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Re: Red plants and all
Philippe Lemaire asked:
"Why are plants green?"
They are green because they contain pigmented (colored) molecules called
chlorophyll. There are several types but they all have the "magic" property
of being able to take energy from light (sunlight or your fluorescent tubes)
and, via a series of steps, convert it into chemical energy which is stored
in starches and sugars. The main types of chlorophyll in higher plants are
chlorophyll a and chlorophyll b and there is a 3:1 ratio of a to b in higher
plants. Chlorophyll molecules absorb light primarily in two narrow bands,
one in the visible blue and the other in the visible red-violet sections of
the spectrum. Light energy in other areas (primarily the yellow and green
sections of the visible spectrum) is reflected and is what we see when we
look at a leaf containing chlorophyll (we see the color green). This doesn't
mean that colors of light other than blue or red-violet are useless to
plants, just that they use the blue and red-violet light which falls on them
MUCH more efficiently (like, with over 90% efficiency for blue light and
only slighty less for red-violet light). Yellow and green light however,
doesn't do much to excite a chlorophyll molecule.
"How do they produce photosynthesis while not being green (no chlorophyll)?"
Well, if they aren't "green" due to a LACK of chlorophyll, they don't do
much, other than wither away and die. The formation of chlorophyll requires
the full compliment of mineral nutrients be present and accounted for,
because while not all mineral nutrients are present IN chlorophyll, most are
needed in some part of the process thru which plant cells MAKE chlorophyll
(or carry out other life processes).
Some plants that lack chlorophyll live as parasites on other plants, which
DO have chlorophyll. The bottom line is - no chlorophyll, no growth (do not
pass GO!, do not collect $200.00, and don't even dream about taking a walk
along the Boardwalk...)
If you are thinking that plants which are red, yellow, or display foliage of
some color other than plain old "green" don't contain chlorophyll, you are
mistaken. There are a number of other pigments which act as accessories in
photosynthesis. Some of these, such as Carotenoids and Xanthophylls are
thought to have a variety of functions. They don't replace the chlorophyll,
but they can help it do its job more efficiently. These other pigments
absorb light in different areas of the light spectrum than chlorophyll does,
thus widening the range over which plants can extract energy from light.
They don't directly do the same things that chlorophyll can do, but they can
funnel the energy they extract from light to chlorophyll molecules, helping
them do their's. Usually, these accessory pigments are yellow, orange or red
and this color gets masked by the green of the chlorophyll, but in some
cases it can "shine thru" and you can see the leaves in their multicolored
One very important function of some of these auxiliary pigments is to act as
a form of protection for chlorophyll molecules against the free radicals
which can be formed within the cells under intense light. Sort of like
molecular sun shades. In cases where this happens, the red or violet color
of the auxilliary pigment can visually overpower the green color of the
chlorophyll and the plant will appear red or purple (Ever see an apple that
had one side red while the other side was green? The red side was in
sunshine, the green side was in shade. The apple produced more red pigment
in the sunlit skin to protect itself from the damaging effects of too much
light. At least, that's one theory....).
But please, don't ask me why some onions are red. I haven't a clue what the
plant is trying to do there...
"Are they better as young (and reddish) then give up turning green?"
What could be happening here (pigmented young shoots and leaves, which turn
green as they mature) is that the plant might be protecting tender, young
shoots from the potentially damaging effects of intense light. As they
mature, they are better able to cope and so the percentage of green
chlorophyll in the maturing leaves and shoots increases, overpowering the
color imparted by the auxiliary pigments.
A lot of the plants we grow in aquariums have colored leaves because they
were BRED that way or the color is due to a (non-harmful) virus. Many
varieties of Echinodorus are greenhouse products which have been carefully
selected over many generations - the more variegated and colorful the
leaves, the more selective breeding was done to encourage the trait. What
might have started out as a "sport" or a genetic mutation gets fixed into
the genetic makeup of the plant. There is also a plant virus called
"Rosanervis" which can infect some species of plants and cause the leaves to
lose the ability to produce chlorophyll in certain areas. This is seen most
often in Hygrophila.
If you want to maximize the "colors" that your aquarium plants produce, make
sure that they have optimum conditions in which to grow - give them
sufficient nutrients, including CO2 and light that is as close to full
sunlight in spectrum as modern lighting technology can provide. You are
lighting an aquarium for two reasons - to encourage photosynthesis in the
plants and to see the plants and fish with your eyes. The wavelengths our
eyes are most sensitive to are not the same ones most useful for
photosynthesis, but you can kill two birds with one stone (light) by using
full spectrum bulbs that will provide all of the colors of the visible
spectrum in a manner similar to sunlight. Forget the colored filters, reef
tubes, or those designed to stress particular portions of the specturm over
others. Mother Nature has been at this for billions of years - who are we to
think that we can do better?