Plant Pigments | Agriculture Optional Notes for UPSC PDF Download

What is a pigment?

In the field of biology, a pigment refers to any colored substance present within the cells of plants or animals. Pigments are responsible for imparting color to various aspects of living organisms, including skin, hair, eyes, and plant tissues. They determine the visible hues in objects by absorbing specific wavelengths of light and reflecting others. In plants, three primary pigments are prominent: chlorophylls, carotenoids, and flavonoids.

Types of Pigments

Chlorophylls

• Chlorophylls are responsible for the green coloration in plants and are crucial for the process of photosynthesis.
• They absorb light energy, which is used by plants to convert carbon dioxide and water into carbohydrates and oxygen.
• Chlorophyll is primarily produced in cellular organelles called chloroplasts.
• There are two main types of chlorophyll in green plants, chlorophyll a and chlorophyll b, with similar structures but differing in one side chain.
• Chlorophyll a and b absorb light in the blue and red regions of the electromagnetic spectrum, but they have distinct peaks in different parts of the spectrum.
• Chlorophylls do not absorb much light in the green part of the spectrum (490 to 550 nanometers) and instead reflect green light, making plants with these pigments appear green.
• Chlorophyll a produces dark green colors, while chlorophyll b yields yellowish green hues.
• Chlorophyll a is more abundant in plants, constituting about three-quarters of the pigments.
• Chlorophyll b, often termed an accessory pigment, widens the range of visible light absorption, which can be beneficial for plants in low-light conditions.

Carotenoids

• Carotenoids are responsible for the yellow, orange, and red colors found in various fruits, vegetables, and flowers.
• One common carotenoid, beta-carotene, is present in the chromoplasts of sunflower petals, creating vibrant yellow and orange hues.
• Beta-carotene is also the pigment responsible for the orange coloration in carrots and sweet potatoes.
• During the autumn season, carotenoids become visible in leaves when chlorophyll breaks down due to reduced sunlight exposure.
• Carotenoids absorb light in the blue and green regions of the spectrum (wavelengths from 400 to 600 nm) and reflect light in the yellow, orange, and red parts of the spectrum.
• There are two primary types of carotenoids: carotenes and xanthophylls.
• Carotenes include pigments like beta-carotene and lycopene, with a chemical formula of C40H56, and their names typically end in -ene.
• Xanthophylls include pigments like lutein and zeaxanthin, which have a structure similar to carotenes but contain additional oxygen molecules, and their names end in -in.
• Xanthophylls are present in many green vegetables and some flowers and are sometimes used as food colorants.
• Carotenoids absorb sunlight and transfer the energy to chlorophyll molecules, aiding photosynthesis.
• Additionally, carotenoids act as antioxidants in living organisms, helping to mitigate cell-damaging oxidation reactions.

Flavonoids

• Flavonoids are a group of compounds found in plants and produce red, yellow, blue, and purple colors.
• The most common type of flavonoid is anthocyanin, which is located in cell vacuoles.
• The red coloration observed in roses, apples, cherries, red cabbage, and autumn maple leaves is due to anthocyanins.
• Many flavonoid pigments absorb light in wavelengths ranging from 250 to 550 nm, with the highest absorption occurring in the ultraviolet and blue-green parts of the spectrum.
• Flavonoids reflect light in the blue and violet regions of the spectrum, resulting in a purplish appearance.
• Flavonoids have many different functions.
• For example, they are responsible for some of the colour and aroma in flowers and fruit. Because they reflect light in the ultraviolet part of the spectrum, insects who see in this range can spot them easily. This can mean flowers with flavonoids are more visible to pollinatorspollinators.
• Flavonoids also help protect plants from stresses like ultraviolet light, frost, heat, and dry conditions.
• Scientists have studied flavonoids because of their potential health benefits to humans. These compounds have anti-inflammatory properties, and they may help prevent cancer.