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Biology in Action - a blog on new developments in wider biology

(7) The nervous system of plants

Plants can communicate ‘danger’. They can detect the pressure of a caterpillar on one of its leaves and can respond defensively. Within minutes, an undamaged leaf can respond to the fate of a distant damaged leaf. The signals they use are similar to those in an animal’s system.
Scientists have been working on a mustard plant (Aribidopsis) to determine the effect of gravity on its growth. Aribidopsis is a popular plant for genetical research because of its small size, short life cycle, and its reproduction through self-pollination.
 
To carry out their work they developed a molecular sensor that could detect changes in calcium levels in the plant cells. This sensor glows as calcium levels increase. The above image shows this.  They noticed that the levels of calcium (i.e. the brightness) was greatest in areas where the plant was damaged.
 
When they cut the plant they saw a glow that became brighter at the point of the damage. This then dimmed but the brightness appeared and disappeared further away from the damaged area into other parts of the plants as the wave of calcium increase travelled. The signal causes the release of defense hormones in other parts of the plant as the signal reaches them. All this takes just a few minutes.
 
This communication is carried out using the amino acid glutamate.
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Any damage to plant cells results in the release of glutamate activating receptor that triggers the increase of a calcium-based signal that moves through the plant using the plant’s vascular system (xylem and phloem).  
 
This is a remarkably similar process to how information is transmitted in animals. Animal nerve cells also communicate through the use of the neurotransmitter glutamate.  When it is released in a nerve cell it sends a wave of calcium onto other nerve cells to enable long-distance communication.
 
You can see a fascinating
video that shows this process taking place.
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(6) Cyclops

Cyclops


Cyclops is, like Daphnia that I looked at in the last blog, a beautiful minute (0.5 – 2 mm) freshwater crustacean. For pretty obvious reasons, it is named after the single-eyed giant of Greek mythology (as was the character in the X-Men series!).

Greek Cyclops


Like
Hydra and Daphnia they were among the first fascinating objects I saw down my microscope 60 odd years ago. They still hold their fascination.

They feed on other plankton, and can be found in stagnant bodies of freshwater, under the ice in
frozen lakes and also in hot climates such as sub-Saharan Africa, India and the Yemen. They are, in turn, fed upon by small fish and other aquatic animals.

Some species of
Cyclops are medically important in that they can be the intermediate hosts of the guinea worm, Dracunculus medinensis, a parasite that causes guinea-worm disease or dracunculiasis. The disease is transmitted to humans when they drink water containing infected Cyclops.

Cyclops moves with a characteristic jerky movement.

The main visible characteristic of
Cyclops is, as expected, a single eye that can be red or black.

Cyclops eye


The females carry the typical egg sacks. They can reproduce without fertilisation for many generations, but when conditions become difficult, for example when the habitat starts to dry up, a generation of both male and female
Cyclops can occur produces fertilized eggs. You can even see the eggs hatching.

Another captivating organism.

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(5) Daphnia - water fleas

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I am not sure what this beautiful crustacean has done to deserve the pejorative alternative name of 'water flea'. Daphnia are minute (0.2 - 0.5 mm) crustaceans that live in freshwater lakes, ponds and streams. Their transparent carapace (outer shell) allow us to see the compound eye, antennae, beating heart (180 beats/minute), blood cells. eggs and intestine.
 
This transparency has made them ideal
test specimens for looking at the effect of alcohol, caffeine, nicotine or adrenaline on increasing heart rate.
 
By the way, they can also
juggle.
 
Daphnia reproduce by the asexual process of parthenogenesis (eggs are developed without fertilization) with the eggs stored in a brood pouch before being released to become fully grown adults in two weeks. However, there are males and females an sexual reproduction can occur, allowing greater variation in offspring through genetic recombination. Adults live from 1 - 12 months depending upon the local temperature.
 
Daphnia are a very important part of the aquatic food chain. They feed on bacteria, yeast and algae, while In nature they are food for tadpoles, newts, aquatic insects and many types of fish.
 
Unfortunately, most people know Daphnia as packets of dried fish food, although many cultivate their own
live cultures. You can also buy live cultures on-line.
 
Armed with a low-power microscope or hand lens, you will find these are fascinating creatures to study – before you give them to your fish to eat!
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(4) - Rotifers

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Freshwater ponds, streams and lakes are full of the most amazing microscopic organisms. Some are beautiful, while others are the stuff of nightmares writ small. Rotifers fall into the second category.
They are 0.1 - 2 mm long animals that feed on bacteria, algae and smaller protozoans by pulling them into their bodies by means of ‘coronal cilia’ - https://www.youtube.com/watch?v=PALgTXQOqQo. You can see a rotifer ingesting bacteria at https://www.youtube.com/watch?v=gGk7qJ9y3Ko

There Is another beautiful video (it is possible to be both beautiful and hair-raising!) at https://www.youtube.com/watch?v=Fb0t18Js6rU and one that shows a rotifer with a ‘baby’ bud attached at https://www.youtube.com/watch?v=XVxsTYuEyy8 - you can see the photosensitive bright red ‘eyespots’. (Above image taken from this video).

As someone involved in the commercial growth of microalgae, rotifers are a significant foe in that they can infect microalgal cultures and act as ‘grazers’ – decimating the culture.
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(3) - Hydra an 'immortal' organism

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When I bought my first microscope 60 years ago (£4 from a local pawnbroker!) it was because I had seen photographs of Hydra - fascinating small organisms living in fresh water (https://www.youtube.com/watch?v=qR4SqkbPycY).

Hydra consist of a hollow tubular body up to 10 mm long that has a basal disc it uses to attach itself to leaves or stones in ponds or streams. At the front end it has a mouth that can expand to swallow its prey (freshwater crustacea such as Cyclops or Daphnia (see later blogs). It catches these using tentacles that are covered with stinging cells (cnidocytes) that fire darts into their prey to paralyse them. Hydra also contain symbiotic microalgae, hence the typically green colour.
There are many videos available that show different aspects of the life of hydra:


I challenge anyone to watch these videos and not want to change careers and become a microbiologist.
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(2) - 50 million crabs on the move

Baby crabs
One of great natural wonders - once a year, 50,000,000 red crabs (Gecarcoidea natalis) travel across Christmas Island (off the northwest coast of Australia) at the start of the wet season to go to the seaside and lay their eggs.

There is an amazing video showing this at
https://www.youtube.com/watch?v=t8w45olilG8
Islanders do everything they can to protect the crabs during their migration to the sea https://www.lifegate.com/people/news/migration-red-crabs-christmas-island including building bridges and underground tunnels to enable them to cross busy roads. At the peak of the event some roads are closed and traffic is diverted.
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David Border - Consultant Microbiologist

Wider biology 

David Border - Consultant Microbiologist