Why can we make grafts from one plant to another slightly different plant and these are not rejected, but the human does reject grafts from a different human?

Submitted by Juan_D_2314 t3_11qw5xx in askscience

I was watching a documentary about the cultivation of vines in Europe for the manufacture of wine. In that documentary they mention that there was an insect that attacked European vines because the trees had thinner bark. However, the plague did not attack American vines because they had the thickest bark.

From this discovery, they began to cultivate American vines and they put grafts of European vines on them, so they would have a thick skin and they would give European grapes (since the American grapes from this vineyard were not very pleasant to the taste).

From here my question arises, do plants have defense mechanisms against other plants that may try to take advantage of their nutrients, cells and structures? Or can they detect when a plant is dominating gene expression to make the bark thicker? Something like a function similar to what the Major Histocompatibility Complex would do in humans, which detects foreign cells and those not typical of our body, rejecting these grafts.

(sorry in advance for grammar, english is not my first language)

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Revenge_of_the_User t1_jc5u19t wrote

Youre comparing apples to oranges.

Animals and plants have completely different systems evolved for dealing with things like infection and pests or parasites. Right down to cell structure.

Many plants have evolved such that a broken branch can heal to become its own entire plant (a genetic clone of the original) and a lot of that is down to cell structure and how relatively simple a plant is in operation.

Compared to how varied animals are; we span every environment to some degree, we consume a huge variety of food (which puts us at risk of as many different infections and parasites as you can imagine) we exist in various states of health for extended periods of time, and we have differing aspects of health (i.e. a tree needs sun, air, and water. We have dietary needs far more complex, we have mental health that can and does have physical implications) so for humans/animals, we evolved an immune system specifically for the purpose of handling many of these issues. And the issues are so varied, the immune system must make a distinction between the body its trying to protect and foreign material - else it cant do what needs to be done (the person dies due to a lack of effective immune system) or the opposite extreme where the immune system doesnt properly make the distinction between friend and foe; known as an autoimmune disease where it attacks tissues its supposed to protect. This is why it attacks another humans tissue. That tissue could carry disease or parasites, it isnt the tissue its programmed to protect. And the immune system has evolved successfully by attacking these things.

Animals and plants are very, very different.

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BubbaL0vesKale t1_jc6e30e wrote

Replying to Revenge_of_the_User (#2,226,392)

To add a note about plants: plants do have nutrient needs just like animals (ex: beets like extra boron). And different plants need different nutrients. And within the same species plants need different nutrients at different times of their lives (vegetative vs. fruiting). It's not just sun, water, air.

Plus plants have many symbiotic relationships with bacteria and fungi in their soils. The plants provide sugars to the soil and the bacteria and fungi help transport nutrients to the root zone. Different plants work with different fungi/bacteria so diversity of plants means diversity of soil biology.

None of this refutes your points, it's just more complex on the plant side than most people think.

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FallenFae t1_jc6r9fv wrote

Animal cells: permeable, squishy, weak yet adaptable Plant cells: rigid, self-contained, angular.

Grafting plants onto other plants is like building with legos, grafting animals to animals is like trying to stack jellyfish into the shape of the eiffel tower. It's a wonder we can even do it at all.

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FlattopMaker t1_jc9jrr9 wrote

Plants have defense mechanisms in some cases. But it's not always about defending against attack. Some plants deliberately give away their nutrients to other plants of other species to survive in an ecosystem.
Plants reject grafts when the unions don't heal. u/shiningPate provided a short explanation here about why plant grafts only work sometimes, but for different reasons than a human or animal allograft of tissues.

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