内容来源：https://www.quantamagazine.org/the-hidden-mathematical-dance-inside-plant-cells-20260504/

内容总结：

植物细胞内的“数学之舞”：科学家揭示叶绿体如何实现光能利用与避害的最优解

对于依赖阳光生存的植物而言，光线既是生存的源泉，也潜藏着致命的风险。从柔和的晨光到正午的烈日，从短暂的荫蔽到骤然曝晒，植物必须应对光线强度瞬息万变的挑战。近日，荷兰阿姆斯特丹大学医学中心与阿姆斯特丹大学的联合研究团队在《美国国家科学院院刊》（PNAS）上发表了一项突破性研究，揭示了一种常见水草——伊乐藻（Elodea）的叶绿体如何通过自组织行为，实现一种数学意义上的最优排列：既紧密覆盖细胞表面以充分吸收光能，又在必要时留有足够空间灵活移动以避免强光伤害。

光的“双刃剑”：叶绿体的生死抉择

“光是叶绿体最好的朋友，也是最坏的敌人。”该研究的指导教师、阿姆斯特丹大学物理学家马齐·贾拉尔（Mazi Jalaal）形象地解释道。叶绿体负责将光能转化为植物所需的糖分，但光线过强时，它们必须迅速“逃离”至细胞壁的阴影区域。这种像羊群躲避烈日般的动态行为，一直是生物物理学家关注的谜题。

研究第一作者尼科·施拉玛（Nico Schramma）发现，伊乐藻叶绿体在细胞内并非随机分布，而是遵循一种精密的“自组织”规律。通过显微镜观察，他注意到这些呈圆盘状的细胞器在细胞表面均匀散布，如同精心摆放的硬币。贾拉尔教授敏锐地意识到，这背后隐藏着一个古老的数学问题——“堆积问题”（the packing problem），即如何在有限空间内实现效率最大化的排列。

“玻璃态”与数学最优解：进化设计的杰作

为了验证这一假设，研究团队联手软物质物理学家埃里克·威克斯（Eric Weeks），利用理论物理算法构建了包含30至130个不同直径圆盘的二维模型。模拟结果显示，当伊乐藻细胞保持特定大小和形状时，叶绿体的覆盖面积恰好达到细胞表面积的70%至80%，这一密度既能捕捉充足光线，又能为躲避强光预留出足够的移动空间。施拉玛随后在真实伊乐藻叶片中实测数据，结果与模型预测高度吻合。他一度怀疑计算错误，反复验证后才确信：“叶绿体确实以数学上的最优方式堆积在一起。”

此前，该团队在2023年已发现伊乐藻细胞处于一种“玻璃态转变”的临界点：环境稳定时细胞呈固态，叶绿体固定；当光照突变，细胞内部流动性增强，叶绿体便可像流体中的颗粒般自由移动，甚至三维堆叠于细胞壁旁以自我保护。

进化之选还是偶然巧合？

这一精妙的排列模式究竟是自然选择的产物，还是其他进化压力的副产品？未参与研究的进化生物学家达科塔·麦考伊（Dakota McCoy）认为，这是自然选择“残酷之手”的完美体现：“如果不够高效或不够灵活，物种很容易灭绝。”她赞叹道，这项研究充分展示了进化作为“设计师”的伟大。

施拉玛本人则保持谨慎。2023年，实验植物学家卡塔日娜·格沃瓦茨卡（Katarzyna Glowacka）试图让烟草叶绿体缩小以获得更灵活的光合效率，却遭遇植物“抗拒”，暗示自然尺寸已是进化最优解。贾拉尔教授表示，未来需在其他植物甚至藻类中验证这是否具有普遍性：“在物理学中，我们追求普适规律；在生物学中，我们拥抱多样性和非普适性。”

这一发现不仅深化了对植物细胞内部精密调控机制的理解，也为仿生材料设计和农业光能利用优化提供了全新视角。正如贾拉尔所言：“植物在进化历程中需要解决无数物理问题，而叶绿体堆积之谜，只是其中精彩的一章。”

中文翻译：

植物细胞内部隐藏的数学舞蹈
引言
依赖阳光生存是一场危险的游戏。太阳光线不仅携带紫外线，可能断裂DNA链并降解分子，而且其强度也变化剧烈。植物必须忍受并茁壮成长——从柔和的晨光到炽热的夏日午后，从瞬间的阴影到全日照。它们获得的太阳能如同涓涓细流——或如洪水倾泻。

“想象一片云遮住太阳，突然云层飘过，阳光直射叶片。”阿姆斯特丹大学医学中心的生物物理学家尼科·施拉玛说，“必须有所变化，因为光强度可能骤增百倍。”

植物并非被动承受。它们会做出相应反应。它们可以通过旋转叶片和茎干来调整方向以寻找阳光或阴影，但这种机制在几分钟或几小时内起作用。对于更精细的反应，它们的细胞也必须行动起来。每个植物细胞内都含有叶绿体——一种将阳光转化为糖分的盘状细胞器。虽然植物大多保持静止，但叶绿体却并非如此。

“叶绿体会移动。”施拉玛说。他将它们的行为比作羊群在晴天寻找阴凉：强光同样会将叶绿体驱赶到细胞壁旁的阴影区域。

“阳光是叶绿体最好的朋友，也是最坏的敌人。”指导施拉玛博士研究的阿姆斯特丹大学生物物理学家马齐·贾拉尔说，“它们需要阳光进行光合作用。但一旦光强度过高，它们就必须逃离。”

最近，施拉玛和贾拉尔专注于叶绿体物理中的一个谜团。每个细胞器如何在植物对光的渴望与对过强光的厌恶之间取得平衡？反过来，这又如何表现为细胞内的模式？2025年秋季，他们在《美国国家科学院院刊》上报告称，他们用作模式植物的普通水族箱水草——伊乐藻中的叶绿体，自我组织成某种数学上的最优状态。它们密集地覆盖细胞表面以吸收充足的光线，同时稀疏地分布在细胞中，以便在需要时能够灵活移动并有效隐藏。

“我们在这里看到的美丽之处，是进化这位伟大的设计师。”芝加哥大学研究光合作用的进化生物学家达科塔·麦考伊说，“当你在论文中看到某种东西与你的模拟完美契合时……这是巧合，还是它进化成了那样？”

自然的数学
贾拉尔进入这一领域的过程听起来像是个笑话。他的母亲教高中生物，父亲教高中物理。家人曾争论这个少年未来职业的方向。于是，他便成了生物物理学家。

“[我们实验室的]问题始终是生物学问题。”贾拉尔说，“但你常常会立即发现，必须解决一个物理问题才能回答那些生物学问题。”

植物引发了许多这样的问题。2021年，当他与施拉玛为新项目来回讨论想法时，他们了解到了伊乐藻（Elodea densa）。伊乐藻相当普通：是家庭水族箱和中学科学课的必备品。这种水草的优点在于叶片简单，比陆生植物更容易在显微镜下观察。对研究人员来说，这为提出新问题提供了捷径。“这些生物在进化过程中必须解决许多物理问题。”贾拉尔说。

在观看了一些YouTube视频后，他们在网上订购了这种植物。施拉玛摘取了一些厘米长的叶片。在显微镜下，它们像一堵由矩形细胞构成的砖墙。叶绿体在每个细胞中从头到尾清晰可见地散布着。他很快观察到一个植物生物学家熟悉的现象：叶绿体以各种大小生长，分散开来收集光线，或聚集在细胞侧壁以保护自己。

“在显微镜下观察它们时，这令人惊叹。”贾拉尔说。他好奇这些不均匀的小块如何能在不同光照条件下如此有序地组织。

他们了解到，很少有植物生物学家详细研究过叶绿体的运动。两位先驱——印第安纳大学的罗杰·汉加特和东京都立大学的和田正光——已经退休。和田早在20世纪90年代就开始研究叶绿体运动，通过观察这些细胞器如何通过萌发细胞骨架纤维（包括肌动蛋白和微管）来移动或固定自己。汉加特研究了这些机制，以及数十种不同植物物种中叶绿体的几何形状。

“保护确实非常重要。”汉加特说，“如果你不能让叶绿体移动，它们很可能会受损，然后你就得消耗能量来修复它们。这甚至可能杀死植物。”

贾拉尔发现，对于每一个可能的生物学问题，相关的物理原理都未被充分探索。物理学家知道，各种微小单元可以通过简单的相互作用自组织成庞大而复杂的结构——这一现象广泛称为涌现。想象一下椋鸟群如墨滴般染黑天空，或羊群如液体般流动。自组织与数学在所谓的堆积问题中交汇，这一问题可追溯至约翰内斯·开普勒。这位以行星运动研究闻名的17世纪天文学家提出，堆叠球体最密集的方式是将它们排列成金字塔形，就像你在杂货店摆放橙子那样（在二维空间中，这个问题更像是在平坦桌面上排列硬币）。这看似显而易见，但证明它却相当具有挑战性，尤其是在更高维度或其他形状的情况下。

贾拉尔意识到，植物细胞必须解决自己的堆积问题：一堆大小不一的圆盘必须在强光和弱光下都能高效地组织和堆积。当他在显微镜下观察伊乐藻细胞时，他看到叶绿体均匀地堆积在细胞中。这表明植物中发生了一种“计算”，贾拉尔说：“甚至在研究叶绿体如何移动之前，[显微镜图像]就清楚地表明这里发生了很多事情。”

叶绿体在植物出现之前很久就进化了。大约30亿年前，一种细菌进化出了以光为食的化学工具。然后，10亿年后，另一个细胞吞噬了它而没有杀死它，并将这种细菌的光捕获工具据为己有。这种原始吞噬，创造了一种称为内共生的条件（也被认为是线粒体的起源故事），被认为只发生过一次。但它创造的杂交细胞非常适应环境，其后代繁衍成地球上所有的藻类和植物物种。“我们通常认为共生是小丑鱼和海葵那样的关系，但植物细胞与其驯化的叶绿体也是如此。”麦考伊说。

大约在19世纪初，显微镜学家注意到叶绿体在植物细胞中缓慢移动；几十年后，他们观察到这些细胞器对光做出反应。大约200年后，施拉玛将第二个鱼缸搬进实验室时，引来了周围物理学家好奇的目光。

堆积与移动
植物细胞是一个拥挤的场所。其内部空间大部分被一个充满液体的空泡——中央液泡占据，它对其他组分施加压力。夹在液泡和坚硬的细胞壁之间，叶绿体、细胞核和其他细胞器被挤压在植物细胞刚性的矩形壁旁。

叶绿体如何在拥挤中为自己开辟道路？汉加特和和田曾讨论过可能的机制：也许是蛋白质丝构成的细胞骨架在运送它，也许是叶绿体随机移动，也许是两者兼有。从生物物理学角度，贾拉尔和施拉玛想知道植物细胞如何组织其生存所依赖的叶绿体运动。

他们的答案：玻璃态行为。所谓的玻璃态转变发生在材料可在固态和液态之间可逆移动，而不经历完全的相变，就像鸡汤的胶状块在微热下融化，冷却后再次凝固。已知类似的转变发生在某些细菌细胞中。2023年，通过实验和数学建模的结合，施拉玛和贾拉尔报告称，伊乐藻细胞处于这种转变中的一个临界点。当光照条件恒定时，细胞稳定而坚实，叶绿体保持原位。当光强度变化引发活动时，致密的细胞内容物表现得更像液体。为了躲避光线，一些叶绿体甚至将自己藏在其他叶绿体后面，沿着细胞壁形成三维团簇——这种排列只有在细胞内部首先变得更加液态时才有可能。

但这个解释留下了未解之谜。叶绿体在细胞中大小、形状或密度的差异可能会使系统偏离玻璃态转变。“为什么是这种密度？为什么是这种形状？”施拉玛说，“这是否有意义？”

贾拉尔和施拉玛将问题重新定义为堆积问题。叶绿体是圆盘，在不同细胞中可以有各种大小和数量。它们的容器——矩形细胞——可以生长到几乎任意长度和宽度，但必须允许叶绿体在光线昏暗时堆积，并在光线强烈时沿细胞壁隐藏。在这些限制下，他们问道：植物细胞的大小和形状与叶绿体的大小和数量之间有什么关系？

与埃默里大学的软物质物理学家埃里克·威克斯合作，他们借用了理论物理中的一个算法。他们模拟了30到130个直径各异的圆盘，散布在一个固定长度和宽度的二维矩形内。起初，圆盘总共覆盖了盒子面积的1%。模拟依次放大一个圆盘，然后按相同生长因子放大另一个，以此类推。这个过程持续多轮——圆盘生长，空白空间缩小，生长因子收紧——直到圆盘无法再生长。此时，它们达到了所能达到的最密集堆积。

经过30,000次不同参数下的模拟，模型预测了细胞在最大化光吸收和避免光伤害方面的最佳几何形状。在这种细胞大小和形状下，叶绿体将拥有空间以单层最优堆积，从而最大化光吸收——填充细胞暴露表面积的70%至80%——同时仍有足够空间在需要时滑动到细胞壁以躲避光线。

但这仅仅是理论，是在笔记本电脑上想象并解决的一个完美世界。为了在真实生物学中验证这些发现，施拉玛将手臂伸入鱼缸，摘下更多叶片，并拍摄了其中细胞的显微图像，以测量伊乐藻的实际堆积比例。真实数据几乎完美地符合他的预测。

施拉玛起初不敢相信。“我几次冲进马齐[贾拉尔]的办公室，大喊‘我犯错了！’然后10分钟后：‘哦，其实没有！’”他回忆道，“我着迷般地反复检查。”

叶绿体确实以数学上最优的方式堆积。伊乐藻细胞足够小，使得内部特定组合的叶绿体能够紧密堆积以吸收最大光线，同时又足够大，使得叶绿体在需要时能够彼此移动以躲避光线。

当施拉玛思考这一结果对仍在生长的细胞（其形状会变化）意味着什么时，他得出结论，只有当细胞沿单一方向生长时，它们才能维持最优堆积。事实证明，伊乐藻细胞正是这样生长的。

选择还是巧合？
在自然界中发现一种模式是一回事；证明它是进化产物则是另一回事。要么叶绿体堆积进化到如研究人员所怀疑的那样优化了光吸收与规避，要么它源于对它们面临的其他压力的适应而偶然产生。

“我深信高效堆积本身就是进化的产物。”未参与该研究的麦考伊说，“自然选择之手是残酷的。如果你效率不够高或不擅长自己的任务，很容易灭绝。”

施拉玛本人对这一结论持谨慎态度。排除巧合需要证明叶片优先考虑其从特定大小的可移动叶绿体中获得的灵活性。一些这样的证据似乎存在。

在2023年的一项研究中，实验植物学家卡塔日娜·格沃瓦卡在内布拉斯加大学培育了具有不同大小叶绿体的烟草变种。她期望大量小型叶绿体能使叶片细胞成为更敏捷的光合作用者。但事实并非如此。事实上，让烟草缩小其叶绿体出乎意料地困难。“几乎就像植物有抵抗力一样。”格沃瓦卡说，“好像有什么东西阻止它们变得更小。”超小叶绿体可能是弱的光和二氧化碳收集器，或者它们可能被挤得太紧，就像大房子的东西塞进了小公寓。她得出结论，烟草叶绿体的自然大小是最优的。

对贾拉尔来说，更确定的结论需要观察其他植物的这些特征。答案可能因物种而异，也与其他光合作用生物（如藻类）不同。伊乐藻对其叶绿体问题的解决方案可能广泛存在——或者完全独特。唯一确定的方法是去观察。

“在物理学中，我们追求普适性。”贾拉尔说，“在生物学中，我们拥抱非普适性和生物多样性。”

英文来源：

The Hidden Mathematical Dance Inside Plant Cells
Introduction
Living on light is a dangerous game. Not only do the sun’s rays carry ultraviolet waves that can snap DNA strands and degrade molecules, but they also vary wildly in intensity. Plants must endure and thrive through soft morning light and blazing summer afternoons, through shade one moment and full sun the next. Their solar calories come in a trickle — or a deluge.
“Think of a cloud obscuring the sun, and suddenly the cloud passes and the sun ray hits a leaf,” said Nico Schramma, a biophysicist at Amsterdam University Medical Center. “Something has to change because the intensity might change a hundredfold.”
Plants aren’t passive. They respond accordingly. They can reorient themselves by rotating their leaves and stems to seek sunbeams or shade, but this mechanism works on a scale of minutes or hours. For finer responses, their cells must mobilize as well. Within every plant cell are chloroplasts, disc-shaped organelles that turn sunlight into sugars. And while plants have to remain mostly stationary, chloroplasts do not.
“Chloroplasts move,” Schramma said. He likened their behavior to that of a flock of sheep seeking shade on a bright day: Intense light similarly shepherds chloroplasts into shaded patches along the cell wall.
“Light is the best friend and worst enemy of chloroplasts,” said Mazi Jalaal, a biophysicist at the University of Amsterdam who supervised Schramma’s doctoral work. “They need it for photosynthesis. But the moment the light intensity goes too high, they have to run away from it.”
Recently, Schramma and Jalaal have obsessed over a mystery of chloroplast physics. How does each organelle balance the plant’s appetite for light with its distaste for too much? And how, in turn, is this expressed as patterns within a cell? In fall 2025 in the Proceedings of the National Academy of Sciences, they reported that the chloroplasts in Elodea, a common aquarium waterweed that they use as a model plant, self-organize into a sort of mathematical optimum. They pack their cell’s surface densely enough to absorb ample light while populating the cell sparsely enough to meander and hide efficiently when they need to.
Courtesy of Nico Schramma
“The beautiful thing we see here is what a great designer evolution is,” said Dakota McCoy, an evolutionary biologist studying photosynthesis at the University of Chicago. “When you see something fit your simulation really, really well, like this paper does … is it a coincidence, or is it that it evolved to be that way?”
Natural Math
Jalaal’s path to this field sounds like a punch line. His mother taught high school biology. His father, high school physics. The family debated which direction the teenager would go in his career. Voilà, biophysics.
“[Our lab’s] questions always are biology questions,” Jalaal said. “Often you immediately find out that you must solve a physics problem to solve those biological questions.”
Plants provoke many such questions. In 2021, as he and Schramma ping-ponged ideas for a new project, they learned about Elodea densa. Elodea is rather unextraordinary: a staple in home aquariums and middle school science classes. In its favor, the waterweed has simple leaves, which are easier to inspect under a microscope than those of land plants. For the researchers, this offered a shortcut to new questions. “There are so many physics problems that these organisms have to solve during the course of evolution,” Jalaal said.
Courtesy of Mazi Jalaal
After watching some YouTube videos, they ordered the plant online. Schramma pinched off some centimeter-long leaves. Under the microscope they resembled a brick wall of rectangular cells. Chloroplasts visibly freckled each cell from end to end. He soon made the observation — familiar to plant biologists — that chloroplasts grow in a medley of sizes and fan out to collect light or huddle against cellular side walls to shield themselves from it.
“It is striking when you look at them on the microscope,” Jalaal said. He wondered how the uneven blobs manage to organize so neatly under different light conditions.
They learned that few plant biologists had studied chloroplast motion in great detail. Two trailblazers — Roger Hangarter from Indiana University and Masamitsu Wada from Tokyo Metropolitan University — were retired. Wada had begun experimenting with chloroplast motion back in the 1990s by looking into how the organelles move or anchor themselves by sprouting cytoskeletal fibers, including actin and microtubules. Hangarter had studied these mechanics, as well as the geometry of chloroplasts, in dozens of different plant species.
“Protection’s a real important thing,” Hangarter said. “If you can’t move your chloroplasts, they’re likely to get some damage, and then you’ve got to expend energy repairing them. It could even kill the plant.”
For every possible biological inquiry, Jalaal found, the physics involved was under-explored. Physicists know that small units of all sorts can self-organize into large, complicated structures from simple interactions — a phenomenon known broadly as emergence. Picture murmurations of starlings staining the sky like ink drops or flocks of sheep flowing like liquid. Self-organization intersects with mathematics in so-called packing problems, which date back to Johannes Kepler. The 17th-century astronomer, best known for his studies of planetary motion, proposed that the densest way to stack spheres is to arrange them in a pyramidal pile, the way you’d set out oranges in a grocery store (in two dimensions, this problem is more like arranging pennies on a flat tabletop). This might seem obvious, but proving it was quite challenging, especially for higher dimensions or other shapes.
Plant cells must solve their own packing problem, Jalaal realized: A handful of discs in different sizes must organize and pack themselves efficiently in both bright and dim sunlight. When he looked at Elodea cells under the microscope, he saw chloroplasts packing the cell evenly. This suggested a sort of “computation” occurring in the plant, Jalaal said. “Even before going to how chloroplasts move, [the microscope image] was a clear sign there’s so much happening here.”
Chloroplasts evolved long before plants did. Around 3 billion years ago, a bacterium evolved the chemical tools to feed on light. Then, a billion years later, another cell swallowed one without killing it and took the bacterium’s light-harvesting tools for itself. This primordial gulp, creating a condition known as endosymbiosis (also thought to be the origin story of mitochondria), is believed to have happened just once. But the hybrid cell it created was so fit that its descendants blossomed into every alga and plant species on Earth. “We think of symbiosis as something like a clown fish and an anemone, but a plant cell with its domesticated chloroplasts is also,” McCoy said.
Around the early 1800s, microscopists noticed chloroplasts ambling around plant cells; decades later, they observed the organelles reacting to light. Some 200 years after that, Schramma earned curious looks from neighboring physicists as he carried a second fish tank into his lab.
Courtesy of Nico Schramma
Packing and Moving
A plant cell is a crowded venue. Much of its inner volume is taken up by a fluid-filled blob — the central vacuole — that exerts pressure on other occupants. Caught between a vacuole and a hard place, the chloroplasts, nucleus, and other organelles are smushed against the plant cell’s rigid rectangular walls.
How might a chloroplast elbow its way through the crowd? Hangarter and Wada had debated the possible mechanics: Maybe the cytoskeleton of protein filaments ferries it about, maybe the chloroplast buzzes along randomly, maybe a mix of both. From the biophysical side, Jalaal and Schramma wondered how a plant cell can organize the movement of its chloroplasts, which its survival depends on.
Their answer: glassy behavior. A so-called glass transition occurs when a material can reversibly move between solid and liquid states without undergoing a full phase transition, the way a gelatinous glob of chicken stock melts with a little heat and solidifies again when cool. A similar transition is known to happen in some bacterial cells. In 2023, using a combination of experiments and mathematical modeling, Schramma and Jalaal reported that Elodea cells occupy a critical point at such a transition. When light conditions are constant, the cell is stable and firm, and chloroplasts remain in place. When a change in light intensity prompts activity, the dense cellular contents behave more like a liquid. To hide from light, some chloroplasts even tuck themselves behind others in a 3D cluster along the cell wall — an arrangement that’s only possible if the cell interior becomes more fluidlike first.
But that explanation left questions open. Differences in the size, shape, or density of chloroplasts in the cell could steer the system away from a glassy transition. “Why this density? Why this shape?” Schramma said. “Does it mean anything?”
Jalaal and Schramma reframed their question as a packing problem. The chloroplasts are discs that can come in various sizes and quantities in different cells. Their container, a rectangular cell, can grow to virtually any length and width — but must allow chloroplasts to pack when lights are dim and hide along its walls when light shines brightly. Given those constraints, they asked, what is the relationship between the plant cell’s size and shape and the chloroplasts’ size and number?
Working with the soft matter physicist Eric Weeks at Emory University, they borrowed an algorithm from theoretical physics. They programmed 30 to 130 discs, which varied in diameter, to scatter around a two-dimensional rectangle of fixed length and width. At first, the discs collectively covered 1% of the box. The simulation enlarged first one disc and then another by the same growth factor, and so on. The process continued for many rounds — discs grew, empty space shrank, the growth factor tightened — until the discs could no longer grow. At that point they were as densely packed as they were going to get.
After 30,000 simulations under a slew of parameters, the model predicted an optimal geometry for the cells to maximize both light absorption and avoidance. At this cellular size and shape, chloroplasts would have the space to pack optimally in a single layer to maximize light absorption — filling a cell’s exposed surface area between 70% and 80% — while still having enough room to shuffle away to the walls to avoid the light when they needed to.
But this was just theory, a perfect world imagined and solved on a laptop. To prove out the findings in real biology, Schramma stuck his arm back into the fish tank, nipped more leaves, and snapped microscope images of the cells within to measure Elodea’s actual packing fractions. The real data matched his predictions almost perfectly.
Schramma couldn’t believe it at first. “I ran a couple of times into Mazi [Jalaal]’s office like, ‘I made a mistake!’ Then, 10 minutes later: ‘Oh, actually, no!’” he recalled. “I was obsessed with checking.”
The chloroplasts were indeed packed in a mathematically optimal way. The Elodea cells were small enough for the particular assemblage of chloroplasts within to pack themselves tightly to absorb maximum light, and large enough for chloroplasts to maneuver around one another to avoid it when needed.
When Schramma considered what the result meant for still-growing cells (which change shape), he concluded that cells would maintain optimal packing only if they grew in a single direction. Turns out, that’s how Elodea cells grow.
Selection or Serendipity?
Finding a pattern in nature is one thing; proving that it is an evolutionary product is another. Either chloroplast packing evolved to optimize light absorption and avoidance as the researchers suspected, or it arose coincidentally out of adaptations to other pressures they face.
“I’m very convinced that efficient packing is itself the product of evolution,” said McCoy, who was not involved in the study. “The hand of natural selection is brutal. If you’re not efficient enough or not good enough at your job, it’s pretty easy to go extinct.”
Schramma himself is cautious about this conclusion. Ruling out a coincidence would require proof that a leaf prioritizes the versatility it gets from mobile chloroplasts of a particular size. Some such evidence appears to exist.
In a 2023 study, the experimental botanist Katarzyna Glowacka grew tobacco variants with different-size chloroplasts at the University of Nebraska. She expected an army of small chloroplasts to make leaf cells more agile photosynthesizers. It didn’t. In fact, getting tobacco to shrink its chloroplasts was surprisingly difficult. “It’s almost like the plant was resistant,” Glowacka said. “Almost like there is something stopping them from getting smaller.” Ultra-small chloroplasts could be weak collectors of light and carbon dioxide, or they may be crammed too tightly, like the contents of a large home stuffed into a studio apartment. She concluded that the natural size of tobacco chloroplasts was optimal.
To Jalaal, a firmer conclusion will require looking at these traits in other plants. The answer may differ from species to species, and among other photosynthesizers such as algae. Elodea’s solution to its chloroplast problem could be widespread — or totally unique. The only way to know for sure is to look.
“In physics, we search for universality,” Jalaal said. “In biology, we embrace non-universality and biodiversity.”