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My question is if a human were to have plant DNA, such as that from a flower, injected into their bloodstream would this have a negative or positive effect on their health? Or would it not affect them at all?

In this world, they have access to a larger amount of DNA.

By negative I mean would this kill them? Or would it possibly dwindle their immune system in any way?

By positive I mean would it strengthen their immune system. Give them some sort of minerals?

Or would doing this have no effect on the person in question at all? They would just have plant DNA in them.

I hope this question isn't too vague. I don't need a big in-depth answer just someone familiar with human immune systems and stuff like that and how they work just to know if it would be a negative or positive reaction or none at all.

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    $\begingroup$ You mean, injected in the bloodstream? It's a foreign substance as any other. Chances are that the kidneys will filter it out and it will be excreted. (DNA is not a protein, so the immune system won't get involved, most likely.) DNA as such seems to be not particularly toxic (see here for one of the few examples of tests); but then, nobody got to try with large amounts of DNA -- DNA is not usually available in bulk, not because it would be impossible but because nobody thought of any possible use. $\endgroup$
    – AlexP
    Aug 2 '20 at 19:12
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    $\begingroup$ In terms of mechanical properties, it depends on a few factors. DNA extraction techniques have a tendency to produce stringy jelly-like masses, would cause blockage in blood vessels, potentially pulmonary emboli - harm the patient's lung function when injected into a vein, but I'm sure you can find a way of handwaving that for a story if necessary. $\endgroup$ Aug 2 '20 at 19:36
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    $\begingroup$ I'm going to let someone with more biology than I have officially answer - but I could easily believe that not a thing would happen. The foreign DNA, which isn't doing anything other than float around int he blood stream (unlike a virus) would either (a) be broken apart and used like any other organic stuff, (b) be filtered by the kidneys and casually evicted in, perhaps, curiously lime-colored urine, or (c) would invoke the human immune system until (b) happened. $\endgroup$ Aug 2 '20 at 19:37
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    $\begingroup$ Please keep in mind that if you inject enough of anything into the bloodstream, it will eventually kill the host by displacing too much necessary blood. I'm jumping to the conclusion that such an amount is not being injected. $\endgroup$ Aug 2 '20 at 19:38
  • $\begingroup$ A more interesting question is what would happen if humans had chloroplasts inserted into their skin stem cells. $\endgroup$
    – John O
    Aug 2 '20 at 21:31
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It would have little to no effect if it was just "injected", since at that point it would just be harmless nucleotides. It would be captured and digested by lymphocytes.

It is possible that it might trigger an allergic reaction (but unlikely, since DNA is, well, DNA. Humans have it too).

To have an effect, the DNA would need to be injected inside the cells, or be bound to something that got inside the cells (in other words, a viral capsid) and then code for something that allows it to replicate. Being plant-based it couldn't reasonably infect the nucleus, so it would need to replicate in the cytoplasm of the cell. This isn't at all impossible (poxviridae do exactly that), but it does mean that the DNA must have specialized protein encoding sections for that purpose, and those sections would be useless in plants. In short, we're going farther and farther from ordinary "plant DNA".

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    $\begingroup$ Right, once you have DNA inside a delivery mechanism and it interacts with a human cell that actually does something, it is basically an engineered virus at that point and not some "Plant DNA". If a plant happen to have DNA that does all this magically, then that's just weird and you should call it something else, like a plant based parasite or toxin. $\endgroup$
    – Nelson
    Aug 4 '20 at 8:22
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DNA is a very stable compound. Unlike proteins, which get involved in all sorts of interesting reactions. DNA just sits there. It doesn't start replicating itself or synthesing proteins or doing any of the interesting stuff unless you supply it with a whole cell's worth of machinery.

When DNA was first discovered (and before Rosalind Crick and Watson figured out the structure), many doubted that it could be the gene; it was just too boring; it must be some kind of structural chemical in the chromosomes.

In fact, it is this very stability that makes DNA good as gene. You don't want your genes to be reacting with stuff and changing. You want your genes to sit quitely in the cell until the time comes for replication, and then only do replicate under careful control.

So you inject DNA into the blood, and your body will break it down. There are DNase catalysts in the body to deal with DNA that escapes for cellular damage such as may be caused by viruses or trauma. Too much DNA in the body's intracellular tissue is sticky and can cause problems, so the body is quite good at cleaning it up. (see cystic fibrosis, as an example of what can happen if this goes wrong)

There are no extra nutrients in the DNA, the chemical composition of plant and animal DNA are the same, it is just the order of the bases that differs.

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DNA viruses exists and our immune system responds to them. I don't think it would be any different if it is a plant DNA. Thus, in the end, it will have minimal effect on the host. The only effect I can think of is immune system response, fever, increased white blood cells, etc...

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    $\begingroup$ I'm not totally sure, but doesn't immune system react to virus's external structures rather than its RNA/DNA, which are packed inside those? I doubt it would react to pure DNA as it's not something commonly found in nature at all. P.S.: I was thinking of red blood cells, but those loss DNA before being released into blood stream and having a chance to break apart. $\endgroup$ Aug 3 '20 at 12:41
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I will suppose you mean gene injection through genetic therapy, possibly CRISPR-Cas, not merely dropping naked DNA on the blood stream.

Well, we already have plant genes.

Plants and animals have a common ancestor. They branched out in the tree of life about 850 million years ago, give or take. Probably on a Tuesday.

In evolutionary science, genes shared by different species may be orthologous:

Homologous sequences are orthologous if they are inferred to be descended from the same ancestral sequence separated by a speciation event: when a species diverges into two separate species, the copies of a single gene in the two resulting species are said to be orthologous. Orthologs, or orthologous genes, are genes in different species that originated by vertical descent from a single gene of the last common ancestor.

And here is an article by Dr. Natasha Glover, whose PhD is in plant genomics and biotechnology:

What genes do I have in common with a plant?

In short: we humans share 12,792 orthologous pairs of genes with the thale cress.

Our current estimate for the number of human genes gives us an amount of 46,831. So if you inject a thale cress gene in a human at random, there is approximately a chance of one in four that you will be just duplicating a gene. Depending on which one the person may get sick or may even become more resistant to cancer (if the thale cress has the p53 gene and you happen to copy that). Most likely, though, nothing will happen.

If you do happen to give that person a plant exclusive gene, though... Same results. You won't get a person able to do photosynthesis, because on top of that depending on a very complex set of genetic expressions, we don't have chloroplasts. You might get genes for resistance against the TMV virus, which is anticlimactic because it cannot infect humans anyway. But you may also create a human that is able to generate their own linoleic and α-linolenic acids, two kinds of unsaturated fatty acids, which would have zero impact on their general quality of life too.

Stan Lee said in his autobiography that if you are aiming to write a story set in a fantastic world with mutant superheroes, you should tone the science down. In this kind of fiction, the more you science things, the more boring things get.

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    $\begingroup$ You're two days off - it was a Thursday. $\endgroup$
    – Jedediah
    Aug 3 '20 at 16:54
  • $\begingroup$ @Renan Oops, never mind :D $\endgroup$
    – Narusan
    Aug 3 '20 at 19:53
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Semi-tangential response.

You explicitly ask about DNA. You could, instead ask about RNA. In which case, it is reported that plant RNA ingested in food can migrate into tissues and alter gene expression. No injection needed. (The picture for microRNA dietary uptake has become more complicated since the cited report, but has not been refuted.)

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  • $\begingroup$ If you were somehow making an extract of DNA from plants, it would likely contain a lot of RNA as well. They are very similar and would be difficult to separate. If you were making bulk DNA via something like PCR (why?) then it would be pretty much free of RNA. $\endgroup$
    – DWKraus
    Aug 3 '20 at 16:53
  • $\begingroup$ @DWKraus : DNA and RNA can be separated or one can specifically destroy the DNA in a sample (example product). $\endgroup$ Aug 3 '20 at 16:59
  • $\begingroup$ I was kind of making some assumptions based on the question, about what Ella was looking for, and trying to point out that your "tangential" response was likely relevant to what she was asking, since she said DNA and you said RNA. It's a bit of a quirky question, so I'm making guesses about her intent. $\endgroup$
    – DWKraus
    Aug 3 '20 at 17:03
  • $\begingroup$ Since I myself have quite limited knowledge about this sort of thing (hence why I am here) different opinions and mentioning different things such as RNA are very helpful to me. So thank you all :) $\endgroup$
    – Ella KZ
    Aug 3 '20 at 18:16
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Most likely boring case: it gradually gets eliminated through the same processes that normally take care of the circulating free DNA released by ordinary means

Somewhat unlikely bad case: it triggers some immune reaction if the recipient is unlucky enough. Since the foreign substance is in the bloodstream it's likely not going to be fun. Although this might be very unlikely with the DNA alone

Ridiculously unlikely case: that DNA somehow ends up getting into some business other than floating around doing nothing

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