The Fall Color

 Fall Color

P.K.Ghatak, MD

No 55.

Fall Colors.

Every year before the long winter sets in, Nature presents us with the most spectacular display of Fall Colors. Those who live along the mighty Rocke mountains, on the shores of the Great Lakes, Catskill and Blue Ridge mountains are fortunate to enjoy the treat each year. The leaf colors of the deciduous trees last only about 3 weeks and are often delayed or cut short by adverse weather, however, dazzling colors make people happy.

We take it as granted and do not think much about the chemistry or science of plant physiology at all.

Where the colors come from:

The Green is the color of chlorophyll which gives the leaves their green color. Chlorophyll is produced in the Chloplasts within the leaves and also present in the green stems and green branches. The chlorophyll is made up of 4 pyrrole rings, like human hemoglobin with an exception having metal magnesium in the center instead of iron as in the hemoglobin. And like hemoglobin, chlorophyll is broken down to its components by enzymes. Without going into details, and stated simply, with the approach of short days and cold weather the tree takes the sap out of leaves and transfers the nutrients to the branches and trunks. And the enzymes start to break down chlorophyll.

As the degradation of chlorophyll takes place the other colors that are already present in the leaves become visible.

What are the other colors:

Yellow, red and brown and various shades in between giving rise to a wide spectrum of colors.

One step in the color chemistry:

Carotenoids:

As the name points the carotenoids are a mixture of several pigments, chiefly among them are carotene, lutein, xanthophylls and violaxanthin.

Carotenoids give yellow, orange, red colors and various shades of these colors. Carotenoids are most abundant in vegetables like spinach, broccoli and parsley. That is why one sees stale broccoli turns yellow in a short time in the refrigerator.

The leaves of Aspin, Birch, Sugar Maple, Hickory, Ginkgo, Poplar, Sweet Cherry, Apple and Apricot contain high amounts of carotenoids but are not visible due to the dominant green color of chlorophyll. In the fall as green fades carotenoids take the stage.

Protective action of Carotenoids.

Carotenoids absorb UV light of the sun but a different wavelength from that of chlorophyll; it shields delicate chloroplasts from harmful effects of the UV light.

Anthocyanins.

Anthracenes are not initially produced by the leaves along with green and yellow pigments. It is made fresh in the fall. Anthocyanins display red and purple colors in a brilliant hue.

Anthracenes are polycystic hydrocarbons having 3 rings of benzene. It is mildly aromatic.

The leaves of the following trees have high amounts of Anthocyanin.

Maples. Sumac, Tupelo, Sweetgum, Red oak, Sourwood and Japanese Maple.

Ash and Oaks lack anthocyanin and leaves of these trees do not display red color.

Tannins and Flavonoids:

Tannins.

This gives the tree leaves a brown color in the fall, and it seems that the brown color does not fade even when all other colors are gone.

The leaves of the following trees contain a high amount of Tannins.

Black Oaks, Chestnut, Sumac, Mimosa and Hemlock.

Tannins are complex phenolic compounds and are polymers of phenolic acids, usually found in the wax and vacuoles. The compounds have garlic smell and plants use it for defense mechanisms.

Flavonoids. Flavonoids are catechins, a kind of condensed tannins. It is found in seeds. Skins, stems and wood of most plants.

Riboflavin.

Riboflavin is a yellow to yellow-orange color and glows under UV light. Human vitamin B2 is a riboflavin. Green vegetables, almonds and whole grains are sources of this vitamin.

__________________________________

Footnote:

We talk” plants and animals” then immediately switch to chemistry and biology of the animals.

Save and except for the Tube Worms of the deep seas and a few heat - loving rare bacteria of geysers,

all other living animals on the Earth depend entirely on the plant produced food and nutrition.

Like animals, the plants also have living cells, cell membrane, nucleus, nucleolus, mitochondria,

Golgi apparatus etc.etc. Plants collect basic ingredients for manufacturing sugar, proteins, hormones,

enzymes, antioxidants, toxins and alkaloids.  And like animals carry on cellular respiration and use

sugar to generate metabolic energy and exhale CO2.

Chlorophyll.

The molecular structure of chlorophyll and hemoglobin are the same. It contains Magnesium

instead of Iron which is attached to 4 nitrogen atoms at the center.

Porphyrin is a cyclic compound made of 4 Payroll rings. Each Payroll molecule has one N at the center,

4 payrolls come together to form a Porphyrin. Porphyrins are found in nature as various compounds.

however, the plants synthesize Porphyrins in the living cells from succinate derived from

the Citric Acid Cycle and the Amino Acid Glycerin.

Sugar

The main plant sugar is hexose sugar, C6 H12 O6. In addition to hexose plants also make Fructose,

Sucrose, Sorbitol, Pentose, Arabinose also a Pentose (pectin and hemicellulose), Starch and

Cellulose. The cellulose is a complex carbohydrate which is the main bulk of the trunk and branches

of a tree.

The conducting tissue that makes up the bulk of the tree trunk is cellulose reinforced by lignin.

Glutens provide cells with a firm stable outer structure.

Toc & Tic protein compounds specially mentioned here because they transport raw materials to

Chloroplasts.

Hormones:

Auxins. Promote cell elongation and growth.

Cytokines. Required for cell division.

Gibberellins. Seed germination and plant's stress response.

Enzymes: The most important enzyme for all species of this world is RuBisCo. (Ribulose-1,5-bisphosphate carboxylase/oxygenase)

Ribulose biphosphate Carboxylate / Oxygenase catalyzes CO2 from the air in the production

of sugar, the process in known as Photosynthesis

updated: February 2026
###########################################################################

http://www.ghataksays.blodspot.com