13
$\begingroup$

I have fruit trees that grow "golden apples".

These apples:

  • have skin that superficially resembles gold in its specific color and metallic luster.
  • are edible enough that animals willingly eat them.
  • can be bitten and chewed.

The skin isn't made of actual gold. Its appearance proves highly attractive to animals, which proceed to eat the apples and disperse their seeds. Eventually, humans discover the golden apples and become enamored with them, further guaranteeing the trees' propagation.

Is there a possible natural mechanism that could explain the skin of these golden apples?

Improve this question
$\endgroup$
4
  • 2
    $\begingroup$ It might be fun to use actual gold if it is in abundance in the ground. It could be just as inert as in humans, but still get absorbed from the ground and extruded by the leaves/flowers/fruits, leaving behind a thin gold coating on the outsides of those. In a hot place it might even be helpful by blocking some of the sunlight, or providing cooling surfaces in some organic version of radiators. $\endgroup$ Commented Jan 21 at 13:41
  • $\begingroup$ I'm told persimmons (especially these ones) can look pretty much like they are made from gold in sunny weather. The yellow variety, some are more orange. $\endgroup$ Commented Jan 21 at 16:59
  • $\begingroup$ There's a breed of grapes called "scuppernongs" that often appear to have a golden or bronze color and luster. See the Wikipedia article at en.wikipedia.org/wiki/Scuppernong (though, upon review, perhaps images from a web search might be more illustrative). $\endgroup$ Commented Jan 21 at 20:49
  • $\begingroup$ Golden Delicious. $\endgroup$ Commented Jan 21 at 22:45

4 Answers 4

Reset to default
22
$\begingroup$

I suppose you wish your fruit to look golden once ripe and not just while they're still developing and, lucky you, we do have yellow apples on earth that look pretty golden in color! This is just one of many varieties.

Now, they do not have the metallic luster you're aiming for and, to that, I raise you marble berries, Pollia condensata. Their skins have the same type of structural composition that some butterflies and beetles have, providing their metallic sheen.

The only problem is that this specific structure reflects blue light rather than yellow, and I do not have enough physics knowledge to tell you wether the same type of structure could reflect yellow. (apparently they're called spiral structures and can, indeed, reflect yellow according to user @Themoonisacheese!)

What I do know, however, is that there are golden beetles! And for that I raise you golden tortoise beetles, Charidotella sexpunctata. They use a different mechanism to get their color, but hey, if fruits can use one beetle's mechanism for their iridescent blue, I can't see any good reason why they couldn't use another's to look golden!

Improve this answer
$\endgroup$
8
  • 5
    $\begingroup$ Well done! I could see a genetic engineer of the future using this path to make something like this. $\endgroup$ Commented Jan 21 at 19:46
  • $\begingroup$ spiral structures are very much capable of constructively interfering in the yellow range, and there's nothing nominally stopping it from developping in plants. The only issue i see left is "what kind of evolutionary pressure made it yellow that way instead of the much cheaper other versions of yellow" but nature is weird sometimes. $\endgroup$ Commented Jan 22 at 16:04
  • $\begingroup$ @Themoonisacheese, I suppose it could be due to the fruit's flesh not being as attractive to animals as other fruit. The marble berries I mentioned are, roughly, the same color as blueberries, just with an added metallic sheen, but they aren't particularly tasty, so the flashy skin helps it attract animals that would otherwise ignore it in favor of tastier fruit. So, I suppose if those golden apples taste kinda bland in comparison to other fruit that exists in the area, it could make sense to invest in a little glam. $\endgroup$ Commented Jan 22 at 18:19
  • $\begingroup$ What governs the color of the marble berries is not the size of the berry, it is a structure parameter of the special layer of cells in the peel which make the reflected ambient light interfere constructively around a given wavelength. There is no theoretical obstruction to the plant's DNA favoring a wavelength 30% longer (copper red) than IRL (peacock blue). en.wikipedia.org/wiki/Structural_coloration#Fixed_structures $\endgroup$ Commented Jan 23 at 12:50
  • $\begingroup$ @FrançoisJurain, I'm not sure what in my text made you understand me say that it was the size of the berries what made them blue. I didn't mention size once. In fact I very clearly stated it was the structural composition of their skin. Also, user Themoonisacheese had already pointed out that the yellow color would indeed be possible to obtain through this same structure, which I too added into my text. $\endgroup$ Commented Jan 23 at 15:23
6
$\begingroup$

Frame challenge: I don't see many problems to use a literal gold skin

The skin of fruits is meant as a protection layer against bacteria and small parasites to keep the fruit and seeds healthy.
As gold is an unreactive material it definitely suits for a protective skin.
For animals (and humans) which are big and strong enough to break/bite through the gold skin, there would be no harm to eat the gold skin when it is thin enough. Some real-life noble restaurants even decorate their food with edible gold foil.

Living organisms which are able to transport and use metals is nothing too uncommon. For example we have iron in our blood to carry the oxygen.
For me a tree which is able to use and transport gold doesn't sound too unrealistically (though I am not sure if this is possible with real gold).

The drawbacks of this idea is that the tree has to stand somewhere where it has access to gold:

  • At first, this implicitly reduces the attractiveness of the golden apples for humans when it is fairly easy to access the gold source directly.
  • As a second point, it limits the environment where the tree is able to grow and it makes it difficult and expensive to cultivate this type of apple tree.

The benefits of this idea are:

  • The apples look perfectly golden as they are covered by literal gold.
  • Rule of Cool: Isn't a literal golden apple cooler than an apple which just looks golden?
Improve this answer
$\endgroup$
8
  • 7
    $\begingroup$ The problem I see with this is that gold is unreactive, making it biologically difficult to work with and generally unavailable for uptake from an environment. Not a hard blocker, just an obstacle that isn't adequate to stop the Rule of Cool. $\endgroup$ Commented Jan 21 at 19:49
  • 2
    $\begingroup$ +1 for ambition, but the biological justification “Living organisms which are able to transport and use metals is nothing too uncommon” is very tenuous — using compounds of metals is ubiquitous, but I don’t know anything that procudes metal in pure elemental form. Many pop-sci descriptions that suggest that (e.g. wasp with zinc-tipped ovipositor) turn out on closer inspection to be metal-enriched biological materials. Still cool, but not what’s needed here. $\endgroup$ Commented Jan 21 at 22:21
  • 1
    $\begingroup$ @PeterLeFanuLumsdaine The closest I recall are the deep sea molluscs that have a deposit of iron sulphides (e.g. pyrite) on their shell, so basically a normal shell with a coating of iron sulphide. There is also a fungus that is thought to trigger gold deposition via reaction between gold complexes and reduced carbon species in situ. nature.com/articles/s41467-019-10006-5 $\endgroup$ Commented Jan 22 at 1:22
  • 1
    $\begingroup$ It does not even require all that much gold. For a very thin layer of one or a few molecules thickness, the amount of actual gold needed is very small. $\endgroup$ Commented Jan 22 at 9:20
  • 1
    $\begingroup$ @vsz I can vouch for that. It was estimated that even 100 grams of gold could be hammered out to cover the entire surface of a large room and look just as impressive as seen in palaces. $\endgroup$ Commented Jan 26 at 9:12
5
$\begingroup$

Tomato is called, in Italian, pomodoro, literally "golden apple", because when they are still not ripe they have a golden hue (see here). Sometimes the golden hue is visible also on the leaves and stems.

The only difference with your fictional fruit is that they are not edible, but for the rest they pretty much fit the bill.

You can use the same mechanism.

IRL there are also tomato varieties which are golden yellow when ripe:

enter image description here

Improve this answer
$\endgroup$
2
  • 2
    $\begingroup$ I don't know about in general, but here in Romania fully yellow or orange tomatoes are not uncommon. $\endgroup$ Commented Jan 21 at 14:03
  • $\begingroup$ Yellow tomatoes (and for that matter peppers, plums, Sharon fruit, and no doubt others that don't spring immediately to my mind) do have a pretty yellow colour, but there's no way you could mistake them for actual gold. You are only calling it "golden" metaphorically, not literally, so you've got a bit of a category error there. (See also "Fields of gold", "Sister golden hair".) $\endgroup$ Commented Jan 23 at 9:49
4
$\begingroup$

There are viruses called Iridoviruses that, when present in sufficient concentrations, cause a metallic iridescent sheen to the infected organism. In real life, these are only found in fish and insects, but there is no reason that there couldn't be a plant virus with similar characteristics. The sheen is actually caused by thin film interference, much like an oil layer on water. If you adjust the interference by particle size you should be able to get a metallic gold appearance to the iridescence.

My model would be that the virus coincidentally aids in dispersal of the seeds. In the plant, it only shows up in the fruit when they are ripe because the replication kinetics are such that the time it takes for the fruit to ripen is also the length of time it takes to reach a high enough concentration to produce the iridescence. The sheen is visually eye-catching, which means that it attracts more animals than a non-infected plant and the animals are more likely to eat the fruit as they are obvious and ripe.

In the animal maybe the virus has a laxative effect, which causes them to defecate more frequently, so the seeds are shed with a nice load of fertilizer to help them grow.

Improve this answer
$\endgroup$

You must log in to answer this question.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.