Plants are solar-powered. They produce their own food by harvesting energy from light via the chemical miracle photosynthesis. Photosynthesis is represented by the following chemical formula:
6H20 + 6CO2 + light photons = C6H12O6 + 6O2
In other words, plants turn water, carbon dioxide and light into glucose (sugar) and oxygen. Photosynthesis occurs in plant pigments—chemical compounds that selectively absorb particular wavelengths of light. The light not absorbed by the pigments is reflected and these colors are what appear to the observer’s eye. This color can be used by plants to attract pollinators, such as birds or insects, or to attract or deter predators, depending on the circumstance. Here is a breakdown of the four classes of plant pigments.
Chlorophyll is the most important plant pigment. A chlorophyll molecule harvests certain wavelengths of light required to power photosynthesis, and the leftover radiation (mainly green light) is reflected off of the plant’s leaves. Some scientists argue that chlorophyll is the most important organic molecule on Earth. It is found in algae, plants and certain types of photosynthetic bacteria.
There are six types of chlorophyll molecules that differ slightly in arrangements of atoms and bonds, known simply as chlorophyll A (the most common), chlorophyll B, chlorophyll C1, chlorophyll C2, chlorophyll D and chlorophyll F. Chlorophyll molecules are found in the chloroplasts of plant cells. They feature a magnesium ion at the center of the molecule and plenty of nitrogen, which is why availability of these elements in a soil or fertilizer regimen is important. There is one type of sea slug that has been found to photosynthesize using chlorophyll to produce its own food. The slug eats photosynthetic algae and somehow keeps the chloroplasts functioning to harvest light. I would save so much money on dog food if he could just photosynthesize.
Carotenoids are a class of pigments responsible for many of the reds, yellows and oranges in the plant and animal kingdoms. They are produced in plants and some bacteria and fungi. Animals cannot manufacture them so they must obtain them from their diet. Egg yolks, butter, carrots and cantaloupe get their color from carotenoids. Carotenoids are synthesized in plants from aromatic terpenes and terpenoids. There are two subcategories of carotenoids: xanthophylls and carotenes. Xanthophylls contain oxygen, while carotenes do not. Some common carotenoids are lycopene, lutein and beta-carotene.
Carotenoids have a variety of functions in plants. Some play a role in photoprotection and help buffer light harvesting in photosynthesis. They absorb light in blue frequencies and protect plants from harmful UV radiation. As antioxidants, they seek out destructive free radicals and eliminate them. When ingested by humans, some carotenoids are converted to retinal (vitamin A).
People that regularly eat diets rich in carotenoids display improved cognitive skills, enhanced immune systems, less bone loss and enriched overall health. There is one species in the animal kingdom that has evolved to synthesize its own carotenoids. The red pea aphid is able to photosynthesize using carotenoids. They have stolen these genes from a bacteria or fungi, a process called lateral gene transfer. Lions and tigers and photosynthetic, gene-stealing pea aphids, oh my!
Anthocyanins are the plant pigments behind a number of the beautiful reds, purples and blues in plants. They give berries, red wine and African violets their color and are found in the vacuoles of plant cells. Anthocyanins are the main pigments responsible for autumn foliage. Plants produce them in late summer, when chlorophyll is being deactivated.
Anthocyanins are extremely pH-dependent. Hydrangea flowers will be pink in acid soil and blue in alkaline soil due to the pH-sensitivity of these pigments. Anthocyanins are often used to attract specific pollinators. They can be used by plants to either attract predators to spread seeds, or deter herbivore predators that are attracted to green colors. In leaves, they act as a sunscreen by absorbing harmful radiation not absorbed by chlorophyll.
Anthocyanins display analgesic, as well as anti-inflammatory, characteristics. Some anthocyanins have also shown some promise in anti-anxiety and anti-cancer applications. The future of anthocyanins is bright (no pun intended). Their ability to harvest light energy and convert it to usable electrical energy means they might one day be used in solar cells.
Betalains are the least common of the four classes of plant pigments. They are red and yellow pigments that sometimes replace anthocyanins.
Plants either have one or the other. They are responsible for the deep red color of beets, which they are named after. They are also found in red bougainvillea and also in the bright flesh of some unique cacti. Hopi Indians used an extract of amaranth flowers containing betalains as a bright red dye. Like anthocyanins, they are found in the vacuole of plant cells. They are antioxidants and their color is pH-sensitive.
There are two types of betalains: betacyanins (red-purple) and betaxanthins (yellow-orange). Both types possess natural fungicidal properties and are synthesized from tyrosine, an essential amino acid. Like chlorophyll, betalains contain nitrogen and are reliant on nitrogen sources in the soil or nutrient program.