# Why are red plants red?



## frozenoak (Jul 30, 2005)

I was thinking today...

If it is advantageous for a plant that uses chlorophyll to convert food to energy then it would seem to me that a plant would want as much as possible. Then I got to wondering if this might be a selected trait developed by horticulturists.

Does anybody know if natural selection or "intelligent" selection brought about the red in the plants we so cherish in our tanks?


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## gnatster (Mar 6, 2004)

See http://www.aquaticplantcentral.com/forumapc/showthread.php?t=435 for some information.


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## New 2 Fish (Dec 31, 2004)

I vaguely remember something from plant biology about different colored chlorophylls....
Anyone else remember that?


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## Phil Edwards (Jan 22, 2004)

Red pigments show up due to lack of Nitrogen and Phosphorus and are also plants' defense against damage from excess/excessive energy input. It's 11:00pm here and I'm about to go to bed. I'll have a more detailed answer for you tomorrow.


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## HeyPK (Jan 23, 2004)

Some tropical plants have red new growth that greens up later as it gets older. This either advertises that the new growth has bad tasting stuff or toxins and shouldn't be eaten, or it may just discourage herbivores because it doesn't look green and therefore probably isn't their food. 

I've always wondered about the brownish colors that many crypts develop when submersed. Why do they do it so readily when submersed, but not emersed? The browns may make the plants less visible to wandering herbivores. Are there herbivores that wander up and down the crypt streams in Sri Lanka? I have no idea. 

Plants have, in addition to chlorophylls A and B, yellowish xanthophylls and carotenoid pigments that also absorb some light wavelengths that chlorophyll is not so efficient at absorbing and they pass the energy from this absorbed light on to the chlorophylls by re-emitting the light energy at longer wavelengths that chlorophyll is more efficient at absorbing.


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## plantbrain (Jan 23, 2004)

Red coloration occurs more in some plants but the red plants still have chl.
Generally most red plants are in darker forest and rather than wasting precious Nitrogen for more Chl, they use the anthocyanins which are hydrocarbons(no nitrogen) that can help grab light at low levels and funnel it into the fewer chl molecules.

Intelligent selection? You mean artifical selection............we do that with crops, critters, etc.

Fast developing growth also has redder tips since the Chl takes longer and is more valuable to the plant to develop in new tissue, whereas the red pigments are cheap and easy to make.

UV protection is abother idea, but.........there are very few red desert plants and most tend to come from darker places with less light, the FW aquatic environment is fairly low light in most cases.

Low NO3 will cause more red color but so will high PO4 + moderate NO3 levels.

Regards, 
Tom Barr


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## Phil Edwards (Jan 22, 2004)

In areas or periods of high illumination plants will realign their chloroplasts into columns to allow light to pass through the plant more easily in order to avoid damage from excessive light energy. When this happens the red pigments that are ordinarily masked by Chlorophyll are unmasked and are more visible. 

Also related to light is the conversion of antheraxanthin into zeaxanthin as another defensive mechanism. As strong light hits the plant the pH within the thylakoid membrane (the Lumen, for you Tom) inside the chloroplast decreases. This tells the plant that photosynthesis is increasing and causes biochemical reactions that convert the antheraxanthin into zeaxanthin. Zeaxanthin is more able to absorb and dissipate the excess light energy away from the sensitive photosynthetic structures to avoid damage. 

What Paul and Tom said are applicable too, dependant on the situation.


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## frozenoak (Jul 30, 2005)

I guess I meant artificial selection Tom. If I went scuba diving in a fresh water lake (or pond) what are the odds I would run into a reddish tinted plant. 

Thanks for all the insights


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## plantbrain (Jan 23, 2004)

Quite high depending on where you lived.

We have red foxitail out here. 
Red Ludwigia in FL, Several red plants back east.

Red plants need basically the same things green one's need to grow.
Past literature and advice suggested otherwise.

Number of myth producing companies still sell "red plant" nutrients, say things that help plants "become red", namely iron rich ferts.

Regards, 
Tom Barr


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## ranmasatome (Aug 5, 2005)

so if they both need the same things to grow why is one different in colour than the other? okay..i guess..yes..they both need the same things to grow but in different amounts, the colour varies?


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## plantbrain (Jan 23, 2004)

The basic building blocks are the same, eg the hydrocarbons, this can be made into starch, sucrose, beta carotene, anthocyanins etc. Whatever the plant's genes tell it to make.

Chl and enzymes need lots of Nitrogen on the other hand.
There's still no Fe in this.

Fe is used mainly in PS 1 and enzymes, something all plants use.

Regards, 
Tom Barr


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