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Photosynthetic Pigments

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  • Difficulty Level : Medium
  • Last Updated : 17 Feb, 2023
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The process by which plants convert carbon dioxide, water, and sunlight into oxygen and energy in the form of sugar is known as photosynthesis. Autotrophic plants produce their own food through a process called photosynthesis. Sunlight, chlorophyll, CO2, and water are four crucial components needed for this process. The two steps of photosynthesis are the Light Reaction and the Dark Reaction.

  • Light reaction: The initial stage of photosynthesis is the light reaction, in which solar energy is transformed into chemical energy in the form of ATP and NADPH. Protein complexes and pigment molecules both contribute to the synthesis of NADPH and ATP.
  • Dark reaction: The dark reaction is also known as the carbon-fixing process. It is a light-independent mechanism that produces sugar molecules from carbon dioxide and water molecules. The dark reaction takes place in the stroma of the chloroplast, where the products of the light reaction are used.

Photosynthetic Pigments

Photosynthesis Pigments


Pigments are chemical compounds which reflect only certain wavelengths of visible light. They appear “colourful” as a result. Pigments are what give flowers, corals, and even animal skin their colours. The capacity of pigments to absorb particular wavelengths of light is more significant than their ability to reflect light.

Pigments are helpful to plants and other autotrophs—organisms that produce their own food through photosynthesis—because they interact with light to absorb only specific wavelengths. Pigments serve as the mechanism by which the energy of sunlight is absorbed for photosynthesis in plants, algae, and cyanobacteria. However, because each pigment reacts with only a small portion of the spectrum, it is typically necessary to make a variety of pigments, each with a distinct colour, in order to capture more of the spectrum.

Anthocyanins, betalains, carotenoids, porphyrins, and many more are other crucial plant pigments. By reflecting the wavelengths, all of these pigments promote the process of chemical reactions.

1. Chlorophyll



Chlorophyll pigments are greenish pigments with a porphyrin ring. This is a stable ring-shaped molecule with unfettered electron migration. Because electrons flow freely, the ring has the ability to easily gain or lose electrons and hence the ability to provide energised electrons to other molecules. This is the basic method through which chlorophyll “captures” solar energy.

There are various types of chlorophyll, the most essential of which is chlorophyll “a.” This is the molecule that enables photosynthesis by sending energised electrons to molecules that produce sugars. Chlorophyll “a” is found in all photosynthetic plants, algae, and cyanobacteria. The second type of chlorophyll is chlorophyll “b,” which is found only in “green algae” and plants. A third frequent form of chlorophyll is known as chlorophyll “c,” and it is present solely in photosynthetic members of the Chromista as well as dinoflagellates. One of the earliest indications that these primary groups were not as closely linked as previously thought was the variances in chlorophylls.

Synthesis of Chlorophyll

Chlorophyll is produced within the chloroplast from an abundant precursor, glutamate. The processes occur in the plastid stroma and are catalysed by soluble enzymes from glutamate to the tetrapyrrole protoporphyrin IX, where the route splits between chlorophyll and heme.

Functions of Chlorophyll

The chlorophyll pigment is responsible for plants’ green colouration. Chlorophyll is one of several pigments that are employed in photosynthesis to transform sunlight energy into chemical energy.

For more about Chlorophyll.

2. Carotenoids

Carotenoids are pigments that are often red, orange, or yellow in colour and contain the well-known compound carotene, which gives carrots their colour. These compounds are made up of two tiny six-carbon rings that are linked together by a “chain” of carbon atoms. As a result, they do not dissolve in water and must be connected to cell membranes. Carotenoids cannot directly transfer sunlight energy to the photosynthetic pathway, but must instead transport it through chlorophyll. As a result, they are known as accessory pigments. Fucoxanthin, a brown pigment that colours kelps and other brown algae as well as diatoms, is one of the most noticeable accessory pigments. 

Synthesis of Carotenoids

All photosynthetic organisms (including plants) and certain non-photosynthetic bacteria and fungi generate carotenoids. Plant carotenoids are tetraterpenes produced from phytoene, a 40-carbon isoprenoid.

Functions of Carotenoids

Carotenoids, like chlorophylls, are important pigments in photosynthetic organs. Carotenoids also operate as photo protectors, antioxidants, colour attractants, and plant hormone precursors in non-photosynthetic plant organs.

3. Phycobilins

Phycobilins are water-soluble pigments that can be found in the cytoplasm or the chloroplast stroma. They are only found in Cyanobacteria and Rhodophyta.

Phycobilins are not only beneficial to the organisms that employ them to absorb light energy; they are also important as research instruments. Phycocyanin and phycoerythrin both glow at a specific wavelength. When exposed to bright light, they absorb the energy and release it by releasing light with a very limited wavelength range. Because the light emitted by this fluorescence is so unique and consistent, phycobilins can be employed as chemical “tags.”

The colours are chemically linked to antibodies, which are subsequently placed in a cell solution. A machine can determine if the cells in the droplets have been “tagged” when the solution is sprayed in a stream of fine droplets past a lase. 

Synthesis of Phycobilins

The phycobilins are created through the reduction of biliverdin, which is produced during the production and breakdown of heme. This heme is a necessary step in the production of phycobilins.

Functions of Phycobilins

The fundamental function of phycobilins, like carotenoids, is to complement the light-capturing ability of Chl by absorbing energy where Chl is inefficient. Phycobilins absorb green to red wavelengths of light, whereas carotenoids absorb mostly in the blue-green area.

4. Anthocyanins

Anthocyanins are antioxidants found in fruits and vegetables that are red, purple, or blue. They are members of the flavonoid family, which includes the antioxidants found in wine, tea, and dark chocolate. Flavonoids are antioxidants that are part of a broader group known as polyphenols, which are thought to help prevent or treat health issues associated with inflammation and oxidative stress. Cancer, heart disease, and age-related mental illnesses are among these conditions.

Anthocyanin-containing foods have been utilised in traditional cures for decades. Studies are increasingly supporting its alleged health benefits. Plant-derived anthocyanins are also extensively utilised as dyes, natural food colourants, and culinary additives. For example, the commercial addition E163 is derived from grape skin and is often used to provide a purple colour to jam, candies, and beverages.

Synthesis of Anthocyanins

The anthocyanin biosynthetic pathway is a branch of the overall flavonoid pathway that begins with the chalcone synthase (CHS)-mediated synthesis of naringenin chalcone from 4-coumaroyl-CoA and malonyl-CoA.

Functions of Anthocyanins

Anthocyanins are a type of polyphenolic pigment found throughout the plant kingdom. Anthocyanins in plants not only aid in reproduction by attracting pollinators and seed dispersers, but they also defend against a variety of abiotic and biotic challenges.

5. Flavonoids

Flavonoids are plant metabolites that are hypothesised to have health advantages via cell signalling pathways and antioxidant properties. These compounds can be found in many fruits and vegetables.

Flavonoids are polyphenolic compounds with 15 carbon atoms that are water-soluble. They are made up of two benzene rings linked by a three-carbon chain. One of the carbons in this chain is linked to carbon in one of the benzine rings, either indirectly or directly, resulting in a third middle ring. Flavonoids are classified into six major subtypes: chalcones, flavones, isoflavonoids, flavanones, anthoxanthins, and anthocyanins. Many of these compounds, particularly anthoxanthins, contribute to the yellow hue of some petals, whereas anthocyanins are frequently present.

Synthesis of Flavonoids

Flavonoids are synthesised by the phenylpropanoid route, which converts phenylalanine into 4-coumaroyl-CoA, which then enters the flavonoid biosynthesis pathway. Chalcone synthase, the initial flavonoid pathway enzyme, generates chalcone scaffolds from which all flavonoids are derived.

Functions of Flavonoids

Flavonoids are structurally diverse secondary metabolites found in plants that serve a variety of functions. These range from plant development, pigmentation, and UV protection functions to a variety of roles in defence and signalling between plants and microorganisms.

FAQs on Photosynthesis Pigments

Question 1: What are the three types of photosynthetic pigments?


The three types of photosynthetic pigments are chlorophyll, carotenoids and phycobilin. 

Question 2: What is the main photosynthetic pigment? 


The main photosynthetic pigment is chlorophyll-a.

Question 3: Which pigment is present in a leaf of higher plants?


The pigments found in the leaf are chlorophyll-a, chlorophyll-b, carotenoids, and xanthophylls.

Question 4: What colour are different pigments on a chromatogram? 


Chlorophyll-a appears bright or blue-green in paper chromatography/chromatogram, chlorophyll-b as yellow-green/grass green, xanthophylls as yellow, and carotenoids as yellow to yellowish orange.

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