After our lab on Tuesday where we used red-cabbage paper as indicator of pH, I was interested in learning more about anthocyanins, or the chemical that makes the paper turn blue or pink in the presence of bases or acids.
Anthocyanins are water-soluble pigments that belong to a class of molecules called flavonoids. They are present in many common plants including blueberries, cranberries, eggplants, and black rice. They often give off a purplish hue.
In flowers, bright reds and purples are adaptive for attracting pollinators. In fruits, the colorful skins also attract the attention of animals, which may eat the fruits and disperse the seeds. In photosynthetic tissues, such as leaves and stems, anthocyanins have been shown to act as a “sunscreen” protecting cells from high-light damage by absorbing blue-green and ultraviolet light, thereby protecting the tissues from high-light stress. This has been shown to occur in autumn leaves and broad-leaf evergreen leaves that turn red during the winter. The red coloration of leaves has been proposed to possibly camouflage leaves from herbivores blind to red wavelengths, or signal unpalatability, since anthocyanin synthesis often coincides with synthesis of unpalatable phenolic compounds.
Additionally, studies indicate that anthocyanins may also serve as powerful antioxidants.
I found it surprising that anthocyanins had so many alternative functions besides just simply acting as an indicator of pH. Not only are the purplish hues pretty to look at, they are highly functioning too!
It’s especially interesting that they act as a sort of sunscreen for plants – we normally don’t think of plants and animals needing sunscreen, but I guess too much UV light isn’t good for any organism. I hadn’t thought about the wavelengths of light that these compounds might absorb outside of the pretty colors in the visible spectrum, but it’s good to be reminded that invisible wavelengths are quite important as well!