carrots are orange because they are rich in carotene.carotene is a photopigment found in light harvesting complexes, alongside with cholorophylls, in photosynthetic leaves. it is believed that carotenes are present for protection against photobleaching, i.e. damage of chlorophyll due to overly strong sunlight, as they absorb the excess energy and lose them as heat.
but carrots are roots; they are buried in the soil.
so why do carrots have so much carotene o_O?
because they are edible and therefore must prove themselves to be nutritionally beneficial?
i am open to suggestions =)
3 comments:
Seriously... carrots, mei sheng? CARROTS???
here's something related. It doesn't quite answer the question definitely, but maybe it'll help.
from http://www.bio.net/hypermail/plantbio/1997-May/014584.html
Paul J. Strieleman wrote:
>
> I have a plant related question I can't find a good answer too. If the
> function of beta carotene is an accessory pigment for photosynthesis,
> why is it in such high concentration in carrots (a root) or squash (a
> fruit)? I assume it has some other function in the plant but can't find
> an answer. If you have time to ponder this I would appreciate it.
>
> Thanks
>
> Paul
Carotenoid pigments are synthesized in chloroplasts and do serve as
accessory pigments in photosynthesis. Perhaps more importantly, they
serve as protective pigments preventing chlorophyll from being
photooxidized. When chloroplasts degenerate during senescence, the
chlorophyll is degraded, leaving the carotenoids behind as the major
pigments in the plastid. This is why leaves turn yellow or red in Fall
before they drop. There is no function to this, it is simply a
consequence of normal senescence.
The carotinoids that accumulate in flower petals of many species
accumulate in chromoplasts, which are plastids that either derive from
pre-existing chloroplasts, or from pro-plastids that produce
chromoplasts directly. These evolved to function as attractants for
insect pollinators that can see the reflected ultra-violet light. The
same is true for the carotinoids in fruits like squash and tomato that
have evolved to attract herbivors (fruigivors?) that aid in seed
dispersal.
Why carotenoids, especially beta-carotene, accumulates in storage roots
like carrot is a very good, but unfortunately, unanswerable question.
Probably these roots are capable of producing normal chloroplasts, but
lack chlorophyll due to the lack of light and so produce chromoplasts
instead. Normally roots produce leucoplasts, which are plastids that
develop from the same pro-plastids in the dark that produce chloroplasts
in leaves in the light. Leucoplasts do not contain either chlorophyll
or carotenoids, but accumulate large quantities of starch. Unlike
chlorophyll in angiosperms, the synthesis of carotenoids does not have a
direct requirement for light. However, their synthesis is generally
stimulated by light, which may be why roots do not ordinarily contain
chromoplasts and make leucoplasts instead.
Hope this helps and if I said anything that is not accurate, I would
appreciate hearing about it before I teach it again in my Light and
Plant Development course.
Gerry Deitzer
Associate Professor of Horticulture
Department of Natural Resource Science and Landscape Architecture
University of Maryland
College Park, MD 20742-4452
another answer, from http://www.bio.net/bionet/mm/plantbio/1997-May/014496.html
Hi Paul. The thing is that wild carrots have very little beta
carotene in them. Many are white and I believe that one or two are
purple?? But, NONE of the wild carrots are orange in color. There was a
discussion about this about a month ago. May people believe that the
orange color and the Beta carotene in carrots are something that humans
bred. What I mean is that many believe that humans bred carrots to have
lots of beta carotene and to give it the orange color because I guess
that color is appealing!
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