|MadSci Network: Botany|
Plants have three major groups of pigments that color flowers and fruits, anthocyanins, carotenoids and betalains. Anthocyanins are found in vacuoles and change color as the pH changes. These are the pigments that you need for a color change to occur when using ammonia. Ammonia produces a high pH. Students often extract anthocyanins from red or purple cabbage and use them as a pH indicator. Carotenoids are present in plastids and are usually yellow, orange or red. Lycopene is the red carotenoid found in tomato fruit. Beta-carotene is the orange carotenoid found in orange carrot roots. Betalains replace anthocyanins in some plants, such as bougainvillea, cactus and red beet. Betalains and carotenoids do not change color with pH as anthocyanins do. The purple carnation (Dianthus caryophyllus) behaved as if it contained anthocyanins. The pink and red carnations behaved as if they lacked anthocyanins. You might have had white carnations that had been dyed pink or red with an artificial dye. Florists often dye white carnation flowers to produce other flower colors, especially the green carnations sold for St. Patrick's Day. If you can, crush some of the pink and red carnation petals before exposing them to ammonia vapor. Crushing would assure that the ammonia could enter the cell and reach the pigment. If a color change occurs when crushed petals are exposed to ammonia, it could confirm that anthocyanins were present. Some websites indicate that colored flowers exposed to ammonia turn green because the colored pigment is destroyed by the ammonia and the green chlorophyll is revealed. Chlorophyll does not have to be present because anthocyanins can change from purple or red to green as shown in the first two webpages in the references. References Red Cabbage pH Indicator Photos of anthocyanin solution at various pHs Introduction to the Caryophyllids - the Betalain Bunch Where does the color come from in purple cabbage? http://www.factsonfile.com/newfacts/Pdfs/44252/3-02.pdf
Try the links in the MadSci Library for more information on Botany.