Molecule Masterminds: Scientists Solve 50-Year-Old Mystery Behind Plant Growth

Alfalfa Sprouts Growth Timelapse

Timelapse of alfalfa sprouts growing (including roots and leaves) to represent fast plant growth.

Molecule masterminds elaborate growth process.

A team of researchers led by UC Riverside has demonstrated for the first time one way that a small molecule turns a single cell into something as large as a tree.

For half a century, scientists have known that all plants depend on this molecule, auxin, to grow. Until now, they didn’t understand exactly how auxin sets growth in motion. 

The word auxin is derived from the Greek word “auxein,” meaning “to grow.” There are two main pathways that auxin uses to orchestrate plant growth, and one of them is now described in a new Nature journal article. 

Plant cells are encased in shell-like cell walls, whose primary layer has three major components: cellulose, hemicellulose, and pectin. 

“Cellulose works like rebar in a high rise, providing a broad base of strength. It’s reinforced by hemicellulose chains and sealed in by pectin,” said UCR botany professor and research team leader Zhenbiao Yang.

Zhenbiao Yang

Professor and cell biologist Zhenbiao Yang with Arabidopsis plants used in his research. Credit: Zhenbiao Yang/UCR

These components define the shape of plant cells, resulting in sometimes-surprising formations like the puzzle-piece-shaped leaf epidermis cells that Yang has been studying for the last two decades. These shapes help tightly glue cells together and provide physical strength for plants against elements such as the wind.  With everything locked so tightly by the cell walls, how is movement and growth possible?

One theory posits that when plants are ready to grow, auxin causes their cells to become acidic, loosening the bonds between components and allowing the walls to soften and expand. This theory was proposed half a century ago, but how auxin activates the acidification remained a mystery until now. 

Yang’s team discovered auxin creates that acidity by triggering the pumping of protons into the cell walls, lowering their pH levels. The lower pH activates a protein, expansin, appropriately named because it breaks down links between cellulose and hemicellulose, allowing the cells to expand. 

The pumping of protons into the cell wall also drives water uptake into the cell, building inner pressure. If the cell wall is loose enough and there is enough pressure inside the cell, it will expand.

Plant Cell Components

Illustration of plant cell components. Credit: Caroline Dahl

“Like a balloon, expansion depends on how thick the outsides are, versus how much air you’re blowing in,” Yang explained. “Lowering the pH in a cell wall can allow water outside of a cell to move in, fueling turgor pressure and expansion.”

There are two known mechanisms by which auxin regulates growth. One is the pH lowering that Yang’s team described. Another is auxin’s ability to turn on gene expression in the nucleus of the plants’ cells, which in turn increases the amount of expansion and other growth-regulating factors in the cell.

The latter mechanism also lowers the pH of the cell and facilitates growth. UC San Diego professor of cell biology Mark Estelle is a leading authority in this field. He discovered and researched this other mechanism.

“Dr. Yang’s recent work represents a significant advance in our understanding of how auxin regulates cell expansion. It’s been known that acidification of the extracellular space promotes cell expansion but it wasn’t known how this happens,” Estelle said. “It’s exciting to see an old problem being solved.”

It is an understatement to say that auxin simply “contributes” to plant growth. It is essential to nearly every aspect of a plant’s growth and development, including aspects that are important to agriculture such as fruit, seed and root development, shoot branching, and leaf formation. Even the plant’s correct responses to gravity and light depend on auxin to ensure roots head down while the shoots grow up toward light.

Not only could a deeper understanding of auxin benefit agriculture and renewable energy production, it could one day influence medicine as well. “Understanding how the basic biology works may eventually have an impact on human health,” Yang said. “As our knowledge expands, we may learn that processes in humans are analogous.”

Reference: “TMK-based cell-surface auxin signalling activates cell-wall acidification” by Wenwei Lin, Xiang Zhou, Wenxin Tang, Koji Takahashi, Xue Pan, Jiawei Dai, Hong Ren, Xiaoyue Zhu, Songqin Pan, Haiyan Zheng, William M. Gray, Tongda Xu, Toshinori Kinoshita and Zhenbiao Yang, 27 October 2021, Nature.
DOI: 10.1038/s41586-021-03976-4

5 Comments on "Molecule Masterminds: Scientists Solve 50-Year-Old Mystery Behind Plant Growth"

  1. Babu G. Ranganathan | November 21, 2021 at 9:36 am | Reply

    Babu G. Ranganathan*
    (B.A. Bible/Biology)


    JUST BECAUSE something exists in nature does not mean it was invented by nature. If all the chemicals (i.e. amino acids, nucleic acids, etc.) necessary to make a cell were left to themselves, “Mother Nature” would have no ability to organize them into a cell. It requires an already existing cell to bring about another cell. The cell exists and reproduces in nature but nature didn’t invent or design it! Nature didn’t originate the cell or any form of life. An intelligent power outside of nature had to be responsible.

    Miller, in his famous experiment in 1953, showed that amino acids (the building blocks of life) could form by chance. But, it’s not enough just to have amino acids. The various amino acids that make-up life must link together in a precise sequence, just like the letters in a sentence, to form functioning protein molecules. It has never been shown that various amino acids can bind together into a sequence by chance to form protein molecules.

    Natural laws may explain how an airplane or cell works, but it’s not rational to believe that undirected natural laws can bring about an airplane or a cell.

    ONCE YOU HAVE a complete and living cell then the genetic program (or code) and biological machinery exist to direct the formation of more cells, but how could the cell have originated naturally when no directing code and mechanisms existed in nature?

    Mathematicians have said any event in the universe with odds of 10 to 50th power or greater is impossible! The probability of just an average size protein molecule arising by chance is 10 to the 65th power. Even the simplest cell is made up of many millions of various protein molecules along with and DNA/RNA..

    The late great British scientist Sir Frederick Hoyle calculated that the odds of even the simplest cell coming into existence by chance is 10 to the 40,000th power! How large is this? Consider that the total number of atoms in our universe is 10 to the 82nd power.

    The cell didn’t evolve. A partially evolved cell would quickly disintegrate, not wait millions of years to become complete and living.

    WHAT ABOUT EVOLUTION? Only evolution within “kinds” is genetically possible (i.e. varieties of dogs, cats, horses, cows, etc.), but not evolution across “kinds” (i.e. from sea sponge to human). How could species have survived if their vital tissues, organs, reproductive systems were still evolving? Survival of the fittest would actually have prevented such evolution! Only limited evolution, variations of already existing genes and traits, is possible. Nature is mindless and has no ability to design and program entirely new genes for entirely new traits.

    WHAT ABOUT NEW SPECIES: Although new species have come into existence, they don’t carry any new genes. They’ve become new species only because they can’t be crossed back with the original parent stock for various biological reasons. A biological “kind” allows for new species but not new genes. Nature has no ability to invent new genes for new traits. Only limited variations and adaptations are possible in nature, and all strictly within a biological “kind” (i.e. varieties of dogs, cats, etc.).

    All species of plants and animals in the fossil record are found complete, fully formed, and fully functional. This is powerful evidence that all species came into existence as complete and fully formed from the beginning. This is only possible by creation.

    What about natural selection? Natural selection doesn’t produce biological traits or variations. It can only “select” from biological variations that are possible and which have survival value. That’s why it’s called natural “selection.” The real issue is what biological variations are possible, not natural selection. Only variations and mutations of already existing genes or traits are possible.

    Dr. Randy J. Guliuzza’s extensive research points to a better explanation than natural selection for variation and adaptation in nature. Dr. Guliuzza explains that species have pre-engineered mechanisms that enable organisms to continuously track and respond to environmental changes with system elements that correspond to human-designed tracking systems. This model is called CET (continuous environmental tracking). His research strongly indicates that living things have been pre-engineered to produce the right adaptations and changes required to live in changing environments. It’s much like a car that’s been pre-engineered so that the head lights turn on automatically when day changes to night.

    Modern evolutionists believe and hope that over, supposedly, millions of years, random mutations in the genetic code caused by environmental radiation will generate entirely new genes for natural selection to use. This is total blind and irrational faith on the part of evolutionists. It’s much like believing that randomly changing the sequence of letters in a romance novel, over millions of years, will turn it into a book on astronomy! That’s the kind of blind faith macro-evolutionists have.

    Mutations are accidents in the genetic, are mostly harmful, and have no capability of producing greater complexity in the code. Even if a good accident occurred, for every good one there would be hundreds of harmful ones with the net result, over time, being harmful, even lethal, to the species. Even if a single mutation is not immediately harmful, the accumulation of mutations over time will be harmful. At best, mutations only produce further variations within a natural species. Most biological variations are not due to mutations but from new combinations of already existing genes.

    What about genetic and biological similarities between species? Genetic information, like other forms of information, cannot happen by chance, so it is more logical to believe that genetic and biological similarities between all forms of life are due to a common Designer who designed similar functions for similar purposes. It doesn’t mean all forms of life are biologically related! Only genetic similarities within a natural species proves relationship because it’s only within a natural species that members can interbreed and reproduce.

    The actual similarity between ape and human DNA is between 70-87% not 99.8% as commonly believed. The original research stating 99.8% similarity was based on ignoring contradicting evidence. Only a certain segment of DNA between apes and humans was compared, not the entire DNA genome.

    All the fossils that have been used to support human evolution have been found to be either hoaxes, non-human, or human, but not non-human and human (i.e. Neanderthal Man was discovered later to be fully human).

    There has never been unanimous agreement among evolutionary scientists on ANY fossil evidence that has been used to support human evolution over the Many years, Including LUCY.

    Also, so-called “Junk DNA” isn’t junk. Although these “non-coding” segments of DNA don’t code for proteins, they have recently been found to be vital in regulating gene expression (i.e. when, where, and how genes are expressed, so they’re not “junk”).

    Read the author’s Internet article, NO MEAT-EATING ANIMALS EXISTED IN THE BEGINNING

    Visit my latest Internet site: THE SCIENCE SUPPORTING CREATION (This site answers many arguments, both old and new, that have been used by evolutionists to support their theory)


    * I have had the privilege of being recognized in the 24th edition of Marquis “Who’s Who In The East” for my writings on religion and science, and I have given successful lectures (with question and answer time afterwards) defending creation from science before evolutionist science faculty and students at various colleges and universities.

  2. Andres Albarran | November 21, 2021 at 3:28 pm | Reply

    Now if only one could harness auxin turn it into an encryption that in itself is capable of causing subatomics to grow out into atomics through the process of photosynthesis. something that would be implantable into say the four Gas giants as to cause growth in mass while subsequently creating a secondary form of viral encryption that which causes the inner layers of the atmosphere to continuesly condense and solidify as the outermost layer grows endlessly. it’d shrink yet gain weight a process that would create a fusion capable core that which could be implanted with a third yet not final encryption as to cause an ignition without detonation which means no dispersement of energtic force. the end yet not final result would be successfully creating a microstar that which over time would be implanted with even more encryptions that’d cause the micro to grow into dwarf and so on. doing the same to the center star would grants us over centuries a five star system that which consists of stars that would never die because they’d absorb light rays as a food source to maintain and grow in size.

  3. Steve Nordquist | November 22, 2021 at 9:40 am | Reply

    Thanks for this fine basic science work, published open access! Thrilled also to see vegetable growth stimulation affecting animals as schizophrenia, hey that’s the way microbiology and homeopathy meet up 10^24 times to one.

  4. I share the opinion above and have also read the facts regarding evolution. There is ample evidence that all creatures are created entities, not the result of evolution and random processes.
    Evolution only works with fully formed living systems, not from soil, water and sun to proteins and sentient beings.
    Now who did this creation is the ultimate question.

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