Pigments in Plants definition : Substances can absorb light of a specific wavelength and produce color.
Importance:
Pigments in plants cell’ chloroplasts absorb the light and energize electrons, raising them to a higher energy level. It is the energy used to produce ATP and reduce NADP to NADPH.
The release of energy from ATP and the oxidation of NADPH are then used to incorporate CO2 into organic molecules.
Types:
There are the following pigments that help out in the process of photosynthesis and color production:
- Chlorophyll
- Carotenoids
- Phycobilins
Chlorophyll:
Chlorophyll is any of several related green pigments found in cyanobacteria and the chloroplasts of algae and plants. Its name is derived from the Greek words chloros (“green”) and phyllon (“leaf”).
Physical properties:
- It is the primary pigment in plants. Chlorine absorbs yellow and blue wavelengths of light while reflecting green.
- Chlorophyll is found in the thylakoid sacs of the chloroplast. The chloroplast is a specialized part of the cell that functions as an organelle.
- Photosynthesis can begin once the chlorophyll absorbs the appropriate wavelengths of light into the thylakoid sacs.
- They are fat soluble.
Classification and distribution of Chlorophyll:
- Chl a found in all green plants, including algae.
- Chl b is found in higher plants and some algae, e.gchlorophyceae, Euglenophyceae, and Charophyceae.
- Chl c found in lower vascular plants e.g bryophytes and in bacillariophyta,phaephyta.
- Chl d found in red algae.
- Chl e is rarely found in some golden algae.
Molecular Nature:
There are several types of chlorophyll, but all shares the chlorin magnesium ligand, which forms the right side of the diagram. The molecule consists of a 4_porphyrin ring as the head and phytol as the tail.
This is a stable ring-shaped molecule around which electrons are free to migrate. Because the electrons move freely, the ring can gain or lose electrons easily and, thus, provide energized electrons to other molecules. This is the fundamental process by which chlorophyll “captures” the energy of sunlight.
Chemical Nature:
Chemically chlorophyll consists of C, H, and O, with Mg as the central atom.
Chlorophyll a: C55H72O5N4Mg (CH3), Special group is methyl.
Chlorophyll b: C55H70O6N4Mg (CHO), a special group, is an aldehyde
Chlorophyll c1 + c2: C35H30O5N4Mg , C35H28O5N4Mg
Chlorophyll d: C54H70O6N4Mg
Biosynthesis of chlorophyll:
Succinyl-CoA and glycine react to form an intermediate product δ-Aminolevulinic acid 2 molecules of δ-Aminolevulinic acid react with each other to give porphobilinogen 4 molecules of porphobilinogen fuse to give protochlorophyll.
Then protochlorophyll reacts with 2H to synthesize chlorophyll in the presence of sunlight.
Succinyle coA + glycine –———————––> δ -Aminolivolinic acid
2 molecules of δ -Aminolevulinic acid ––—————-–>Porphobilinogen
4 molecules of porphobilinogen ––—————-–>protochlorophyll
Protochlorophyll + 2 H ———––(Sunlight)––—->Chlorophyll
Carotenoids:
Carotenoids are fat-soluble pigments and open chain conjugate molecules found throughout nature
Occurrence:
They are found principally in plants, algae, and photosynthetic bacteria, which play a critical role in the photosynthetic process. They also occur in some non-photosynthetic bacteria, yeasts, and molds, where they may protect against damage by light and oxygen.
Carotenoids are responsible for many of the red, orange, and yellow hues of plant leaves, fruits, and flowers and the colors of some birds, insects, fish, and crustaceans.
Classification:
Carotenoids are classified according to their structure as follows:
- The hydrocarbon carotenoids are known as carotenes example, alpha-carotene, Βeta-carotene, etc.
- Generala formula: C40H56
- Show photosystem 1
- Color: OrangeColor
2. The oxygenated carotenoids, derivatives of these hydrocarbons known as xanthophylls, are examples of these compounds zeaxanthin and lutein, etc.
- Show photosystem 2
- formula: C40H56O2
- Color: Yellow
Function:
Carotenoids are essential for plant life, providing essential photoprotective functions during photosynthesis, light harvesting, and prevention of photo-oxidative damage, and serving as precursors for the biosynthesis of the phytohormone abscisic acid (ABA). They have a role in the attraction of pollinators.
Phycobilins:
A group of red or blue photosynthetic water-soluble pigments. They are open-chain tetrapyrroles. The phycobilins are especially efficient at absorbing red, orange, yellow, and green light, wavelengths not well absorbed by chlorophyll a.
Organisms growing in shallow waters tend to contain phycobilins that can capture yellow/red light. In contrast, those at greater depth often contain more phycobilins that can capture green light, which is relatively more abundant there. There are three types of phycobilins:
- Phycoerythrin: Phycoerythrin absorbs green, yellow, and blue light and transmits red light. It is found in red algae.
- Phycocyanin: Phycocyanin is a pigment-protein complex from the light-harvesting phycobiliprotein family. Phycocyanins are found in Cyanobacteria.
- Allophycocyanin: Allophycocyanin (APC) is an intensely bright phycobiliprotein isolated from red algae that exhibit far-red fluorescence with high quantum yields. It is excited by laser lines at 594 and 633 nm, with an absorbance maximum of 650 nm and a fluorescence emission peak at 660 nm.
Location of phycobilins:
They are found outside the thylakoid membrane in small bodies called phycobilisomes.
Key Points – Pigments in plants
- 🌿 Chlorophyll is the primary pigment in plants and is responsible for absorbing yellow and blue wavelengths of light while reflecting green.
- 🌽 Pigments in plants, including chlorophyll, carotenoids, and phycobilins, play a crucial role in photosynthesis and color production.
- 🌞 Light absorbed by pigments in chloroplasts energizes electrons, which are used to produce ATP, reduce NADP to NADPH, and incorporate CO2 into organic molecules.
- 🎨 Carotenoids are fat-soluble pigments in plants, algae, and photosynthetic bacteria. They contribute to the leaves, fruits, and flowers’ red, orange, and yellow hues.
- 🌊 Phycobilins are water-soluble pigments found in some algae. They efficiently absorb red, orange, yellow, and green light, complementing the absorption spectrum of chlorophyll.
- 🧪 Chlorophyll molecules consist of a porphyrin ring and a phytol tail, enabling them to capture and transfer energy from sunlight.
- 📚 Chlorophyll is classified into different types (a, b, c, d, and e) based on their molecular structure and distribution in various organisms.
- 🔬 Carotenoids are divided into carotenes (hydrocarbon carotenoids) and xanthophylls (oxygenated carotenoids). They have photoprotective functions and serve as precursors for abscisic acid biosynthesis.
- 🔴 Phycobilins are red or blue water-soluble pigments found in algae. They efficiently absorb light in the green, yellow, and red range, complementing chlorophyll’s absorption spectrum.
- 📊 Phycobilins are located in phycobilisomes, small bodies outside the thylakoid membrane. They vary in composition based on the light conditions in which organisms grow.