Hexbyte Glen Cove Realtime imaging of female gamete formation in plants thumbnail

Hexbyte Glen Cove Realtime imaging of female gamete formation in plants

Hexbyte Glen Cove

Development of the female gamete was observed over 20 hours, clearly showing the division of the nuclei and formation of the egg, central and synergid cells. Credit: Issey Takahashi

Scientists from Nagoya University, Yokohama City University and Chubu University have developed a system which enables the live imaging of the formation of the female gamete in plants.

In flowering plants, the sperm cell and egg cell meet and fertilization takes place in the flower. While are made in the pollen, are made in the ovule, the structure that becomes the seed. However, as the ovule is buried deep within the pistil, it has thus far been impossible to observe the formation of the egg cell in living plants.

The team, led by Dr. Daisuke Kurihara and Dr. Tetsuya Higashiyama of Nagoya University Institute of Transformative Bio-Molecules (WPI-ITbM), Dr. Daichi Susaki of Yokohama City University Kihara Institute for Biological Research and Dr. Takamasa Suzuki of Chubu University College of Bioscience and Biotechnology, using the ovule culturing technology that they had developed previously, succeeded in capturing images of the egg cell being formed inside the ovule. On top of that, they were able to isolate the egg cell and its neighboring , and by analyzing the genes expressed in these few cells, identify how the cells adjoining the egg cell determine its fate.

Living things which carry out sexual reproduction produce offspring via a fertilization process involving male and female gametes. In animals, the female gamete (the egg) is produced by meiosis, a type of cell division that halves the number of chromosomes present in the cell. However, the process in flowering plants is rather more lengthy. Following meiosis, karyomitosis (nuclear division) takes place three times within the cell, resulting in the production of a single cell with eight . This cell then divides, producing cells with a variety of different roles including two gametes, the egg cell and central cell, and the synergid cells. However, it was not yet understood precisely how the two female gametes were produced among the seven new cells that result from this process of division.

Using an ovule culturing method that they had developed previously, the research team attempted the observation in real time of the formation of the female gamete in Arabidopsis thaliana. They saw that when the first nuclear division takes place, the resulting two nuclei go to the opposite ends of the cell. Dividing again into four, the nuclei then line up along the edge of the cell. Finally, dividing again into eight, the plasma membranes are constructed around the nuclei, forming the cells which are attached to the two gametes (the egg cell and central cell). Having observed 157 cases of this division, they found that the nuclei close to where the pollen tube penetrates would become the nuclei of the synergid, egg and central cells, demonstrating that the position of the nuclei within the cell has a strong correlation with cell fate.

Continuing, in order to find out when the various cells’ fates are determined, they analyzed the time at which expression of the specific transcription factor myb98, important for the differentiation and function of the synergid cells, commenced. They found that myb98 begins to be expressed very shortly after the nuclei divide into 8 and are enclosed by the plasma membranes. Given that the specific transcription factor for the egg cell can also be found in the egg cell at the same early stage, it can be considered that cell fate is determined immediately after the formation of the plasma membranes, or possibly even earlier.

The time at which cell fate is determined is significant because it gives us an insight into how plants remain adaptable to environmental conditions by flexibly changing cell fate and thus ensuring the survival of crucial cells such as gametes.

Looking to the future, the research team’s focus will be on discovering how the cell fate change is accomplished, and explaining its . Once the molecular mechanism has been analyzed, it is expected that this field of research will contribute to the development of methods to increase plant fertilization rates and environmental resistance, offering the prospect of solving key issues in food supply that affect millions of people around the world.

More information:
Daichi Susaki et al, Dynamics of the cell fate specifications during female gametophyte development in Arabidopsis, PLOS Biology (2021). DOI: 10.1371/journal.pbio.3001123

Realtime imaging of female gamete formation in plants (2021, April 2)
retrieved 5 April 2021
from https://phys.org/news/2021-04-

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Hexbyte Glen Cove New imaging method views soil carbon at near-atomic scales thumbnail

Hexbyte Glen Cove New imaging method views soil carbon at near-atomic scales

Hexbyte Glen Cove

Credit: CC0 Public Domain

The Earth’s soils contain more than three times the amount of carbon than is found in the atmosphere, but the processes that bind carbon in the soil are still not well understood.

Improving such understanding may help researchers develop strategies for sequestering more carbon in soil, thereby keeping it out of the atmosphere where it combines with oxygen and acts as a greenhouse gas.

A new study describes a breakthrough method for imaging the physical and chemical interactions that sequester carbon in soil at near atomic scales, with some surprising results.

The study, “Organo-organic and Organo-mineral Interfaces in Soil at the Nanometer Scale,” was published Nov. 30 in Nature Communications.

At that resolution, the researchers showed—for the first time—that soil carbon interacts with both minerals and other forms of carbon from organic materials, such as bacterial cell walls and microbial byproducts. Previous imaging research had only pointed to layered interactions between carbon and minerals in soils.

“If there is an overlooked mechanism that can help us retain more carbon in soils, then that will help our climate,” said senior author Johannes Lehmann, the Liberty Hyde Bailey Professor in the School of Integrative Plant Science, Soil and Crop Sciences Section, in the College of Agriculture and Life Sciences. Angela Possinger Ph.D. ’19, who was a graduate student in Lehmann’s lab and is currently a postdoctoral researcher at Virginia Tech University, is the paper’s first author.

Since the resolution of the new technique is near atomic scale, the researchers are not certain what compounds they are looking at, but they suspect the carbon found in soils is likely from metabolites produced by soil microbes and from microbial cell walls. “In all likelihood, this is a microbial graveyard,” Lehmann said.

“We had an unexpected finding where we could see interfaces between different forms of carbon and not just between carbon and minerals,” Possinger said. “We could start to look at those interfaces and try to understand something about those interactions.”

The technique revealed layers of carbon around those organic interfaces. It also showed that nitrogen was an important player for facilitating the chemical interactions between both organic and mineral interfaces, Possinger said.

As a result, farmers may improve soil health and mitigate climate change through sequestration by considering the form of nitrogen in soil amendments, she said.

While pursuing her doctorate, Possinger worked for years with Cornell physicists—including co-authors Lena Kourkoutis, associate professor of applied and , and David Muller, the Samuel B. Eckert Professor of Engineering in Applied and Engineering Physics, and the co-director of the Kavli Institute at Cornell for Nanoscale Science—to help develop the multi-step method.

The researchers planned to use powerful electron microscopes to focus electron beams down to sub-atomic scales, but they found the electrons modify and damage loose and complex soil samples. As a result, they had to freeze the samples to around minus 180 degrees Celsius, which reduced the harmful effects from the beams.

“We had to develop a technique that essentially keeps the soil particles frozen throughout the process of making very thin slices to look at these tiny interfaces,” Possinger said.

The beams could then be scanned across the sample to produce images of the structure and chemistry of a sample and its complex interfaces, Kourkoutis said.

“Our physics colleagues are leading the way globally to improve our ability to look very closely into material properties,” Lehmann said. “Without such interdisciplinary collaboration, these breakthroughs are not possible.”.

The new cryogenic electron microscopy and spectroscopy technique will allow researchers to probe a whole range of interfaces between soft and hard materials, including those that play roles in the function of batteries, fuel cells and electrolyzers, Kourkoutis said.

More information:
Angela R. Possinger et al. Organo–organic and organo–mineral interfaces in soil at the nanometer scale, Nature Communications (2020). DOI: 10.1038/s41467-020-19792-9

New imaging method views soil carbon at near-at