|MadSci Network: Botany|
Flower colors of red, pink, blue and purple come mainly from the pigments called anthocyanins. Anthocyanins are water soluble pigments in the class of chemicals called flavanoids, which are phenolics. Anthocyanins are found in the cell vacuoles and are glucosides meaning they contain a sugar molecule. A classic experiment uses the anthocyanins in red cabbage as a pH indicator because anthocyanins change color depending on the pH. You could do the same thing with flower petals. An easy way is to crush a red rose petal on a white plate with the back of a spoon and add either vinegar (acid) or baking soda (base) and note the color change. A college lab manual has an experiment on chromatography of flower anthocyanins (Witham et al. 1971). Flowers may also contain another class of pigments called carotenoids, which are responsible for red in tomato and orange in carrot root. Carotenoids are red, yellow and orange in color. They do not reside in the vacuole but in organelles called plastids, either in green chloroplasts or in nongreen chromoplasts. References Red Cabbage pH Indicator Red/Purple Cabbage pH Indicator Genetics and Biochemistry of Anthocyanin Biosynthesis The Plant Cell Vol 7, 1071-1083, 1995. (PDF file). Witham, F.H. et al. 1971. Experiments in Plant Physiology. New York: Van Nostrand Reinhold.
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