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Showing posts with label Nature. Show all posts
Showing posts with label Nature. Show all posts

Sunday, 16 February 2020

Mysteries of plant reproduction revealed by real-time imagery

Imaging of a Ladies' Arabette, with its pollen seeds highlighted by green fluorescence. | Valuchova, Mikulkova et al.

A new technique based on microscopy has been used by researchers to observe stages of reproduction of flowering plants never described before. The results obtained reveal crucial information which will help us to understand the different processes involved.

In flowering plants, reproduction takes place in two organs: the anther, which is the male reproductive system and the place where pollen is formed, as well as in the ovary, the female reproductive organ containing the waiting eggs. to be fertilized by contact with pollen.

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Also called germ cells, pollen grains and eggs multiply during meiosis and mitosis, which are cell division processes. After fertilization, the resulting cell will develop into a plant.

Although dissection of flowering plants under the microscope and the study of abnormalities caused by gene mutations have so far been the most widely used techniques to study the different stages of germ cell division and reproduction, they do not provide any information on the exact moment when this occurs. Questions that a team of researchers wanted to answer using real-time imagery.

High resolution three-dimensional images

"Real-time imaging has been instrumental in researching root growth and development, but imaging cellular processes within the flower is technically much more difficult," said the co-author of the Sona Valuchova study, from Masaryk University, in the Czech Republic. "It is necessary to develop methods of imaging organs or plants in their entirety".

To get to the end, Valuchova and her colleagues used light-sheet fluorescence microscopy (LSFM), where plant samples trapped in agar were passed through a thin plane of laser light. A detector then produced data to obtain high-resolution three-dimensional images, thus making it possible, (thanks to the detailed structures of the flower imaged) to follow the fate of an individual germ cell from the inside.

Maximum intensity projection of a cut flower from the bud, at the height indicated above. The second line of images shows anthers in more detail. Credits: Sona Valuchova et al.

Having shown that LSFM could provide high-resolution images of flowers, the team's next goal was to establish that it could detect specific events in reproduction. To achieve this, they used flowers that had been engineered to have fluorescent labels on key molecules involved in meiosis and mitosis. They were able to capture the entire process of meiosis in male germ cells by detecting changes in the amount and location of a molecule called ASY1 every hour for four days.

The team went on to show that live imaging could be successfully used to study plant hormone levels during different stages of flower development and to watch the movement of chromosomes across the cell during cell division.

Imaging of a 0.5 mm flower bud expressing the protein ASY1 (here in green), seen from eight different angles. Credits: Sona Valuchova et al.

Detailed observation of germ cells during cell division

The last objective of their research was to observe the production of female germ cells during meiosis. This process has often been overlooked in the past, as these are rarer than their male counterparts. In addition, they have a strong resemblance to other cells, making it difficult to trace them during division.

The team had to set up another method to be able to follow meiosis of the eggs. They carefully dissected the bud, revealing the eggs. These were then passed every ten minutes (for 24 hours) under the laser to obtain a 3D film. The researchers were thus able to visualize the two stages of meiosis in female germ cells, as well as determine their duration.

"This work demonstrates the power of light-layer microscopy to provide new information on plant reproduction, which could not previously be studied by other types of microscopy," said Karel Riha, researcher and director of the Masaryk University Institute of Technology. "Our success in developing a real-time imaging protocol for female meiosis represents major technical progress in plant cell biology."


Imaging plant germline differentiation within Arabidopsis flowers by light sheet microscopy

Sona Valuchova

DOI: 10.7554/eLife.52546

Friday, 31 January 2020

The ocean has become so acidic that it literally dissolves the crab shells ...

A new study reveals an alarming fact: the acidity of the Pacific Ocean has become so great that it dissolves the shells of crab larvae. This phenomenon is happening much earlier than researchers feared, demonstrating once again the critical state of our oceans and its potential consequences on the entire chain of life.

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This study was conducted by an international team of researchers and funded by the National Oceanic and Atmospheric Administration (NOAA). NOAA studies in particular the acidification of the oceans and the impact of pH changes on the coasts.

The acidity of the water only increases

You should know that the world's oceans absorb about 30% of the carbon dioxide released into the atmosphere. This means that as the levels of CO2 in the atmosphere have increased, so too have the levels of CO2 in seawater, which in turn leads to an increase in the acidity of the water.

Now, researchers have found that ocean acidification along the west coast of the United States is increasing faster than that seen in the rest of the globe . This is particularly evident in coastal regions (up to 200 meters deep), which have a lower buffer capacity while at the same time providing substantial habitats for ecologically and economically important species. It is for this reason that the researchers focused on this area during their study, studying a species emblematic of the region: the sleeping crab.

And, according to the results, the acidity of the water has become so high that it goes so far as to dissolve the shells of newly hatched sleeper crabs.

Crabs will weaken… faster than expected

Researchers have found that the lower pH levels in their habitat affect the larvae by dissolving parts of their shells and damaging their sensory organs (which they typically use to navigate their environment).

This particular fact is already very worrying. However, scientists have been more alerted to the prematurity of this phenomenon. Indeed, the acidity of the water should not affect the crabs so quickly.  "We have discovered dissolution effects on crab larvae that are not expected to occur until much later in the century," said Richard Feely, study co-author and lead NOAA scientist.

This can only generate many problems for crabs: an inability to defend themselves against predators, poor buoyancy and loss of orientation due to the loss of their sensory organs, and difficulty moving around. Indeed, the consequences of the dissolution of the crab larvae are absolutely dramatic for their development towards adulthood.

“If these larval crabs need to divert energy to repair their exoskeletons, and are smaller, as a result, the percentage that makes it to adulthood will be at best variable, and likely go down in the long-term,” added Bednarsek to NOAA. “[...] if the crabs are affected already, we really need to make sure we start to pay much more attention to various components of the food chain before it is too late.”

This infographic shows the location of the crab larvae sampling, examples of ocean acidification impacts, and photos of a larval crab (left) and an adult crab (right). Credits: Nina Bednarsek / SSCWRP.

Ocean acidification is a danger to all

This discovery not only has an impact on crabs and the Pacific ecosystem: it could also affect the economies of cities in the Pacific Northwest, which fish and sell crustaceans (in these areas, the sleeper crab is an essential part of commercial fishing).

Unfortunately, that is not all. Becoming aware of these lesions of crabs is just one of the many symptoms demonstrating the critical state of our oceans. Ocean acidification is now threatening the entire food chain (as all species are interconnected and vital). "If the crabs are already affected, we really need to make sure that we pay much more attention to the different components of the food chain before it's too late," said Bednarsek.

In addition, as the ocean becomes more acidic because it absorbs more carbon dioxide from the atmosphere, this lowers the pH of the water. Then, the fact that the pH is lower, according to NOAA, modifies the ribs by releasing an excess of nutrients which can give rise to overgrowth of algae and thus participate in the increase in temperature and salinity of the water. Consequently, crustaceans and corals have a harder time forming a solid shell because they depend on carbonate ions, which are less abundant in more acidic waters. In the front line of sight, there are therefore not only crabs, but also oysters, clams and plankton, which all need the same carbonate ions to strengthen.

Ultimately, therefore, the entire ocean cycle is considerably weakened. NOAA stresses that it is absolutely vital to reduce our overall carbon footprint to decrease the carbon dioxide absorbed by the sea and try to at least slow the increase in ocean acidification.


Exoskeleton dissolution with mechanoreceptor damage in larval Dungeness crab related to severity of present-day ocean acidification vertical gradients

Bednaršek et al - Science of The Total Environment,

doi: 10.1016/j.scitotenv.2020.136610.

Wednesday, 22 January 2020

This strange organism from the depth could hold secrets about the origins of complex life on Earth

Illustration of a eukaryotic cell. They evolved from single-celled organisms about 2 billion years ago. | Shutterstock

A mysterious microbe discovered in the depths of the Pacific Ocean could hold the secrets of the evolution of the first muticellular life forms. Indeed, according to a new study, the little “tentacle organism” could tell us about what allowed life to become more complex during the early stages of evolution.

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Long before complex living things existed, the world was home to simple single-celled organisms, archaea and bacteria. Between 2 and 1.8 billion years ago, these microorganisms began to evolve, leading to the emergence of more complex life forms, called eukaryotes.

The field of eukaryotes today includes humans, animals, plants and fungi. But this incredible evolution from aquatic life to life out of the water, then to walking - and for more advanced beings, thought and feeling, is still poorly understood by scientists.

The Asgard archaea, potential ancestors of eukaryotes

In a previous study, biologists hypothesized that an archival group called Asgard archaea (the archaea of ​​Asgård) regrouped the much sought-after ancestors of eukaryotes because they contain genes similar to their complex counterparts.

To analyze what these microbes looked like and how this transition could have happened, a group of Japanese researchers then spent a decade collecting and analyzing the mud from the bottom of Omine Ridge, off the coast of Japan. The results of the study were published on January 15 in the journal Nature.

The team stored the mud samples (and the microorganisms found there) in a special bioreactor, in a laboratory environment that mimics the conditions of the deep sea in which they were found.

Years later, they began to isolate the microorganisms in samples. The researchers' original goal was to find methane-consuming microbes that might be able to clean up the wastewater, according to the New York Times . But when they discovered that their samples contained an unknown strain of Asgard archaea, they decided to analyze it and grow it in the laboratory.

These images obtained by scanning electron microscopy show (A) an isolated archaea, (B) several cells developing together in the laboratory archaea, and (C&D) with tentacle-like protrusions, which develop towards the end of their growth. Credits: Japan Agency for Marine and Land Science and Technology (JAMSTEC)

Prometheoarchaeum syntrophicum , a new strain of Asgard archaea

They named the newly found strain of Asgard archaea “ Prometheoarchaeum syntrophicum “, after the Greek god Prometheus, who is said to have created humans out of mud, according to mythology.

The researchers found that these archaea were grown relatively slowly, doubling only every 14 to 25 days. Their analysis then confirmed that P. syntrophicum had a large number of genes similar to those of eukaryotes. In fact, these genes held the instructions to create certain proteins present inside these microbes. However, as expected, proteins did not create organelle-like structures like those found inside eukaryotes.

They also found that the microbes had long, branched, tentacle-like protrusions on the outside that could be used to catch passing bacteria. Indeed, the team discovered that microbes tended to stick to other bacteria in the petri dishes.

An elegant hypothesis explaining the changes in P. syntrophicum

The authors offer an interesting hypothesis for what happened in these ancient waters, which they explain in a recently published video (available at the end of the article): about 2.7 billion years ago, oxygen a started to accumulate on Earth. But having lived so long in a world without oxygen, this element would prove to be toxic for P. syntrophicum .

So P. syntrophicum may have developed a new adaptation: a way of forming bonds with oxygen-tolerant bacteria. These bacteria would have provided P. syntrophicum with the vitamins and compounds necessary to survive, while in turn feeding on archaeal waste.

As oxygen levels increased even more, P. syntrophicum could have become more aggressive, uprooting passing bacteria with its long tentacle-like structures and integrating them. Inside P. syntrophicum , this bacterium would eventually have evolved into an energy-producing organelle, the key to eukaryotic survival: the mitochondria.

The success of the team in the culture of Prometheoarchaeum , after efforts spanning more than a decade, “represents a huge breakthrough for microbiology”, writen by an accompanying editorial Christa Schleper and Filipa L. Sousa, two researchers from the University of Vienna, who did not participate in the study. " It opens the way to the use of molecular and imaging techniques to further elucidate the metabolism of Promethéoarché and the role of eukaryotic signature proteins in biology of Archean cells " they added.


Isolation of an archaeon at the prokaryote–eukaryote interface

Hiroyuki Imachi, Masaru K. Nobu, Nozomi Nakahara, Yuki Morono, Miyuki Ogawara, Yoshihiro Takaki, Yoshinori Takano, Katsuyuki Uematsu, Tetsuro Ikuta, Motoo Ito, Yohei Matsui, Masayuki Miyazaki, Kazuyoshi Murata, Yumi Saito, Sanae Sakai, Chihong Song, Eiji Tasumi, Yuko Yamanaka, Takashi Yamaguchi, Yoichi Kamagata, Hideyuki Tamaki & Ken Takai

Nature volume 577, pages519–525(2020)

Wednesday, 18 December 2019

Extreme heat waves are linked to a newly discovered atmospheric model

Researchers have discovered a new link between a pattern of fluctuations of a particular type of wave in jet streams (Rossby waves) and paralyzing heat waves, which strike several regions of the world simultaneously.

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They are called "Rossby waves" (or planetary waves), an atmospheric and oceanic phenomenon in which giant meanders distort the flow of currents in an undulatory model. It does not only occur on Earth, but also on other planets or stars (including the Sun). Rossby waves are particularly known for influencing the global climate.

Thanks to a recent study, the extent of this influence is becoming clearer. By analyzing the results, researchers have discovered that when certain amplified wavelengths take shape in jet streams - rapidly circulating air streams that pass through the atmosphere at high altitudes - the phenomenon is linked to the emergence simultaneous heat waves that devastate certain regions. The results were published in the journal Nature Climate Change.

Most affected regions: main agricultural producers

" We have seen a 20- fold increase in the risk of simultaneous heat waves in major agricultural regions when these global wind regimes are in place, " said Kai Kornhuber, a researcher in Earth systems at the University. Columbia. In other words, when the phenomenon occurs, it is mainly the main food producing regions that are affected.

Development of a Rossby wave along the thermal ribbon (or front). Credits: Wikipedia

Kornhuber and his team analyzed climate data from 1979 to 2018 and found that when two particular wavelengths of circonglobal Rossby waves - called wave-5 and wave-7 - scattered in the jet stream of the 'northern hemisphere, they channeled warm subtropical air into regions of North America, Europe and Asia.

Temperature spikes that can persist for weeks

Hot air produces temperature spikes that can persist for weeks: extreme weather events that threaten people and global food security, due to their widespread impact on crops.

" Two weeks or more per summer spent in wave 5 or wave 7 are associated with 4% reductions in agricultural production on average, with regional decreases of up to 11%,  " write the researchers. in the document.

And the scary effects don't stop there… Crop losses lead to higher food prices, and although researchers recognize that these prices can be affected by a host of other factors, they nevertheless believe that the impacts on the harvest due to the effects of Rossby are significant.

According to the researchers, these wave patterns appeared five times during the study period (1983, 2003, 2006, 2012 and 2018), but although it is not yet known how climate change could affect the phenomenon, the impact of these major disturbances on a mode already warming is rather worrying.

"Even if the frequency or size of the (Rossby) waves does not change, the related heat extremes will become more severe as the atmosphere as a whole heats up, " says Kornhuber. " Until now, this has only been an under-explored vulnerability of the food system ."

However, the team recognizes that more research is needed to determine how future climate projections would be affected by this discovery. Until this is done, we will not know the exact impact of Rossby waves on the world of tomorrow.


Amplified Rossby waves enhance risk of concurrent heatwaves in major breadbasket regions

Kai Kornhuber, Dim Coumou, Elisabeth Vogel, Corey Lesk, Jonathan F. Donges, Jascha Lehmann & Radley M. Horton -

Nature Climate Change (2019)

Monday, 4 November 2019

In contact with rain, plants activate a "panic" reaction

Although, as for animals, water is the basic element of life for plants, it does not mean that they appreciate the contact with water. This is revealed in a recent study that examined the behavior of plants subjected to water sprays. In contact with the droplets, a "panic" reaction is activated, initiating multiple physiological and genetic modifications so that the plant protects itself (and its neighbors) from the spread of pathogens carried by the drops of water.

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Moisture is the main means of spreading disease among vegetation, even more than temperature. The longer a leaf is wet, the more likely it is that a pathogen will move into it.

" When a drop of rain splashes a leaf, tiny droplets of water ricochet in all directions, " says plant biochemist Harvey Millar of the University of Western Australia. " These droplets may contain bacteria, viruses or fungal spores. A single droplet can transmit them up to 10 meters away, to the surrounding plants .

A rapid modification of gene expression in contact with water

By mimicking the rain with a vaporizer, an international team of researchers observed a rapid domino effect of microscopic plant changes, initiated by a powerful protein called Myc2. During the first 10 minutes of contact with water, more than 700 genes from the plants reacted, and most of these genes continued to increase their expression for about 15 minutes, thus modifying proteins, transcription and the hormonal balance of the plant, before returning to normal.

After simple contact with water, the authors report that these plants immediately accumulated signaling compounds such as calcium, activating membrane responses to touch and causing transcriptional changes at the genome level. However, even if these changes were only momentary, repeated contact eventually led to stunting and delayed flowering. The results were published in the journal PNAS.

In contact with water, the expression of several genes (green arrows) is modified under the action of Myc2 to protect the plant. Credits: Alex Van Moerkercke et al. 2019

" When Myc2 is activated, thousands of genes come into action to prepare the plant's defenses. These warning signals propagate from sheet to sheet and induce a range of protective effects, "explains Millar. In total, no less than 20 protein-related genes were found to be directly targeted and regulated by Myc2 after water spraying. In addition, the same signals that these plants used to spread information among their leaves were also used to communicate with the surrounding vegetation.

A communication of the danger to the surrounding plants

According to the authors, one of the many chemicals generated in response to water droplets is jasmonic acid, which regulates many physiological processes involved in plant growth and stress management. In addition, when jasmonate chemicals are suspended in the air, they can also inform other plants of what is happening.

Jasmonic acid is a chemical compound synthesized by plants in response to stress and different stimuli. It generates a number of physiological changes. These graphs show the increase in the level of jasmonic acid synthesized by the plant during the attack of an insect (red). Credits: Ying-Bo Mao et al. 2017

If the defense mechanisms of a plant's neighbors are activated, they are less likely to spread disease, so it is in their interest that plants pass on the warning to nearby plants, " says Millar. Earlier this month, another article revealed that when plants are attacked, they develop a universal language to warn others of dangerous imminent threats.


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