Exosomes

Today, we are looking at some cutting-edge research in the world of plants. It may not make you a better gardener, but you’ll know more about plants than pretty much everyone else, and you may look at your plants a little differently.

Exosomes (Maximus155) CC BY-SA 3.0

Plant cells

Imagine, if you will, a tiny plant cell. Within that cell is a bubble of fluid, called a vesicle. Vesicles form naturally as plant cells eat and poop and go about their business. You can think of these bubbles as microscopic burps that stick around. Plant cells can also create vesicles on purpose. When this happens, they are called liposomes. [Keep in mind that this is an extreme oversimplification of what is actually going on, but you’ll have the basic idea.] A plant cell may have several vesicles, which cluster together into groups, called multivesicular bodies (MVB).

Vesicles

Vesicles are extremely small. They range in size from 30 to 150 nanometers (nm). A nanometer is one billionth of a meter. By comparison, plant cells range from 10 to 100 micrometers, while animal cells can be 10 to 30 micrometers. Micrometers (μm) are one millionth of a meter. A strand of human hair ranges from 17 to 181 µm.

Ergo, one human hair = 10 plant cells = 300 vesicles

What do vesicles do?

Plant cells use vesicles to move materials around, process proteins, maintain buoyancy, and all sorts of other things that we are only now learning about, though scientists have known about the existence of vesicles for a while now. What we didn’t know, until very recently, is that plant vesicles perform the same function as a type of animal cell vesicle, called an exosome, does. Their job is to take material from the interior of the cell, attach itself to the inner plasma membrane, create an opening, and then release the material into the apoplast, which includes the cell wall and the space between cells. Fungal cells do the same thing, but we didn’t know plants did until very recently. 

In animal cells, there are specialized vesicles that check the load being carried by other vesicles, to see if the contents should be destroyed or moved to the apoplast. Plant cells do not have those specialized gatekeepers, so there is still plenty to learn.

Now, this may not sound like a Big Deal, but this is how cells communicate with each other, triggering plant growth and defensive measures. In fact, exosomes are directly related to the production of defensive proteins and RNAs used to fight disease. Exosomes are also used to move those defensive proteins from nearby healthy cells to a cell under attack by a pathogen, to create protective barriers against disease, and they can even enter invading cells to inhibit their growth. [If you are interested in this sort of thing, it is called host-induced gene silencing.] On the down side, exosomes also play important roles in malignancy.

In the not-too-distant future, we may be seeing artificially generated plant exosomes crafted to boost our plants’ ability to fight disease. Similar studies are being conducted to see if plant exosomes can be used in human medicine, such as exosomes found to reduce alcohol-induce liver damage in mice, or how vesicles of the ginger plant may be able to reduce inflammation in the human digestive system. For now, I will stick with ginger tea, but maybe exosomes were the reason it has been helping all along…