使用C-XRF分析了，突變之植物維管束組織。在突變的木質部中，我們應該看到更多的鐵，不過在韌皮部中，看到較少的鐵。」
The researchers found exactly what they were looking for—but their subsequent analyses took them by surprise.
此些研究人員精確發現了，他們找尋的東西。不過，隨後的分析令他們驚訝。
Some transport proteins move more than one molecule; in plants, iron is often transported with zinc or manganese. So, analyzing the distributions of multiple minerals, in addition to the mineral of interest, is a fairly common practice when conducting x-ray fluorescence experiments.
有些輸送蛋白質移動多於一個分子；在植物中，鐵經常與鋅或錳一起被輸送。因此，當進行X-射線螢光實驗時，除了感興趣的礦物質之外，分析多種礦物質的分佈，是相當普遍的做法。
“Sometimes changing the concentration of one mineral causes a bunch of other concentration changes in plants,” explained Chia. “Iron, copper, zinc, and manganese are all essential minerals for plant growth, so we like to look at all of them at the same time.”
Chia解釋：「有時，改變一種礦物質濃度，導致植物中，一系列其他濃度的變化。鐵、銅、鋅、錳，皆是植物生長不可或缺的。因此，我們想要同時探究，所有此些礦物質。」
Though it is essential, copper does not typically share transporters with other minerals in plants. That’s why the researchers were especially shocked when they observed changes in the mutant plant’s copper distribution that mimicked those of the mutant’s iron distribution—indicating that OPT3 also transported copper into the phloem.
雖然銅極為重要，不過通常它不會與植物中，其他礦物質共享輸送蛋白質。那是為何當此些研究人員觀察到，突變植物銅分佈中的變化，與突變植物鐵分佈酷似時，他們感到特別震驚。顯示，OPT3也將銅輸送至韌皮部中。
“If we hadn’t brought our samples to NSLS-II, we never would have considered one transporter moving both iron and copper in a plant,” said Vatamaniuk, emphasizing how unexpected these results were. “It is quite unusual.”
強調此些研究結果是多麼意想不到的Vatamaniuk宣稱：「倘若沒將樣本帶往NSLS-II，我們永遠不會料想到，於植物中，一種輸送蛋白質移動鐵及銅兩者。這十分不尋常。」
“This work was a great technical accomplishment for the SRX beamline,” noted Kiss. “But it was an even greater demonstration of the expertise and collaboration here at NSLS-II.” Throughout these experiments, Kiss and Woll worked with Ryan Tappero, leader of the X-ray Fluorescence Microscopy (XFM) beamline, where Chia and her colleagues conducted complementary experiments to confirm their findings.
Kiss特別提及：「該項研究是SRX光束線的一大技術成就。除外，這是在NSLS-II這裡之專業知識及合作，一項更引人矚目的示範。」在這些實驗中，Kiss及Woll與X射線螢光顯微鏡學(XFM)光束線的領導人Ryan Tappero進行了研究合作。在此Chia及其同僚們進行了補充實驗，以證實他們的研究發現。」
At the XFM beamline, the Cornell scientists wanted to visualize the internal distribution of elements throughout the vasculature of embryonic plants, which were contained within mature seeds.
以XFM光束線，康乃爾大學的科學家們想視覺化，整個胚胎植物脈管系統，在成熟種子中，具有之元素的內部分佈。
Though cutting open the seeds and scanning their surface—like how the scientists studied the leaf petiole with C-XRF—was tempting, cutting the seeds open could cause element redistribution. Exposing the delicate structures to oxygen could also lead to chemical reactions that change their elemental makeup.
雖然切開種子並掃描其表面，如同此些科學家如何使用C-XRF研究葉柄，是引人感興趣的，不過切開種子可能導致元素重新分布。將此些脆弱的結構物曝露於氧中，也可能導致改變其元素組成的化學反應。
圖4. 上圖示，研究人員們使用了，於NSLS-II X-射線螢光顯微鏡學(XFM)光束線下，記錄的螢光訊號，無需切開此些種子，來獲得植物種子的橫斷面影像。
Researchers used fluorescence signals recorded at the NSLS-II X-ray Fluorescence Microscopy (XFM) beamline, shown above, to derive cross-sectional images of plant seeds without cutting the seeds open.
“Just like medical doctors take CT scans of your body without cutting you open, we used x-rays at the XFM beamline to take a ‘chemical’ CT scan of the mineral elements inside the seeds without cutting them open,” Tappero explained.
Tappero解釋：「就如同醫生們，在沒切開人體下，進行電腦斷層掃描(CT：computed tomography)。我們使用了，以XFM光束線的X-射線，來在沒切開種子下，進行其內部礦物元素的‘化學’電腦斷層掃描。」
Medical CT scans rely on a rotating x-ray source and detector to take a series of exposures, from which computers can reconstruct cross-sectional images of internal structures. NSLS-II scientists do not rotate the x-ray beam, so instead they programmed instrumentation to rotate the seed samples in the x-ray beam while recording the x-ray fluorescence signals.
醫療的電腦斷層掃描，仰賴一種旋轉的X-射線源及偵測器，來進行一系列曝光。從這些電腦能重建內部結構物的橫截面影像。NSLS-II的科學家們並不旋轉此X-射線束，因此他們轉而為憑藉儀器的操作設計了程式，來旋轉於X-射線束中的種子樣本，同時記錄X-射線螢光訊號。
“The seeds were only half a millimeter in diameter, which made them ideal to scan intact,” Tappero explained. As each egg-shaped seed was zapped with ultrabright x-rays, fluorescence signals could radiate out from the center of the seeds to be measured by a silicon drift detector.
Tappero解釋：「此些種子直徑僅半毫米，這使其是完整掃描的理想物。」當每一蛋形種子被以超明亮X-射線照射時，螢光訊號會從種子中心輻射出，來由一種矽漂移探測器進行測量。
After the first exposure, instrumentation rotated the sample by less than one degree so it could be zapped again from another angle. The instrumentation automatically repeated this process until the sample was rotated a full 360 degrees. This technique is called x-ray fluorescence computed microtomography (F-CMT).
於首次曝光後，儀器旋轉了此種樣本不到一度。因此，能從另一個角度，再度被照射。憑藉儀器的操作自動重複此過程，直到樣本旋轉完整360 度。此種技術，被稱為X-射線螢光電腦顯微斷層掃描(F-CMT)。
F-CMT cross-sectional images are derived from fluorescence signals like conventional XRF images; however, scientists use additional computer reconstruction techniques to provide the cross-sectional views.
F-CMT橫截面影像源自，類似傳統XRF影像的螢光訊號；不過，科學家使用了額外的電腦重建技術，來提供橫截面視圖。
Using these cross-sectional images to visualize the internal distribution of elements in the embryonic plants, the scientists observed lower concentrations of both iron and copper in the vascular cells of the mutant seeds compared to the unaltered seeds. These results served as further evidence of the OPT3 transporter moving both iron and copper.
利用此些橫截面影像來視覺化，於胚胎植物中，元素的內部分佈。此些科學家觀察到，鐵及銅兩者，於突變種子維管束細胞中，與未改變之種子相較下，較低的濃度。此些研究結果充當了，OPT3輸送蛋白質，同時移動鐵及銅的進一步證據。
“We brought our samples to NSLS-II so we could observe the physiology of this transport protein and we got to come back to our lab with an important piece of the puzzle that lies at the center of it all,” noted Chia. “Everything was about to come together.”
Chia特別提及：「我們將樣本帶到NSLS-II，以便我們能觀察此輸送質蛋白的生理機能。然後，我們能帶著，完全位於其核心之謎團的重要部分，回到我們的實驗室。一切即將到齊。」
The researchers returned to their Cornell labs to make sense of their new findings with a deep dive into the mutant plant’s genetics. Through a series of experiments, they discovered that iron and copper not only share a transport protein, but they also interact in a complex signaling pathway that regulates their uptake through gene expression.
此些研究人員返回了，他們於康乃爾大學的實驗室，以深入研究此突變植物的遺傳現象，來理解他們的此些新發現。透過一系列實驗，他們發現了，鐵及銅不僅共享一種輸送蛋白質，而且也在透過基因表現，來調節其吸收的複雜發信號途徑中，交互作用。
This research is just one step towards mitigating human mineral deficiencies by changing the nutrient content of edible plants. Vatamaniuk and her colleagues studied A. thaliana, a non-grass plant that is often used in research because it reproduces quickly and has a short genome that is entirely mapped out.
該項研究只是藉由改變食用植物的營養成分，來朝向減輕人類礦物質缺乏的一步。Vatamaniuk及其同僚們研究了擬南芥，這是一種常被用於研究的非草本植物。因為，它快速繁殖，且具有完全被繪製出的短基因體。
The researchers can now use their findings to look at the function of this transport protein in grass plants like rice, wheat, or barley. “The physiology of a plant can tweak the function of a transporter,” explained Vatamaniuk. “So, it is important to apply this knowledge to other plants. I’m sure there are more discoveries to come.”
目前，此些研究人員能利用他們的這些研究發現，來探究此種輸送蛋白質，在類似稻米、小麥或大麥等，草本植物中的功能。Vatamaniuk解釋：「植物的生理機能，能調整輸送蛋白質的功能。因此，將此知識應用於其他植物，這很重要。我確信會有更多的發現。」
“I want to express gratitude to the NSLS-II scientists because they really help us,” she added. “The nature of collaboration is so important, but they are also just so friendly and helpful.”
“We have so many ambitious ideas,” Chia said, “and they help us bring them to life.”
她附言：「我想對NSLS-II的科學家們，表達感謝。因為，他們很幫助我們。合作的本質非常重要，然而他們也實在很友好且給予幫助。」Chia宣稱：「我們有很多雄心勃勃的構想，而他們幫助我們使之實現。」
網址：https://www.bnl.gov/newsroom/news.php?a=221431
翻譯：許東榮
文章定位：
