Changing Colors of Leaves

Nature is a great chemist. It is playing with chemical pigments to present vivid colors. Even a single leaf is a piece of art. There are many classes of pigments present inside it but their amount and times of breakdown and synthesis decides the resultant color.

The different colors are on display during autumn season. The leaves begin to look less and less green. They can take yellow, orange and red hues depending upon the ratios of the amounts of different pigments present in the leaves.

Most important pigment in the leaves is of course the chlorophyll. It is this pigment which imparts the green color to the leaf and helps in photosynthesis. It’s amount is dictated by the warmth and amount of sunlight the plant receives.

It’s presence is the indication that plant is alive and carrying out photosynthesis to convert carbondioxide and water into sugars and oxygen. Sugars contain energy from the sun which is harvested by tree or plant during photosynthesis.

What happens when it is not sunny. We see a kaleidoscope of different colors in leaves. There are yellow, orange and red hues. These colors are attributed to other pigments present inside the leaves. These were there throughout the life of the leaf but there colors were masked by the strong green color.

In the autumn, when sunlight is not available in plenty, the production of chlorophyll is halted. Chlorophyll present in the leaves begins to breakdown. At this time, color contribution from other pigments begin to show up.

Chlorophyll is a type of complex with Magnesium as the central metallic ion. There are 4 nitrogen atoms which are Lewis bases and thus trap the positively charged Magnesium ion. Chlorophyll is synthesized in the warm and sunny conditions by the plants.

It’s green color dominates the color in the leaves. During autumn, the sunlight is not fully available and hence the production of chlorophyll halts and since it is not required the already present chlorophyll in the leaves begins to breakdown and hence result is the decrease in green color of the leaves.

Carotenoids and flavonoids are the other pigments which are always present in the leaves but their color is masked by the green color of the chlorophyll.

When during autumn, the chlorophyll begins to breakdown, the color of these two classes of compounds begins to show up.

Xanthophylls which are oxygenated carotenoids are responsible for the yellow color of leaves. They do not require light for synthesis, so that xanthophylls are present in all young leaves as well as in etiolated leaves.

A class of carotenoids known as beta carotene is responsible for the orange color in leaves. It absorb light of green and blue wavelengths and reflects red and yellow wavelengths light thus causing the orange color in leaves during autumn.

Beta-carotene are also responsible for this color in carrots. They begin to degrade at the same time as chlorophyll but at a slower rate thus showing up the orange color gradually.

There is another class of compounds called anthocyanins which begins to get synthesized in the mature leaves due to the high amount of sugars in them. These are red in color. These are thought to prolong the falling of leaves.

Chemistry of leaf colors

Leaves of plants are the factory units for making the food in the form of sugar from carbon dioxide, water and light by a process called photosynthesis. The process is accomplished with the help of chlorophyll which belongs to a class of organic compounds called porphyrins.


We also have noticed that plants leaves change color especially when the amount of light available changes with the change of weather.

Chlorophyll exists in two forms namely Chlorophyll A and Chlorophyll B. It’s production in the plant is dependent upon the amount of sunlight available. It also decays at a continuous rate irrespective of the sunlight availability. When the sunlight reduces on the onset of winter, the production of chlorophyll is reduced.
Chlorophyll imparts the green color to the leaves. When new leaves sprout their colour is light green and becomes darker green with the passage of the time. But in winter why the color of the leaves become brown, yellowish? This means the leaves contain other pigments also. The resultant color is a mixture of ratios of the pigments present.
There are three main pigments which impart the different colors to the leaves. These are Chlorophyll which we have discussed above, Carotenoids, and Flavonoids.

Carotenoids belong to the class of organic molecules called carotenoids. Examples of carotenoids found in leaves include lycopene, which is red, and xanthophyll, which is yellow. Light is not needed in order for a plant to produce carotenoids, therefore these pigments are always present in a living plant. Also, carotenoids decompose very slowly as compared to chlorophyll. Carotenoids are present in many vegetables also like carrots from which they derive their name, papaya and other red or yellow coloured vegetables and fruits.
Examples of flavonoids include flavone and flavol, which are yellow, and the anthocyanins, which may be red, blue, or purple, depending on pH due to the transformation of the basic structure on receiving or releasing the proton depending on the soil fluids pH.

Anthocyanins, such as cyanidin, provide a natural sunscreen for plants. Because the molecular structure of an anthocyanin includes a sugar, production of this class of pigments is dependent on the availability of carbohydrates within a plant. Anthocyanin color changes with pH, so soil acidity affects leaf color. Anthocyanin production also requires light, so sunny days are needed for the brightest fall colors

When leaves appear green, it is because they contain an abundance of chlorophyll. Chlorophyll masks other pigment colors. Anthocyanins, in turn, mask carotenoids. As summer turns to autumn, decreasing light levels cause chlorophyll production to slow.

However, the decomposition rate of chlorophyll remains constant, so the green color will fade from the leaves. At the same time, anthocyanin production in leaves increases, in response to surging sugar concentrations. Leaves containing primarily anthocyanins will appear red. Leaves with good amounts of both anthocyanins and carotenoids will appear orange. Leaves with carotenoids but little or no anthocyanins will appear yellow. In the absence of these pigments, other plant chemicals also can affect leaf color. An example includes tannins, which are responsible for the brownish color of some oak leaves.

Incidentally, some of these pigments do not undergo decomposition and remain unaltered during the decomposition of other organic material to petroleum and coal precursors. These are called biomarkers and are used to delineate the source of petroleum and coal forming organic matter in terms of terrestrial and marine.

A Symbol of Hope

During intense winters, plants and trees go into a dormancy a period of stagnation. They withdraw the chlorophyll -a pigment responsible for green colour and a must for photosynthesis– from the leaves because they know that Sun is not going to come up strongly for photosynthesis to happen and food making process to start. The leaves change color to yellow, orange and mixture of these colors. Because besides chlorophyll which overpowers the colors of other pigments there are Xanthophylls which are yellow pigments, and carotenoids (the pigment which imparts the beautiful color to carrots, papaya, and mangoes and so on) which give leaves an orange color.

Slowly the leaves die and begin falling down. The tree branches become nude. But tree is not dead. It is waiting patiently for the tough time of winter to be over. As soon as the winter starts receding, the new leaves begin coming forth. The new beginning of life. At first, due to the absence of chlorophyll, the color of other pigments shine. Leaves are beautiful translucent. As the sun starts coming regularly with renewed force, chlorophyll starts building up masking the color of other pigments. Soon the leaves become intense green shade.

Thus the the new leaves are a symbol of Spring and new hope of brighter future. Let us hope and pray to God this also happens to the world….

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