Why can you graft onto a plant? You can graft onto a plant because they don’t have an immune system.
There are several ways of grafting plants, but the method I am thinking about is called cleft grafting. In cleft grafting, a cleft is cut into the trunk of a tree of the stalk of a plant. A branch or a part of another plant is cut off and the cut end of that cutting is inserted into the wedge cut in the first tree or plant. The opening is then covered with something called grafting wax which protects it while the graft takes. Within a short period of time, the cutting from the second plant has become part of the first plant, sharing cells and the same circulatory system.
Humans have been grafting plants for thousands of years. There is evidence that people were grafting plants in China in 2000 BC, and it is likely that they had been doing it for a long time before then. There is no written evidence before this and grafted plants obviously don’t remain, so there is no way of knowing exactly when it started. They could have got the idea when they saw plants that grafted naturally. If two trees are growing very close to each other and their branches are touching, the friction caused by the wind could rub the bark off both limbs. When that happens, the two limbs can join together and become one. This is natural grafting.
There are many reasons why we graft plants. You can make stronger plants by grafting a weaker one onto a stronger one. There are some trees that might not be able to survive in a certain soil, but if you graft them onto the trunk of a tree that can survive in that soil, they will grow and survive. You can do the same thing with pests or diseases. If you graft a plant that is vulnerable to a certain pest or diseases onto one that isn’t, the plant will grow. You can change the height of a plant. Apple trees are usually quite tall but shorter trees grow more fruit and the fruit is easier to harvest, so they graft the apple tree onto a dwarf tree, which makes it much shorter. You can do the opposite as well. By grafting you can make hybrid plants. If you graft one kind of fruit tree onto another, you can get a new kind of fruit. You can make trees produce fruit more quickly as well. New trees take several years to reach their fruit bearing stage, but if you graft a young tree onto an older one, it will produce fruit much sooner. It can prolong the life of a tree as well. If a tree is getting old, grafting it onto a younger one will give it a new lease of life.
So, how does grafting work on a biological level? It works because of the way plants heal themselves when they are injured. Plants have an interesting way of healing themselves. Their cells are very rigid to keep the structure of the plant, and they are always under pressure. When you cut off part of the plant, the pressure drops, and the surrounding cells stretch to fill the gaps. This motion triggers the nearby cells to start dividing until there are enough new cells to bring the pressure back to what it is supposed to be, which means they have sealed the gap. The cells on the outside of the plant are not the only ones that change. The cells that make up the vascular tissue, the vessels that move water, nutrients, and sap around the plant, also grow when the plant is cut. If you cut through the vascular tubes, the cells start to divide and push the tube out, almost searching for the part of the tube that was cut off. If they find the other part of the tube, they seal back together again. This is why grafting works. The first step is to remove the cutting from the plant to be grafted and cut the cleft into the second plant. The two plants have to be put together relatively quickly because when a plant is cut, it will start to heal itself and seal over the wound to avoid losing water and nutrients, or to be open to bacteria and pests. When you graft a plant, the two parts go together before they have sealed up their own wounds, but the healing process continues as normal. The only difference is that the cell walls of the two halves expand against each other and the cell division creates new cells that seal the two pieces together. Inside the plant, the vascular tubes grow as well, searching for the cut off part. The tubes from the original plant and the cutting plant meet and grow together. When this has happened, the plant is successfully grafted.
The main reason this can work in plants is because they don’t have an immune system. Plants are static and cannot run away from danger in the way that we can. They have evolved to be able to change their own chemistry in response to changing environments and dangers. That means, when a second plant is grafted on to them, they change their chemistry to accept it, passing genes to each other. If you did that to a human, our immune system would register the threat and reject it, as you see with organ transplants.
That being said, you cannot graft any plant to any other plant. If lants are too genetically different, the graft won’t take. You cannot graft plants in different families together. You can graft two types of apple tree, but you cannot graft an apple tree to a banana tree. The reason for this is not the genetics so much as the position of everything within the plant. If the vascular systems are not in the same place, they can grow all day long and they will never meet each other. And this is what I learned today.
Photo by Photo By: Kaboompics.com: https://www.pexels.com/photo/a-person-in-red-nail-polish-holding-plants-6640498/
Sources
https://www.colorado.edu/cumuseum/sites/default/files/attached-files/why_do_we_graft.pdf
https://en.wikipedia.org/wiki/Grafting
https://www.sciencedirect.com/science/article/pii/S1674205223004008