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Discussion Starter · #1 ·
Plants are typically green because they absorb red and blue wavelengths and reject green ones. So why are some plants red? I'm sure they didn't change their whole metabolic machinery and reject red wavelengths, right?

I know co2, high light and steady iron (along with strictures on no2) encourage redness, but I still don't get it. Does iron "dye" the leaves? It has to be something like that, right?

I searched around for an answer to this but found nothing.

I'm confident I won't understand the answer I receive but will try to sort it out.
 

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Most plants you see (the green ones) have a pigment called chlorophyll that they use to absorb light for photosynthesis. Chlorophyll reflects green light, which is why these plants appear to be green. However, some plants have pigments called carotenoids in addition to or instead of chlorophyll. These pigments usually reflect orange/red light, which is why these plants appear orange/red. I'm not sure as to the exact cause for the different pigments but I'm sure someone else on here will know.
 

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Discussion Starter · #3 ·
Most plants you see (the green ones) have a pigment called chlorophyll that they use to absorb light for photosynthesis. Chlorophyll reflects green light, which is why these plants appear to be green. However, some plants have pigments called carotenoids in addition to or instead of chlorophyll. These pigments usually reflect orange/red light, which is why these plants appear orange/red. I'm not sure as to the exact cause for the different pigments but I'm sure someone else on here will know.
That's a perfectly concise answer. The cause, as you mentioned, would be great to know. Evolution is a beautiful thing.

Thanks.
 

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The red (and sometimes other colored) pigments like anthocyanins and other pigments like phycobilins serve at least two purposes that are known:

1) It lets them harvest light for photosynthesis at different wavelengths than just the ones chlorophyll a and b can absorb. It lets them get a little more energy per day than they'd otherwise be able to absorb. (I think the boost amounts to 5-10 Watt - Days/Square Meter) The underlying basis for this devolves into quantum chemistry, which is probably a little too much information for your question.

2) Handling light generates a lot of high energy electrons, which often creates super reactive molecules (free radicals) as unwanted side products. Free radicals bounce around cells and start reactions that cause things in the cell to self destruct. Because they're such large targets, cell cycle controlling proteins and lipids, as well as DNA, are particularly susceptible to those sorts of reactions. Instead of the important macromolecule taking the hit, the pigment molecules are there to scavenge free radicals before they can do any damage.

Plants have regulatory systems in place that let them determine how much light they're getting over an accumulated period of time. Once they absorb enough light at a specific wavelength, the genes responsible for producing the scavenging systems (including the pigments) get expressed in proportion to the amount of light they're being exposed to. Photosynthetic bacteria do the same thing, including cyanobactyeria, purple non-sulfur, and purple sulfur bacteria.

That's why some low light aquarium plants like crypts get red or purple when you increase their light exposure- they've hit their threshold for exposure and are using it more or less like sunscreen. The color is red instead of yellow or purple or plaid because of the energy levels the pigment can deal with. (Quantum physics got started when people figured out that colors, energy levels, and molecular composition are all related)

When researchers talk about the health benefits of red wine or blueberries, it usually involves these sorts of molecules. They work just as well in animal cells as plant cells since the underlying physics and chemistry is the same no matter what sort of organism you're looking at.

As for Iron, I'm not sure what the relationship there is, aside from systems that need to ferry a lot of electrons around like photosynthetic reaction centers use a lot of Fe-S clusters, but those wouldn't be red. The only iron associated red pigments I'm aware of have some sort of heme cofactor, like leghemoglobin. Since those are used as symbiotic nitrogen fixation associated oxygen carriers, you'd find them in legume and conifer roots, but not their leaves or needles.

Hope that's complete without being too wordy.
 

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FLC, that's a great explanation.

I did once read a scientific paper, and if my understanding of it is correct, it stated that iron increases oxidative stress from light-generated free radicals. Excess iron + excess light = more "sunburn", and thus more "sunscreen" is generated to compensate. Which would certainly explain why heavy iron dosage is commonly associated with getting good reds from plants, despite iron not being a component of these alternate pigments.
 

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Very cool... Makes me wonder about the macro algae commonly called Dragon's Breath. It's a burgundy red with orange "leaf" tips.

Would red leaves mean a higher light requirement?

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It's not entirely clear that anthocyanins are effective in neutralizing free radicals produced through the metabolic processes in leaves simply because most are located in the vacuole and thus, are separated from metabolic reactive oxygen species.

What anthocyanins do as "sunscreens" is absorb blue-green and uv light to protect tissue from photoinhibition.

It's not quite clear if Iron induces the red. High-light is your best bet to get the red to show in plants known to display it. However, it's been suggested that this only accounts for the redness in the uppermost leaves of stemmed plants (those closest to the light). It may not account (likely it will not) for uniform redness.

For that, it has been suggested that "stressing" these plants helps induce the reds and purples throughout the stem. Anecdotally speaking, people have accomplished this by limiting NO3.
 

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Thanks, is what I was thinking.

I have orchids, many of those will do that suntan thing when receiving a bit too much light, especially on the newest growth.

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Epic post FLC
i'm also leary on the free radical concept, althought it does bear merrit

in summary
lots of light means plant wants to protect itself and will generate more pigments to reflect light away frm the chlorophyll. this also becomes a double edged sword. these plants cannot produce hgih quantities of these pigments without adequate Co2.
for instance ludiwigia sp.red, so its been called, will actually be a slight green color if set in full sun with no co2 added, but it clearly is red in a tank with lower lighting and no co2
yet when added to a super nuke lighting tank with good co2, it becomes a deep almost purplish red.
so there is a recipe to make a red plant, red..
reducing nitrogen reduces chlorophyll production which allows more pigments to show through. they are naturally there just hidden by chlorophyll. this is not a safe way to grow a plant and is likely to cause more problems than good
the easier and faster growing method is just a healthy growing plant with more light than it need to survive
 

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Discussion Starter · #11 ·
Thanks for the great explanation flc, et al. I always thought when a plant turns red it's because it's found its "happy place." But if I'm understanding this correctly, redness is actually a defensive response to a stressful environment?

So point two of flc's post is currently being debated/tested?
 

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Thanks for the great explanation flc, et al. I always thought when a plant turns red it's because it's found its "happy place." But if I'm understanding this correctly, redness is actually a defensive response to a stressful environment?

So point two of flc's post is currently being debated/tested?
you are understanding correctly!
Plants do respond defensively to more than neccessary light levels.
Some plants do not have said defense mechanism because they can accept and utilize more light than we can give.
 

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its a defensive response, but not to a stressful environment. it neutralizes the stress.
think of the red and yellow pigments as the plant's version of the animal pigment melanin. it blocks harmful radiation. since the radiation is blocked, no harm done.
putting me out in the sun causes me to brown (tan), once i have tanned, the radiation no longer harms me. sure, cancer is a possibility for me, but not for your plants.
 

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"Bronzing" occurs in terrestrial plants too, on which a lot more research has been conducted. In response to excess iron, and other photosensitizing agents.

Short, daily blasts of very intense light is reported to generate some awesome reds. Though it's a little easier said than done. I did try with a halogen worklight once, but stopped when I realized how fast the tank temperature was rising.

Another time I put a bag of Ludwigia Repens into a tanning bed. :) No result though. It could be that a single exposure isn't enough, or perhaps the bag didn't pass much UV.
 

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"Bronzing" occurs in terrestrial plants too, on which a lot more research has been conducted. In response to excess iron, and other photosensitizing agents.

Short, daily blasts of very intense light is reported to generate some awesome reds. Though it's a little easier said than done. I did try with a halogen worklight once, but stopped when I realized how fast the tank temperature was rising.

Another time I put a bag of Ludwigia Repens into a tanning bed. :) No result though. It could be that a single exposure isn't enough, or perhaps the bag didn't pass much UV.
Ludwigia repens will take a lot of abuse before turning red.
It can tan itself in about a day worth of lighting if its strong enough
 
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