Relation to the plant's life cycle
Why plants change color The color in plants
Many people would agree that the most impressive season on the Blue Ridge Parkway is autumn. It is this season which allows the various plants to express their hidden color. These plants, which were once the soft deep greens of the forest, are now brilliant tones of red and yellow. Soon these hues will pass and the leaves will disappear. The plants will rest for a season and the bright green of spring will come again.
How is color related to a plant's
life cycle?
Most of the color appears in the leaves of the various plants, trees and shrubs. As you may know, the leaf is the food manufacturer of the plant. The food is manufactured by combining carbon dioxide with water. In the process, energy from the sun must be trapped by a pigment (colored) molecule called chlorophyll. Some other pigments help chlorophyll trap energy. Since food is a high element in the order of survival, you would expect that chlorophyll would be abundant in all plants. This is certainly true with few exceptions.
Color is most often the result of many internal changes. In the green plant, most of the chlorophyll must be removed before we can see what other colors are present. At the time of early fall, the cycle of a leaf begins and a layer is formed in the petiole (leaf stalk). This layer stops the supply of needed materials (phosphorus and magnesium) to the leaf. With this stoppage, the chlorophyll wears out and is not replaced as in earlier seasons. The other colors, yellows, reds, blues and violets are more long lasting than chlorophyll. They last out the chlorophyll and show through until the end.
The Indians had a theory that blood dripping from the Great Bear (Big Dipper), that was shot by the sky hunter, dotted the mountain side in the red maples and other red plants. And, as the meat was cooked, the fat that spattered out of the kettle landed on other trees to form yellows. We have discovered in previous statements that the change of color is based on chemical processes which take place in the leaves as the season changes from summer through fall to winter.
We should examine the basic pigments that cause fall color to see how they contribute to the season and just what they require to exist.
The GREEN color is caused by the abundance
of chlorophyll. Chlorophyll a and b are present in most of our seed-producing plants. The
difference in these two molecules is slight; therefore, we refer to them collectively as
chlorophyll. They can be found in roots, stems and leaves provided they are above ground
and exposed to light. Chlorophyll is not found in the internal tissues where light will
not penetrate such as the wood of the tree or the flesh of an apple; nor is it usually
found in such underground structures as roots and tubers. Although it appears to be absent
in yellow or red leaves, if these colors are removed the chlorophylls can be found.
The YELLOW color is produced by the presence
of yellow, orange and red pigments collectively known as carotenoids. There are two groups
of carotenoids, the carotenes and xanthophylls. The carotenes are much like vitamin A and
may be converted after eaten by animals. The coloration of carrots (providing the name),
pumpkins and green and yellow leaves is due to the presence of carotenes. Xanthophylls
(meaning 'yellow leaf') are found in many flowers such as dandelions and sunflowers. The
color of corn and even that found in egg yolk and butterfat is due to this group.
Carotenoids are important as a supply of Vitamin A, in attracting insects to pollinate
flowers, attracting birds to fruits for seed distribution and aiding chlorophyll in
trapping the sun's energy.
The RED, BLUE and VIOLET colors are caused
by the production of anthocyanins. These pigments are not contained as the previous two
pigments, but are randomly distributed in the fluid portion of the cells. The presence of
an acidic or basic alkaline environment in the cell fluid determines the color shown. If
the cell fluid is acidic then the color will be red. If the cell fluid is basic then the
color will be blue. Anthocyanins will dissolve in water so if red leaves are boiled the
water will take on a reddish color. This is most obvious when beets are boiled prior to
eating.
Another group of color producers are
flavones. They too are yellow and often tint the color of boiled water when green leaves
have been introduced. These are chemically like the anthocyanins and will dissolve in
water. One of this group is found in sumac, horse chestnut, tea and onions.
Tannins are responsible for the brown color which often color the waters of rivers and streams in the fall and also after the floods of spring. These too are dissolvable in water and may be seen in tea, chestnut bark and fruit as well as in any plants which have a brown color.
These are things in general which cause color. As you proceed along the Parkway enjoy the beauty of our fall color and think for a moment. The internal and external processes and the warm sunny days and cool nights without frost bring us this seasonal magic.
