Corporate Banner
Satellite Banner
Scientific Communities
Become a Member | Sign in
Home>News>This Article

Stanford Researchers Solve Plant Sex Cell Mystery

Published: Wednesday, August 08, 2012
Last Updated: Wednesday, August 08, 2012
Bookmark and Share
For millennia, sex cells have stubbornly guarded the secret of their origin. The surprisingly simple answer – low oxygen levels – could change the way we breed plants.

The sex life of corn has gotten a lot of prurient attention over the years. By 5,000 B.C., agriculturalists in the Americas were already producing the first hybrid corn varieties by cross-pollinating plants to generate larger plants or colored kernels.

Today, hybrid seed production in corn is a multibillion-dollar industry, and crossbreeding is fundamental to the production of most other species as well. But despite plant reproduction's central role in agribusiness, researchers have never answered a basic question: Where do plant sex cells come from?

The answer, according to Stanford biology Professor Virginia Walbot and graduate student Timothy Kelliher, is surprisingly simple. In a set of elegant experiments – Walbot prides herself on "thinking of experiments you can do with basically no money" – the researchers demonstrated that low oxygen levels deep inside the developing flowers are all that is needed to trigger the formation of sex cells.
The discovery isn't only of academic interest.

"Controlling plant reproduction is fairly fundamental to modern agriculture," Walbot said.
In a corn industry that still detassels seed corn by hand as a way of controlling who fertilizes whom, a technique that switches sex cell production on or off could allow for dramatically increased control over plant crossbreeding.

The research paper appeared recently in the journal Science.

When two flowers love each other very much

All flowering plants produce pollen within structures called anthers, which in corn grow from the distinctive cluster of male flowers we know as the tassel. But before these anthers mature, they are arranged in a clover shape deep within the plant. The central cells within each of these clover-like lobes will turn into sex cells and, eventually, pollen.

The mechanism behind this development was unknown in plants. In animals, surrounding cells signal the germ line to begin forming from a single "founder cell." Walbot and Kelliher were leaning toward this view, having identified two promising signaling molecules, MAC1 and MSCA1. Plants that lacked the protein MAC1 developed too many germ cells. Plants that lacked MSCA1 had none at all.

Clearly, MAC1 was important for organizing the non-sexual cells around germ cells, while MSCA1 was necessary for cells to develop into sex cells. But the connection between the two, and what initially led to their expression, remained unclear.

A role for redox

Although most researchers assumed that, as in animals, sex cells were developing from a special set of cells with a predetermined predilection for the role, Walbot and Kelliher saw two clues that implied otherwise.

First, the physical arrangement of the sex cells didn't point to the existence of a single "founder." In fact, it suggested a scenario where "your position as a cell mattered more than who your parents were," Kelliher said.

Second, the way the MSCA1 enzyme operated suggested that oxygen levels might play a role in the signaling process.

The environment inside a plant can be either "oxidizing" – where oxygen is plentiful, and oxidation is favored – or "reducing" – where oxidation is prevented, usually by a lack of reactive oxygen, and the opposite process of reduction is favored. MSCA1 happened to send its signal through reduction – meaning that different oxygen levels might have different developmental effects.

To test the theory, the researchers inserted a probe deep into the immature anther tissue of corn. What they found was telling: unusually low oxygen levels – likely a side effect of the rapidly growing anthers' metabolic activity – at the precise time that cells were beginning to turn into sex cells.

Corn hose

To see if low oxygen alone was responsible for sex cell development, the researchers threaded a plastic hose into the developing anther and piped in mixtures of gases.

High concentrations of oxygen drastically decreased the number of sex cells. High concentrations of nitrogen gas, which is inert and provides a reducing environment, increased sex cell formation.

"It was a remarkably easy experiment," said Walbot. "We had the initial results in two days."

The researchers showed that low oxygen levels could even cause cells outside the anther lobes – which would never normally produce pollen – to develop into sex cells.

All together, Walbot explained, the evidence suggests that naturally occurring variations in oxygen levels inside the growing anther causes the central cells to become hypoxic first: "The cells that are most hypoxic then get to throw the switch."

Once oxygen levels drop below a certain threshold, MSCA1 is finally able to go to work and reduce its target, causing central cells to become sex cells. These cells then release MAC1, which in turn ensures that the outside cells don't become germline.

It's an inside-out differentiation pattern, utterly unlike what animal germlines do – which may explain why it took so long to be discovered.

"The plant takes advantage of its own structure to create this developmental signal," said Kelliher. "And then any cell can create the next generation as long as it's in the right place – you don't have to be specially designated. It's kind of a romantic idea."

Children of the corn research

Keeping a close watch over this entire plant fertility process is crucial for the hybrid seed industry. Fields are usually planted with two varieties of seed corn that are going to be crossbred. In order to keep plants from fertilizing themselves – which results in inferior-quality plants – all of the tassels of one species need to be removed.

This is an enormous task that requires specialized detasseling machines, followed up by people who check for plants that were missed.

"Currently they remove the tassels on 1 million acres of corn each year, at 20,000 plants per acre," said Walbot. "That's billions of hand-detasseled plants."

Sterile varieties of corn have been developed that don't require detasseling, but self-perpetuating versions have proven difficult to perfect. A low-oxygen sterilization method could make automated hybridization much simpler, allowing it to be applied to a large number of varieties.

"We leave those applications to industry," said Walbot. But the effects of the research could be wide-ranging. Assuming that the findings hold true for all flowering plants, as a number of research groups are now seeking to confirm, the discovery could open up a new level of fertility control for a huge array of crops.

Further Information
Access to this exclusive content is for Technology Networks Premium members only.

Join Technology Networks Premium for free access to:

  • Exclusive articles
  • Presentations from international conferences
  • Over 2,600+ scientific posters on ePosters
  • More Than 3,800+ scientific videos on LabTube
  • 35 community eNewsletters

Sign In

Forgotten your details? Click Here
If you are not a member you can join here

*Please note: By logging into you agree to accept the use of cookies. To find out more about the cookies we use and how to delete them, see our privacy policy.

Related Content

How Cell Growth Triggers Cell Division
Researchers in Jan Skotheim's lab have discovered a previously unknown mechanism that controls how large cells grow, an insight that could one day provide insight into attacking diseases such as cancer.
Wednesday, October 07, 2015
Tension Helps Heart Cells Develop Normally in the Lab
Stanford engineers have uncovered the important role tension plays in growing heart cells out of the body.
Monday, October 05, 2015
Drug Disarms Deadly C. difficile Bacteria Without Destroying Healthy Gut Flora
A drug that blocks the intestinal pathogen without killing resident, beneficial microbes may prove superior to antibiotics, currently the front-line treatment for the infection.
Friday, September 25, 2015
Virus Re-Engineered to Deliver Targeted Therapies
Researchers stripped a virus of its infectious machinery and turned its benign core into a delivery vehicle that can target sick cells while leaving healthy tissue alone.
Thursday, September 24, 2015
Combination Drug Therapy Shrinks Pancreatic Tumors In Mice
Two drugs that affect the structure and function of DNA have been found to block the growth of pancreatic tumor cells in mice, researchers hope the drugs can soon be tested in humans with the disease.
Thursday, September 24, 2015
Delivering Missing Protein Heals Damaged Hearts in Animals
Researchers have discovered that a particular protein, Fstl1, plays a key role in regenerating dead heart-muscle cells.
Tuesday, September 22, 2015
Key Mechanism in Gene Expression Discovered
RNA polymerase II makes life possible by expressing genes. Now, a team of Stanford biologists, chemists and applied physicists has observed it at work in real time.
Thursday, September 17, 2015
Drug Prevents Type 1 Diabetes In Mice
A compound that blocks the synthesis of hyaluronan, a substance generally found in in all body tissue, protected mice from getting Type 1 diabetes. The compound is already approved in Europe and Asia for the treatment of gallbladder disease.
Wednesday, September 16, 2015
New Method for Producing Vital Cancer Drug
Stanford scientists produced a common cancer drug – previously only available from an endangered plant – in a common laboratory plant.
Tuesday, September 15, 2015
Scientists Home In On Origin Of Human, Chimpanzee Facial Differences
A study of species-specific regulation of gene expression in chimps and humans has identified regions important in human facial development and variation.
Monday, September 14, 2015
X-ray Laser Experiment Could Help in Designing Drugs for Brain Disorders
Scientists found that when two protein structures in the brain join up, they act as an amplifier for a slight increase in calcium concentration, triggering a gunshot-like release of neurotransmitters from one neuron to another.
Monday, August 24, 2015
Researchers Develop qPCR Prognosis Test for NSCLC Patients
A nine-gene molecular prognostic index (MPI) for patients with early-stage non-small cell lung cancer (NSCLC) was able to provide accurate survival stratification and could potentially inform the use of adjuvant therapy in patients struggling with the disease.
Thursday, August 20, 2015
Scientists Genetically Modify Yeast to Produce Opioids
The technique could improve access to medicines in impoverished nations, and later be used to develop treatments for other diseases.
Monday, August 17, 2015
Identifying Defective Heart Genes
A new technique could eventually enable doctors to diagnose genetic heart diseases by rapidly scanning more than 85 genes known to cause cardiac anomalies.
Thursday, August 13, 2015
Elusive Liver Stem Cell Identified in Mice by Researchers
Researchers have found a previously unknown population of cells in mice that function as liver stem cells. The finding could aid drug testing and increase understanding of liver biology and disease.
Friday, August 07, 2015
Scientific News
Genetic Defences of Bacteria Don’t Aid Antibiotic Resistance
Genetic responses to the stresses caused by antibiotics don’t help bacteria to evolve a resistance to the medications, according to a new study by Oxford University researchers.
Detecting HIV Diagnostic Antibodies with DNA Nanomachines
New research may revolutionize the slow, cumbersome and expensive process of detecting the antibodies that can help with the diagnosis of infectious and auto-immune diseases such as rheumatoid arthritis and HIV.
Snapshot Turns T Cell Immunology on its Head
New research may have implications for 1 diabetes sufferers.
Tolerant Immune System Increases Cancer Risk
Researchers have found that individuals with high immunoCRIT ratios may have an increased risk of developing certain cancers.
Developing a Gel that Mimics Human Breast for Cancer Research
Scientists at the Universities of Manchester and Nottingham have been funded to develop a gel that will match many of the biological structures of human breast tissue, to advance cancer research and reduce animal testing.
Cell's Waste Disposal System Regulates Body Clock Proteins
New way to identify interacting proteins could identify potential drug targets.
New Approach to Treating Heparin-induced Blood Disorder
A potential treatment for a serious clotting condition that can strike patients who receive heparin to treat or prevent blood clots may lie within reach by elucidating the structure of the protein complex at its root.
Horse Illness Shares Signs of Human Disease
Horses with a rare nerve condition have similar signs of disease as people with conditions such as Alzheimer’s, a study has found.
How a Molecular Motor Untangles Protein
Diseases such as Alzheimer’s, Parkinson’s and prion diseases, all involve “tangled” proteins.
Compound Doubles Up On Cancer Detection
Researchers have found that tagging a pair of markers found almost exclusively on a common brain cancer yields a cancer signal that is both more obvious and more specific to cancer.
Scroll Up
Scroll Down
Skyscraper Banner

Skyscraper Banner
Go to LabTube
Go to eposters
Access to the latest scientific news
Exclusive articles
Upload and share your posters on ePosters
Latest presentations and webinars
View a library of 1,800+ scientific and medical posters
2,600+ scientific and medical posters
A library of 2,500+ scientific videos on LabTube
3,800+ scientific videos