There have been numerous experiments into plant growth in space. It's important to scientists on the ground because it can help us better understand how plants function which can help us to grow food more efficaciously. It's also important to NASA, because when we finally start sending astronauts away from low Earth orbit, they may need to grow their own food and maintain their own regenerable atmosphere.
人們已經(jīng)做了許許多多關(guān)于植物在太空生長(zhǎng)的實(shí)驗(yàn)，因?yàn)檫@些實(shí)驗(yàn)幫助那些在地表科學(xué)家們更好了解植物的運(yùn)作方式以幫助我們更有效的生產(chǎn)事物，對(duì)于美國(guó)航天航空局（NASA）來(lái)說(shuō)了解這些同樣重要，因?yàn)楫?dāng)我們開(kāi)始將航天員送往低地球軌道，他們就有必要種植自己的植物以及維持空氣的可再生。
Gravity is not the only difference between the Earth environment and the ISS environment. In the closed atmosphere of a spacecraft, volatile organic compounds (VOCs) can accumulate. VOCs need to be scrubbed from the air or seed production will suffer. There are elevated radiation levels that can cause mutations and affect growth. An experiment on Mir, that involved storing tomato seeds in space for six years found mutation rates up to 20 times higher in the space seeds than in the control seeds stored on the ground. And there are the spectral effects of using only electric lighting.
相比地表與國(guó)際空間站（ISS）的環(huán)境來(lái)說(shuō)重力不是唯一不同的因素，在封閉宇宙飛船大氣中，可揮發(fā)的有機(jī)物質(zhì)（VOCs）可以積累下來(lái)，而這些物質(zhì)必須將其從大氣或者種子產(chǎn)物中去除（控制變量），同時(shí)宇宙環(huán)境中有過(guò)量的射線可以導(dǎo)致植物的變異以及影響植物的生長(zhǎng)，Mir做了一個(gè)實(shí)驗(yàn)，它將土豆的種子分別貯藏在太空與地表六年發(fā)現(xiàn)太空種子的突變率是地表的20倍或更高，這里還有一個(gè)關(guān)于光譜的影響太空中因?yàn)橹皇褂昧穗姎庹彰鳌?/strong>
Because plants also respire, we have to have fans to circulate the air around the plants so that they don't suffocate on their own exhalations. Even failed experiments can provide us with better understanding. An experiment to study plant lignin failed to produce healthy plant materials but taught us more about providing effective air movement.
**因?yàn)橹参镌跓o(wú)時(shí)無(wú)刻保持著呼吸，所以在ISS中我們不得不安置了一臺(tái)風(fēng)扇以使的周圍的空氣流通是植物免于被自己的呼出的氣體弄窒息，即便是失敗的實(shí)驗(yàn)也能夠幫助我們更好的理解科學(xué)，一個(gè)研究木質(zhì)素（lignin）的實(shí)驗(yàn)在培養(yǎng)植物材料的階段失敗了卻讓我們了解了提供有效空氣流通的重要性。 **
In the absence of weight, there is poor water and air movement through the rooting media. One complication we've discovered is that in microgravity, the water distributes evenly throughout the soil. This can actually prevent air from reaching the roots. That's why 'Veggie' uses wicks - so that water is only distributed to selected areas. It's also why a lot of study has gone into selecting the best soils. Fine grained soils hold too much water and coarse soils hold too much air.
** 由于在太空失重，只有很少的水分和流動(dòng)的空氣通過(guò)生根培養(yǎng)基，一個(gè)失重照成的并發(fā)癥就是水分會(huì)均勻分布在土壤中使得氣體無(wú)法到達(dá)根系，這就“Veggie”（一項(xiàng)太空植物研究）使用wicks，以便讓水分布在選擇的區(qū)域，這就是為什么許多研究選擇最好的土壤，好的細(xì)粒土保持了太多的水分而粗粒土保持了太多的空氣。**
Tropism is a growth response between a plant and external stimulus. There are numerous forms of tropism and understanding each of them greatly affects our abilities to grow healthy plants. One of the cool things about experimenting on the ISS is that we can study each form of tropism in isolation. On Earth, gravity tends to overwhelm the other influences.
向性：一種植物生長(zhǎng)方式取決于植物本身及外界環(huán)境的刺激，植物有許多的極性，它們對(duì)我們種植出健康的植物有巨大的影響，說(shuō)一件有趣的ISS經(jīng)歷，我們可以在隔離（isolation）的環(huán)境中研究各種向性，而在地球上，重力往往要大于其他的因素。
Gravitropism is when the external stimulus is gravity. Plants have a hormone called auxin. In a gravity environment, if a plant is oriented on its side, auxin will accumulate in the stem and stimulate cell expansion that will result in the stem bending to point upwards so that the stem grows towards light (the sun). Similarly, auxin prevents cell elongation in the roots and that encourages roots to grow downwards.
向地性：當(dāng)存在重力時(shí)，植物有一種稱之為生長(zhǎng)素（auxin）的植物激素，在重力環(huán)境中，當(dāng)植物極性分化后，生長(zhǎng)素會(huì)在莖中積累然后刺激細(xì)胞伸長(zhǎng)，導(dǎo)致莖干發(fā)生彎曲向上生長(zhǎng)以便植物能夠向著光源的方向生長(zhǎng)，同樣的生長(zhǎng)素能夠防止細(xì)胞伸長(zhǎng)以及促進(jìn)根系向下生長(zhǎng)。
When plants grow, they do so in an oscillatory or helical manner called circumnutation. We can easily see this in vines that grow around an object. An interesting experiment was done aboard the ISS to study this in the absence and presence of gravity in the space environment. Arabidopsis plants were grown from seeds in space and observed both in the normal microgravity environment and in a centrifuge that simulated 0.8 g. While under the 0.8 g, the plants experienced circumnutation amplitudes 5-10 times as high as in microgravity. Within the endodermis of the planet there are gravisensing cells. On a larger scale, this may mean that vines cannot twine in space.
當(dāng)植物生長(zhǎng)時(shí)，會(huì)發(fā)生搖擺或者旋轉(zhuǎn)方式叫做回旋運(yùn)動(dòng)（circumnutation），我們可以容易的看到這些藤圍繞著一個(gè)物體生長(zhǎng)，在ISS上我們做了一個(gè)有趣的實(shí)驗(yàn)，分別在失重（absence gravity）和存在重力（presence gravity）的條件下，擬南芥（Arabidopsis）在太空中發(fā)芽，觀察它們?cè)谑е丨h(huán)境和在0.8g刺激的離心機(jī)（centrifuge）中的表現(xiàn)，在0.8g刺激下，植物有規(guī)律的（experienced）回旋運(yùn)動(dòng)振幅5-10次遠(yuǎn)比失重（microgravity）環(huán)境要高，植物內(nèi)胚層（endodermis）是重力敏感（gravisensing）細(xì)胞，也就是說(shuō)，這意味著藤無(wú)法在失重的環(huán)境下纏繞（twine）。
An interesting thing learned from studying cucumber growth in space involves a structure called a peg that develops immediately after germination, between the root and stem. This peg has long been observed and the scientists were interested to see if it was dependent on gravity. What they learned was that each seed is structured to grow two pegs - one on each side - but in the presence of gravity, only one peg develops, whereas both are activated in microgravity.
可以從黃瓜（cucumber）的研究中發(fā)現(xiàn)一些有趣的事，太空中生長(zhǎng)的黃瓜在發(fā)芽后在根和莖的地方會(huì)長(zhǎng)出具有一個(gè)被稱為夾子（peg）的結(jié)構(gòu),科學(xué)家們一直在觀察這些peg是如何受到重力的影響的，他們只知道每顆種子會(huì)葬兩個(gè)pag，左右各一個(gè)，但在重力環(huán)境下只有一邊的pag會(huì)生長(zhǎng)，而在失重環(huán)境下兩邊都會(huì)。
*Studies indicate that a plant's perception of gravity is related to the presence of starch in the organelles within the cell structure of the roots. Roots with starch appear to be more sensitive to gravity that roots that are missing the starch. *
研究表明地球的重力的感知與根結(jié)構(gòu)細(xì)胞器中的淀粉（starch）有關(guān)，那些根中富含淀粉的相比不含淀粉對(duì)重力更為敏感。
Hydrotropism is when the external stimulus is water. Cucumber plants are particularly dependent on gravity to initiate growth. An experiment called Hyrop Tropi was conducted in the Japanese laboratory aboard ISS, in 2010. The experiment was designed to investigate two major objectives; one was to see if roots of cucumber seedlings would bend toward water when they grow in microgravity, and the other was to identify Auxin-regulated genes. This was a neat example of an experiment that needed microgravity. It would be difficult to study the role of water on Earth, because we can't easily remove the effects of gravity, but in space we could ensure that water was the only stimulus. Here's a brief summary of the results, from the principal investigator.
向水性：當(dāng)外界刺激為水時(shí)，黃瓜特別的依賴水來(lái)啟動(dòng)生長(zhǎng)，一項(xiàng)正在進(jìn)行的叫做Hyrop Tropi 的日本實(shí)驗(yàn)項(xiàng)目在ISS上進(jìn)行，2010年時(shí)，項(xiàng)目設(shè)計(jì)研究了兩個(gè)主要的對(duì)象，一個(gè)是研究在失重環(huán)境下黃瓜根系萌發(fā)的輕水性，其他組則負(fù)責(zé)識(shí)別生長(zhǎng)素調(diào)控基因，這是一個(gè)嚴(yán)格的（neat）實(shí)驗(yàn)因此需要在失重環(huán)境下進(jìn)行，這與在地球上研究水的角色十分的不同，因?yàn)槲覀儾豢赡茌p易的擺脫引力的影響。但是在太空中我們則可以讓刺激唯一，這是一則論文的簡(jiǎn)要概括。
- The results showed that roots hydrotropically bent toward the moistened plastic foam under microgravity conditions, whereas they grew straight along the direction of gravitational force under 1G conditions. The hydrotropic response in microgravity appeared to be greater in the NaCl chamber compared with that in H2O chamber, but they did not differ statistically. Furthermore, CsIAA1 gene differentially expressed in the hydrotropically bending roots; the expression was much greater on the concave side than on the convex side. On the other hand, no asymmetric expression of CsIAA1 in the roots grown under 1G conditions were detected. These results revealed that roots become very sensitive to moisture gradients in microgravity and that auxin redistribution and differential auxin response take place during hydrotropic response. Also, the results imply that the hydrotropic response can be used as a means of root growth regulation for plant production in space. (Hydrotropism and Auxin-Inducible Gene expression in Roots Grown Under Microgravity Conditions)
結(jié)果表明在失重與1G引力（gravitational）環(huán)境下根系在濕潤(rùn)可彈性海綿的方向生長(zhǎng)研究親水性，親水性在失重環(huán)境下表現(xiàn)出比H2O室更大的NaCl室，但是它們并沒(méi)有出現(xiàn)統(tǒng)計(jì)學(xué)上的不同，此外，CsIAA1基因在彎曲的根中表現(xiàn)不同；表達(dá)在彎曲的凹面相比在凸面更巨大，而在1G引力的環(huán)境下基因并沒(méi)有非對(duì)稱（asymmetric）表達(dá)，這些結(jié)果發(fā)現(xiàn)在失重環(huán)境下濕度的漸變（gradient）會(huì)會(huì)使根系變得更加敏感，并照成生長(zhǎng)素的重新分配，在親水響應(yīng)中不同的生長(zhǎng)素長(zhǎng)生，并且，這項(xiàng)研究暗示著向水性反應(yīng)可以作為一項(xiàng)有意義的根系生長(zhǎng)調(diào)節(jié)在太空的植物種植中。
Phototropism is when the external stimulus is light. In some of the pictures from space you'll notice that the lighting is red-blue in the plant habitat. Red-blue light that has been deemed most efficacious for photosynthesis.
向光性：當(dāng)外界刺激為光照的時(shí)候，從一些宇宙的照片可以發(fā)現(xiàn)宇宙發(fā)出的光為紅藍(lán)光，紅藍(lán)光被認(rèn)為是光合作用最高效的光源。
Other tropisms that can be studied are chemotropism (chemicals), thigmotropism (touch), and electrotropism (electric fields)In April, a SpaceX cargo vehicle delivered a plant growth chamber that the payload investigators call 'Veggie*'. The astronauts will use it to grow foods. 'Veggie' utilizes small bags of soil with inserted wicks to provide water. *
其它可以被研究的的向性包括化學(xué)向性（chemotropism）,擾（觸碰）向性（thigmotropisum）及電場(chǎng)向性（electropisumn）,四月份，一枚運(yùn)輸植物生長(zhǎng)室（chamber）的叫做“Veggie”的SpaceX運(yùn)載火箭，宇航員將會(huì)使用其生產(chǎn)事物，“veggie”利用穿插著燈芯的突然以提供水分。
One area that we don't yet have a lot of understanding is how much the spaceflight environment will influence metabolite production. Metabolites affect flavor and nutritional quality. The plan is to return early 'Veggie' crops to Earth to study the metabolites.
一個(gè)我們還不太了解的領(lǐng)域就是太空飛船環(huán)境如何的影響植物的代謝（metabolite），代謝影響著事物的味道（flavor）以及營(yíng)養(yǎng)物質(zhì)的含量，于是計(jì)劃盡早將“Veggie”作物運(yùn)回地球研究測(cè)定。
How Do Plants Grows in Microgravity？——Hideyuki Takahashi
I am interested in how plants adapt to and evolve in the space environment. Previous spaceflight experiments have confirmed that, as long as the environment is controlled with the right hardware, seeds can germinate, the resulting seedlings can grow, and the mature plants can bloom and bear fruit in space. However, the degree of growth is a different matter. A microgravity environment has a great impact on plant growth and development, and it eventually affects plant yield.
When plants migrated from the sea approximately 450 million years ago, they became land organisms. To do so, however, they had to overcome various environmental stresses, such as drought, in their terrestrial life. In order to avoid such stresses, sessile terrestrial plants evolved strategies to perceive light, water and gravity, and to respond to them by changing their growth orientation. Among these adaptive strategies, is gravimorphogenesis, in which plant growth is influenced by gravity. Examples of this phenomenon are: gravitropism, where roots grow downward and stems grow upward; circumnutation, where the stem or the root tips display helical or spiral movement (for example, a climbing vine shows remarkable circumnutation); and peg formation, which helps cucurbitaceous seedlings shed their seed coats . The space environment is an ideal place to study these mechanisms of gravity-dependent growth in the development of plants.
Gravitropism is a bending response, accomplished by differential growth of plant organs in response to gravity. On the space shuttle flight STS-95, which included Astronaut Chiaki Mukai, experiments were conducted to compare ground-grown and space-grown Arabidopsis and rice. On Earth, aerial parts of the plant (shoots) grow upward while roots grow downward. However, the experiments showed that in a microgravity environment, the growth direction is unregulated, and some roots even extend in the same direction as the aerial stems . In the case of root gravitropism, the hypothesis is that gravity is perceived by root cap cells, called columella, which are found at the root tips. Within the columella cells, starch-filled amyloplasts settle due to gravity, causing a change in the flow of the plant hormone auxin.
In essence, auxin characteristically flows in a fixed direction, from an aerial shoot, including the apical meristem and young leaves, towards the roots, through a central cylinder. After flowing down to the root tips by this polar transport, auxin begins to flow in the opposite direction, as if making a U-turn, along the roots. When roots are inclined and given gravitational stimulus, however, U-turning auxin tends to go downward instead of upward. As a result, the concentration of auxin increases in the lower part of the elongation zone in the inclined roots, causing a differential growth between the lower part and the upper part; the growth rate of the lower part decreases compared to that of the upper part causing the root to bend downward. This is how plant roots on Earth grow downward in response to gravity. However, in microgravity, amyloplasts do not settle within the root cap cells, so gravity is not perceived, nor is asymmetric auxin distribution induced. This is why, presumably, growth direction is uncontrolled in space.
You have probably seen Morning Glory vines growing upward, spiraling around a pole. This is thanks to circumnutation, which also has something to do with gravity. Previous studies have shown that stem circumnutation requires an endodermis, surrounding vascular tissue and made up of gravisensing cells. In a nutshell, without the so-called SCARECROW gene, which is essential for the proper differentiation of endodermal cells, the Morning Glory cannot sense gravity, and as a result, cannot circumnutate - its vines cannot twine. This indicates that circumnutation and spiral growth are gravity-dependent phenomena. I am very much looking forward to seeing whether circumnutation, or twining of vine plants, can be observed in the weightlessness of space.!
Peg formation on cucurbits - the plant family that includes cucumbers, melons and squash - is also influenced by gravity. A peg, which is a small protuberance, develops immediately after germination in the transition zone between root and stem . On Earth, the downward growth (gravitropism) of the roots results in a curvature at the transition zone. When seeds germinate in a horizontal or inclined position, a peg develops on the lower, concave side of the bending transition zone at an early stage of seedling growth. As such, it had been presumed that peg formation was regulated by gravity. When we germinated cucumber seeds in space , a peg formed on each side of the transition zone, showing that pegs develop with or without gravity. In other words, cucumber seedlings have the innate ability to develop two pegs, but on Earth, the seedlings suppress peg formation on the upper side of the inclined transition zone in response to gravity, which causes unilateral placement of the peg in cucumber seedlings. This gravity regulation has something to do with auxin, the plant hormone I mentioned earlier.
To sum up, plant life depends on gravity, and auxin transport, which is regulated by gravity, plays an important role. It is thought that in the weightlessness of space the absence of gravity to regulate auxin transport results in abnormal growth and development of plants. However, exactly how gravity regulates auxin transport remains unknown. When this mechanism is understood, it will not only improve plant production on Earth, but will also help with plant cultivation in space. So, it is very important to perform space experiments that will clarify the mechanisms of plant growth and development.Dr. Hideyuki TakahashiProfessor, Graduate School of Life Sciences, Tohoku UniversityIn 1982, Dr. Takahashi received his Ph.D. in Agriculture from the Graduate School of Agricultural Science at Tohoku University, and a postdoctoral fellowship at the Department of Biology at Wake Forest University, in North Carolina, USA. He was a research associate at the Institute for Agricultural Research at Tohoku University from 1985 to 1987, and at the Institute of Genetic Ecology at Tohoku University in 1988. The following year he was a visiting fellow at the Department of Biology of the University of North Carolina at Chapel Hill (North Carolina, USA). Subsequently, Dr. Takahashi was appointed associate professor, and as of 1996, a full professor, at the Institute of Genetic Ecology at Tohoku University. He has been in his current position since 2001.
