Originally, vitamin A is an invention of the plant. Over the long history of their development, they have always been attacked by aggressive substances such as free radicals, parasites, bacteria, viruses, etc. Against these aggressions, plants have developed defense mechanisms, improved from one generation to another. So,people are not the perfect "producers" of the immune system, but plants are.
Million years, plants extract from their environment carbon of atoms to produce, with their help, carotene, a pigment that stains plants so beautiful . Moreover, beautiful shades of red or pink of salmon and lobster or red plumage of the bird flamingo are nothing but a strong accumulation of molecules of carotene. But nature is not vain, she is not interested in being beautiful, carotene accomplishes far more important functions: protect plant cells from hostile microorganisms.
When dawn is coming, free radicals smell their chance: these aggressive-destructive substances, can be characterized as "sent" by the sun. When herbs, ferns, flowers and trees tumble their oxygen, in every cell in part is produced a chaos in which free radicals are trying to take advantage,burning unprotected cells by oxidation.
But carotene prevents them to do. Without carotene,in the morning, at 9, gorgeous flora of Central Europe should be burned, turned into a wilted material. Inventing carotene, nature has created a perfect weapon for protection against free radicals. And because there were appeared new and new types of free radicals, plants armored their cells - gradually - with over 500 different types of carotene.
Carotenoids,with no exceptions,are known to present in close association of chlorophylls in all photosynthesizing cells. Most of the carotenoids are yellow or orange in colour, found as chromoprotein in thylakoids. In general there are two major groups of carotenoids: the carotenes and the carotenols. Both of them are soluble in organic solvents. The carotenes are unsaturated hydrocarbons, absorb blue and green lights and transmit yellow and red light. The greatest function of these carotenoids is to protect chlorophyll molecules from photo-oxidation.These pigments are also known to absorb light and transfer energy.