The colors of the flowers are due to the pigment molecules that accumulate in their petals – and sometimes in other parts of the flower -. There are pigments of various types that, combined, give rise to a very wide range of colors. They are, for example, the carotenoids that are also responsible for the red color, orange or yellow of many fruits, or alkaloids such as betaine that gives blood red color to the root of the beet. But the most widespread floral pigments in the different species are the flavonoids, which normally produce blue and yellow pigments and sound a lot since the flavonoid family belongs to a good number of compounds with antioxidant capacity that are very fashionable because They are considered healthy.
These pigments that accumulate in the flowers absorb a part of the spectrum of light and reflect and transmit another. Therefore, the color you see is the one in the reflected and transmitted spectrum. The structure and morphology of the surface of the petal also contributes to this, which sometimes has cells that act as prisms and tint the colors associated with the pigments. It has only been shown that the colors of flowers serve one thing: to interact with pollinators, mainly insects and other arthropods, some birds and a few mammals. So the evolutionary explanation that flowers have colored petals is to attract their pollinators. The plant is a huge energy effort to manufacture and accumulate large amounts of pigments but it is worth it because its reproduction depends on it. Having colored flowers is not the only strategy to attract pollinators (think of orchids that look like insects, in the most varied aromas or sweet nectar) but it is one of the most important.
The predecessor plants of which we know today were once only green, and even now not all species have colored flowers, and in some the petals are practically indistinguishable from the leaves and have green color by chlorophyll. The plants that do not need pollinators usually have little showy flowers and no colors. The pigments are also produced in the rest of the plant and play a fundamental role in protecting against the environment, for example, filtering harmful UV rays or acting as antioxidants or deterrents for predators that feed on leaves, roots or fruits.
A very curious thing is that the color that we humans see in a flower it is not the same one that sees an insect because the eyes of insects are sensitive to different wavelengths. There are flowers that according to our vision have the petals of a homogeneous color, but if you look at them with filters that simulate the vision of an insect you see that they have much more exaggerated patterns. Sometimes they form patterns that direct the insect to the central part of the flower where the stamens and pistils are, which are the reproductive parts of the flower.
It is also interesting to know that there are some ornamental flowers, such as petunias, which have different colors, even on the same plant. And one wonders why this happens in the same species. These different colors in the different varieties that sometimes have spectacular coloration patterns with stripes or with the center of one color and the outside of another, are due to the so-called jumping genes or transposons. The transposons are infectious genetic elements that we have all the organisms in our genomes and that are jumping from one place to another, and falling into a gene that is responsible for the color of the flower, inactivate it. Depending on where and at what stage of the development of the flower the transposon jumps, the flower will have chromatic or other patterns. This is very interesting because, apart from providing us with some petunias beautiful for our garden, researchers have used it to study the genetics of plants. The transposons were discovered by the American researcher Barbara McClintock, who studied corn plants with different color grains on the same ear. Her discovery earned her the Nobel Prize in Medicine in 1983, becoming the first woman to receive this award and, until today, the only woman who has obtained it alone. As you see, the colors of the plants have given a great service to science, discovering important mechanisms of inheritance applicable to all living beings. In addition to brightening the view!
Carmen Fenoll is Professor of Plant Physiology at the University of Castilla La Mancha and President of the Spanish Society of Plant Physiology.
Question done via email by Carlos Martín
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