PIGMENTS: door to our colorful world.

Aren’t we fascinated by the colorful world around us so what is it that makes our world so colorful and vibrant? The answer lies in the presence of “pigments,”, a coloring matter found in the cells of both plants and animals. These pigments are responsible for the diverse colors we see around us. The biological pigments produced by living organisms absorb certain wavelengths of light and reflect others. We are all familiar with the green pigment chlorophyll that plants possess to trap light energy to carry out photosynthesis. Besides photosynthesis, plant pigments also help to attract insects for pollination, ultimately helping in fruit formation. But why do animals produce pigments? Animals have dark pigments like melanin (in skin, eyes, and fur) and its main purpose is to prevent damage caused to the tissues by the UV (ultra-violet) light.

MAJOR PIGMENTS IN PLANTS

The principal pigments in plants are Chlorophyll, Carotenoids, Flavonoids, and Betalains.

Chlorophyll is one of the major pigments found in plants that imparts a green color to the foliage and leaves. Besides plants, cyanobacteria (blue-green algae) and algae possess chlorophyll. Chlorophyll mainly absorbs red light (long wavelength) and blue light (short wavelength) of the visible spectrum and reflects the green spectrum. Chlorophyll is of five main types Chlorophylls a, b, c, d and related molecule bacteriochlorophyll found in prokaryotes.

Carotenoids (carotenes and xanthophylls) are the plant pigments responsible for bright red, yellow and orange colors of fruits and vegetables (e.g., pumpkins, carrots, corn, tomatoes). It is produced not only by plants and algae and by bacteria and fungi. Carotenoids absorb light in the blue-green and violet region and reflect orange, red, and yellow wavelengths of light. Carotenoids perform an important function in photosynthesis and photoprotection. Carotenoids are beneficial antioxidants that protect us from various diseases. Provitamin A carotenoids can be converted into vitamin A and are important for eye health.

Flavonoids, its common types include anthocyanins, aurones, flavonols, and proanthocyanidins. Flavonoids are abundant in the plants and most important for flower coloration. They produce yellow or red/blue pigmentation in petals aiding in attracting insects for pollination. In higher plants, flavonoids filter UV light and are also involved in symbiotic nitrogen fixation and pigmentation in flowers. Flavonoids also play an important role in plant defense. Flavonoids are synthesized only in the plants and they exhibit antioxidant activity.

Betalains, its common type includes betacyanins, and betaxanthins are a group of reddish pigments. In the plant kingdom, we find these in the leaves, roots, stalks, flowers, fruits, seeds and grains. Red beetroot, amaranth, prickly pear, and red pitahaya contain betalains. Betalains also contain antioxidant properties.

PIGMENTS IN AMINALS

The main pigment found in most of the mammals is the melanin, present in special cells called chromatophores and is responsible for eyes, skin, hair and fur color. Melanin protects the skin from harmful ultraviolet rays. The integuments of birds contain two different forms of melanin: Eumelanin (responsible for black, brown or grey coloration) and Pheomelanin (produces lighter yellowish to reddish coloration). However, most pigments are not made in the body, animals consume different things in their diet that impart them a certain color, for example, flamingoes are not pink. They are born grey but their diet comprises blue-green algae and brine shrimp, which turn them pink because of natural pink dye called canthaxanthin. Similarly, blue-footed boobies have bright blue feet to attract mates. Their blue color feet results from carotenoid pigments of their fishy diet.

Blue pigment is the rarest pigment in nature, and it is considered tough for a bird's body to create through dietary pigments. Blue color birds result from an illusion, such birds have special structures in their feathers that break up the light and reflect only blue. This is considered true for blue and green birds (parrot). Parrots lack any green pigment but appear green because of light scattering (Tyndall effect).  Likewise, blue butterflies appear blue because of the microscopic structure of the scales and because of the interference of light. The only butterfly that produces a blue pigment is an “olive wing” butterfly. Many green snakes and frogs are not green but possess a yellow pigment and blue structural color and these two combined produce green effect.

There are various animals that protect themselves from their predators through their biological pigments i.e., they use their biological pigments to camouflage (e.g., chameleons), for warning coloration and for mimicry.